Merge pull request #3021 from mthom/rebis-dev

Merge rebis-dev to master

.github/workflows/ci.yml

@@ -2,7 +2,9 @@ name: CI
 
 on:
   push:
-    branches: [master]
+    branches: 
+      - master
+      - rebis-dev
     tags:
       - "v**"
   pull_request:
@@ -47,8 +49,7 @@ jobs:
           # FIXME(issue #2138): run wasm tests, failing to run since https://github.com/mthom/scryer-prolog/pull/2137 removed wasm-pack
           - { os: ubuntu-22.04,   rust-version: nightly, target: 'wasm32-unknown-unknown',   publish: true, args: '--no-default-features' , test-args: '--no-run --no-default-features', use_swap: true }
           # Cargo.toml rust-version
-          - { os: ubuntu-22.04,   rust-version: "1.85",  target: 'x86_64-unknown-linux-gnu'}
+          - { os: ubuntu-22.04,   rust-version: "1.87",  target: 'x86_64-unknown-linux-gnu'}
-          # rust versions
           - { os: ubuntu-22.04,   rust-version: beta,    target: 'x86_64-unknown-linux-gnu'}
           - { os: ubuntu-22.04,   rust-version: nightly, target: 'x86_64-unknown-linux-gnu', miri: true, components: "miri"} 
     defaults:

Cargo.lock

@@ -1673,9 +1673,9 @@ checksum = "241eaef5fd12c88705a01fc1066c48c4b36e0dd4377dcdc7ec3942cea7a69956"
 
 [[package]]
 name = "lock_api"
-version = "0.4.12"
+version = "0.4.13"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "07af8b9cdd281b7915f413fa73f29ebd5d55d0d3f0155584dade1ff18cea1b17"
+checksum = "96936507f153605bddfcda068dd804796c84324ed2510809e5b2a624c81da765"
 dependencies = [
  "autocfg",
  "scopeguard",
@@ -2011,9 +2011,9 @@ dependencies = [
 
 [[package]]
 name = "parking_lot"
-version = "0.12.3"
+version = "0.12.4"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "f1bf18183cf54e8d6059647fc3063646a1801cf30896933ec2311622cc4b9a27"
+checksum = "70d58bf43669b5795d1576d0641cfb6fbb2057bf629506267a92807158584a13"
 dependencies = [
  "lock_api",
  "parking_lot_core",
@@ -2021,9 +2021,9 @@ dependencies = [
 
 [[package]]
 name = "parking_lot_core"
-version = "0.9.10"
+version = "0.9.11"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "1e401f977ab385c9e4e3ab30627d6f26d00e2c73eef317493c4ec6d468726cf8"
+checksum = "bc838d2a56b5b1a6c25f55575dfc605fabb63bb2365f6c2353ef9159aa69e4a5"
 dependencies = [
  "cfg-if",
  "libc",
@@ -2712,6 +2712,7 @@ dependencies = [
  "num-order",
  "ordered-float",
  "ouroboros",
+ "parking_lot",
  "phf",
  "pprof",
  "proc-macro2",

Cargo.toml

@@ -11,7 +11,7 @@ keywords = ["prolog", "prolog-interpreter", "prolog-system"]
 categories = ["command-line-utilities"]
 build = "build/main.rs"
 # Remember to check CI
-rust-version = "1.85"
+rust-version = "1.87"
 
 [lib]
 crate-type = ["cdylib", "rlib"]
@@ -79,6 +79,7 @@ ego-tree = "0.10.0"
 
 serde_json = "1.0.122"
 serde = "1.0.204"
+parking_lot = "0.12.4"
 
 [target.'cfg(not(target_arch = "wasm32"))'.dependencies]
 crossterm = { version = "0.28.1", optional = true }
@@ -136,6 +137,7 @@ opt-level = 3
 [profile.release]
 lto = true
 opt-level = 3
+debug = 2
 
 [profile.wasm-dev]
 inherits = "dev"

README.md

@@ -72,7 +72,7 @@ Extend Scryer Prolog to include the following, among other features:
         (`atom`, `var`, etc) with if/else ladders. (_in progress_)
   - [ ] Inlining all built-ins and system call instructions.
   - [x] Greatly reducing the number of instructions used to compile disjunctives.
-  - [ ] Storing short atoms to heap cells without writing them to the atom table.
+  - [x] Storing short atoms to heap cells without writing them to the atom table.
 - [ ] A compacting garbage collector satisfying the five properties of
       "[Precise Garbage Collection in Prolog](https://www.complang.tuwien.ac.at/ulrich/papers/PDF/2008-ciclops.pdf)." (_in progress_)
 - [ ] Mode declarations.

build/instructions_template.rs

@@ -19,6 +19,7 @@ use to_syn_value_derive::ToDeriveInput;
  */
 
 use std::any::*;
+use std::rc::Rc;
 use std::str::FromStr;
 
 struct ArithmeticTerm;
@@ -28,6 +29,7 @@ struct Death;
 struct HeapCellValue;
 struct IndexingLine;
 struct Level;
+// struct Literal;
 struct NextOrFail;
 struct RegType;
 
@@ -535,6 +537,16 @@ enum SystemClauseType {
     UnsetEnv,
     #[strum_discriminants(strum(props(Arity = "2", Name = "$shell")))]
     Shell,
+    #[strum_discriminants(strum(props(Arity = "8", Name = "$process_create")))]
+    ProcessCreate,
+    #[strum_discriminants(strum(props(Arity = "2", Name = "$process_id")))]
+    ProcessId,
+    #[strum_discriminants(strum(props(Arity = "3", Name = "$process_wait")))]
+    ProcessWait,
+    #[strum_discriminants(strum(props(Arity = "1", Name = "$process_kill")))]
+    ProcessKill,
+    #[strum_discriminants(strum(props(Arity = "1", Name = "$process_release")))]
+    ProcessRelease,
     #[strum_discriminants(strum(props(Arity = "1", Name = "$pid")))]
     Pid,
     #[strum_discriminants(strum(props(Arity = "4", Name = "$chars_base64")))]
@@ -622,7 +634,7 @@ enum InstructionTemplate {
     #[strum_discriminants(strum(props(Arity = "2", Name = "get_list")))]
     GetList(Level, RegType),
     #[strum_discriminants(strum(props(Arity = "4", Name = "get_partial_string")))]
-    GetPartialString(Level, Atom, RegType, bool),
+    GetPartialString(Level, Rc<String>, RegType),
     #[strum_discriminants(strum(props(Arity = "3", Name = "get_structure")))]
     GetStructure(Level, Atom, usize, RegType),
     #[strum_discriminants(strum(props(Arity = "2", Name = "get_variable")))]
@@ -645,7 +657,7 @@ enum InstructionTemplate {
     #[strum_discriminants(strum(props(Arity = "2", Name = "put_list")))]
     PutList(Level, RegType),
     #[strum_discriminants(strum(props(Arity = "4", Name = "put_partial_string")))]
-    PutPartialString(Level, Atom, RegType, bool),
+    PutPartialString(Level, Rc<String>, RegType),
     #[strum_discriminants(strum(props(Arity = "3", Name = "put_structure")))]
     PutStructure(Atom, usize, RegType),
     #[strum_discriminants(strum(props(Arity = "2", Name = "put_unsafe_value")))]
@@ -875,6 +887,7 @@ fn generate_instruction_preface() -> TokenStream {
         use crate::arithmetic::*;
         use crate::atom_table::*;
         use crate::forms::*;
+        use crate::functor_macro::*;
         use crate::machine::heap::*;
         use crate::machine::machine_errors::MachineStub;
         use crate::machine::machine_indices::CodeIndex;
@@ -885,6 +898,7 @@ fn generate_instruction_preface() -> TokenStream {
         use indexmap::IndexMap;
 
         use std::collections::VecDeque;
+        use std::rc::Rc;
 
         fn reg_type_into_functor(r: RegType) -> MachineStub {
             match r {
@@ -896,9 +910,9 @@ fn generate_instruction_preface() -> TokenStream {
         impl Level {
             fn into_functor(self) -> MachineStub {
                 match self {
-                    Level::Root => functor!(atom!("level"), [atom(atom!("root"))]),
+                    Level::Root => functor!(atom!("level"), [atom_as_cell((atom!("root")))]),
-                    Level::Shallow => functor!(atom!("level"), [atom(atom!("shallow"))]),
+                    Level::Shallow => functor!(atom!("level"), [atom_as_cell((atom!("shallow")))]),
-                    Level::Deep => functor!(atom!("level"), [atom(atom!("deep"))]),
+                    Level::Deep => functor!(atom!("level"), [atom_as_cell((atom!("deep")))]),
                 }
             }
         }
@@ -911,7 +925,7 @@ fn generate_instruction_preface() -> TokenStream {
                         functor!(atom!("intermediate"), [fixnum(i)])
                     }
                     ArithmeticTerm::Number(n) => {
-                        vec![HeapCellValue::from((n, arena))]
+                        functor!(atom!("number"), [number(n, arena)])
                     }
                 }
             }
@@ -996,7 +1010,7 @@ fn generate_instruction_preface() -> TokenStream {
                 IndexingCodePtr,
                 IndexingCodePtr,
             ),
-            SwitchOnConstant(IndexMap<Literal, IndexingCodePtr, FxBuildHasher>),
+            SwitchOnConstant(IndexMap<HeapCellValue, IndexingCodePtr, FxBuildHasher>),
             SwitchOnStructure(IndexMap<(Atom, usize), IndexingCodePtr, FxBuildHasher>),
         }
 
@@ -1016,7 +1030,7 @@ fn generate_instruction_preface() -> TokenStream {
                     IndexingCodePtr::External(o) => functor!(atom!("external"), [fixnum(o)]),
                     IndexingCodePtr::Internal(o) => functor!(atom!("internal"), [fixnum(o)]),
                     IndexingCodePtr::Fail => {
-                        vec![atom_as_cell!(atom!("fail"))]
+                        functor!(atom!("fail"))
                     },
                 }
             }
@@ -1030,80 +1044,43 @@ fn generate_instruction_preface() -> TokenStream {
         }
 
         impl IndexingInstruction {
-            pub fn to_functor(&self, mut h: usize) -> MachineStub {
+            pub fn to_functor(&self) -> MachineStub {
                 match self {
                     &IndexingInstruction::SwitchOnTerm(arg, vars, constants, lists, structures) => {
                         functor!(
                             atom!("switch_on_term"),
                             [
                                 fixnum(arg),
-                                indexing_code_ptr(h, vars),
+                                indexing_code_ptr(vars),
-                                indexing_code_ptr(h, constants),
+                                indexing_code_ptr(constants),
-                                indexing_code_ptr(h, lists),
+                                indexing_code_ptr(lists),
-                                indexing_code_ptr(h, structures)
+                                indexing_code_ptr(structures)
                             ]
                         )
                     }
                     IndexingInstruction::SwitchOnConstant(constants) => {
-                        let mut key_value_list_stub = vec![];
+                        variadic_functor(
-                        let orig_h = h;
+                            atom!("switch_on_constants"),
-
+                            1,
-                        h += 2; // skip the 2-cell "switch_on_constant" functor.
+                            constants.iter().map(|(c, ptr)| {
-
+                                functor!(
-                        for (c, ptr) in constants.iter() {
+                                    atom!(":"),
-                            let key_value_pair = functor!(
+                                    [cell((*c)), indexing_code_ptr((*ptr))]
-                                atom!(":"),
+                                )
-                                [literal(*c), indexing_code_ptr(h + 3, *ptr)]
+                            }),
-                            );
-
-                            key_value_list_stub.push(list_loc_as_cell!(h + 1));
-                            key_value_list_stub.push(str_loc_as_cell!(h + 3));
-                            key_value_list_stub.push(heap_loc_as_cell!(h + 3 + key_value_pair.len()));
-
-                            h += key_value_pair.len() + 3;
-                            key_value_list_stub.extend(key_value_pair.into_iter());
-                        }
-
-                        key_value_list_stub.push(empty_list_as_cell!());
-
-                        functor!(
-                            atom!("switch_on_constant"),
-                            [str(orig_h, 0)],
-                            [key_value_list_stub]
                         )
                     }
                     IndexingInstruction::SwitchOnStructure(structures) => {
-                        let mut key_value_list_stub = vec![];
+                        variadic_functor(
-                        let orig_h = h;
-
-                        h += 2; // skip the 2-cell "switch_on_constant" functor.
-
-                        for ((name, arity), ptr) in structures.iter() {
-                            let predicate_indicator_stub = functor!(
-                                atom!("/"),
-                                [atom(name), fixnum(*arity)]
-                            );
-
-                            let key_value_pair = functor!(
-                                atom!(":"),
-                                [str(h + 3, 0), indexing_code_ptr(h + 3, *ptr)],
-                                [predicate_indicator_stub]
-                            );
-
-                            key_value_list_stub.push(list_loc_as_cell!(h + 1));
-                            key_value_list_stub.push(str_loc_as_cell!(h + 3));
-                            key_value_list_stub.push(heap_loc_as_cell!(h + 3 + key_value_pair.len()));
-
-                            h += key_value_pair.len() + 3;
-                            key_value_list_stub.extend(key_value_pair.into_iter());
-                        }
-
-                        key_value_list_stub.push(empty_list_as_cell!());
-
-                        functor!(
                             atom!("switch_on_structure"),
-                            [str(orig_h, 0)],
+                            1,
-                            [key_value_list_stub]
+                            structures.iter().map(|((name, arity), ptr)| {
+                                functor!(
+                                    atom!(":"),
+                                    [functor((atom!("/")), [atom_as_cell(name), fixnum((*arity))]),
+                                     indexing_code_ptr((*ptr))]
+                                )
+                            }),
                         )
                     }
                 }
@@ -1133,18 +1110,16 @@ fn generate_instruction_preface() -> TokenStream {
         }
 
         fn arith_instr_unary_functor(
-            h: usize,
             name: Atom,
             arena: &mut Arena,
             at: &ArithmeticTerm,
             t: usize,
         ) -> MachineStub {
             let at_stub = at.into_functor(arena);
-            functor!(name, [str(h, 0), fixnum(t)], [at_stub])
+            functor!(name, [functor(at_stub), fixnum(t)])
         }
 
         fn arith_instr_bin_functor(
-            h: usize,
             name: Atom,
             arena: &mut Arena,
             at_1: &ArithmeticTerm,
@@ -1154,11 +1129,9 @@ fn generate_instruction_preface() -> TokenStream {
             let at_1_stub = at_1.into_functor(arena);
             let at_2_stub = at_2.into_functor(arena);
 
-            functor!(
+            functor!(name, [functor(at_1_stub),
-                name,
+                            functor(at_2_stub),
-                [str(h, 0), str(h, 1), fixnum(t)],
+                            fixnum(t)])
-                [at_1_stub, at_2_stub]
-            )
         }
 
         pub type Code = Vec<Instruction>;
@@ -1170,7 +1143,7 @@ fn generate_instruction_preface() -> TokenStream {
                 match *self {
                     Instruction::GetConstant(_, _, r) => vec![r],
                     Instruction::GetList(_, r) => vec![r],
-                    Instruction::GetPartialString(_, _, r, _) => vec![r],
+                    Instruction::GetPartialString(_, _, r) => vec![r],
                     Instruction::GetStructure(_, _, _, r) => vec![r],
                     Instruction::GetVariable(r, t) => vec![r, temp_v!(t)],
                     Instruction::GetValue(r, t) => vec![r, temp_v!(t)],
@@ -1178,7 +1151,7 @@ fn generate_instruction_preface() -> TokenStream {
                     Instruction::UnifyVariable(r) => vec![r],
                     Instruction::PutConstant(_, _, r) => vec![r],
                     Instruction::PutList(_, r) => vec![r],
-                    Instruction::PutPartialString(_, _, r, _) => vec![r],
+                    Instruction::PutPartialString(_, _, r) => vec![r],
                     Instruction::PutStructure(_, _, r) => vec![r],
                     Instruction::PutValue(r, t) => vec![r, temp_v!(t)],
                     Instruction::PutVariable(r, t) => vec![r, temp_v!(t)],
@@ -1242,7 +1215,6 @@ fn generate_instruction_preface() -> TokenStream {
 
             pub fn enqueue_functors(
                 &self,
-                mut h: usize,
                 arena: &mut Arena,
                 functors: &mut Vec<MachineStub>,
             ) {
@@ -1251,33 +1223,30 @@ fn generate_instruction_preface() -> TokenStream {
                         for indexing_instr in indexing_instrs {
                             match indexing_instr {
                                 IndexingLine::Indexing(indexing_instr) => {
-                                    let section = indexing_instr.to_functor(h);
+                                    let section = indexing_instr.to_functor();
-                                    h += section.len();
                                     functors.push(section);
                                 }
                                 IndexingLine::IndexedChoice(indexed_choice_instrs) => {
                                     for indexed_choice_instr in indexed_choice_instrs {
                                         let section = indexed_choice_instr.to_functor();
-                                        h += section.len();
                                         functors.push(section);
                                     }
                                 }
                                 IndexingLine::DynamicIndexedChoice(indexed_choice_instrs) => {
                                     for indexed_choice_instr in indexed_choice_instrs {
-                                        let section = functor!(atom!("dynamic"), [fixnum(*indexed_choice_instr)]);
+                                        let section = functor!(atom!("dynamic"),
-
+                                                               [fixnum((*indexed_choice_instr))]);
-                                        h += section.len();
                                         functors.push(section);
                                     }
                                 }
                             }
                         }
                     }
-                    instr => functors.push(instr.to_functor(h, arena)),
+                    instr => functors.push(instr.to_functor(arena)),
                 }
             }
 
-            fn to_functor(&self, h: usize, arena: &mut Arena) -> MachineStub {
+            fn to_functor(&self, arena: &mut Arena) -> MachineStub {
                 match self {
                     &Instruction::InstallVerifyAttr => {
                         functor!(atom!("install_verify_attr"))
@@ -1290,25 +1259,23 @@ fn generate_instruction_preface() -> TokenStream {
                             (Death::Infinity, NextOrFail::Next(i)) => {
                                 functor!(
                                     atom!("dynamic_else"),
-                                    [fixnum(birth), atom(atom!("inf")), fixnum(i)]
+                                    [fixnum(birth), atom_as_cell((atom!("inf"))), fixnum(i)]
                                 )
                             }
                             (Death::Infinity, NextOrFail::Fail(i)) => {
-                                let next_functor = functor!(atom!("fail"), [fixnum(i)]);
-
                                 functor!(
                                     atom!("dynamic_else"),
-                                    [fixnum(birth), atom(atom!("inf")), str(h, 0)],
+                                    [fixnum(birth),
-                                    [next_functor]
+                                     atom_as_cell((atom!("inf"))),
+                                     functor((atom!("fail")), [fixnum(i)])]
                                 )
                             }
                             (Death::Finite(d), NextOrFail::Fail(i)) => {
-                                let next_functor = functor!(atom!("fail"), [fixnum(i)]);
-
                                 functor!(
                                     atom!("dynamic_else"),
-                                    [fixnum(birth), fixnum(d), str(h, 0)],
+                                    [fixnum(birth),
-                                    [next_functor]
+                                     fixnum(d),
+                                     functor((atom!("fail")), [fixnum(i)])]
                                 )
                             }
                             (Death::Finite(d), NextOrFail::Next(i)) => {
@@ -1321,25 +1288,23 @@ fn generate_instruction_preface() -> TokenStream {
                             (Death::Infinity, NextOrFail::Next(i)) => {
                                 functor!(
                                     atom!("dynamic_internal_else"),
-                                    [fixnum(birth), atom(atom!("inf")), fixnum(i)]
+                                    [fixnum(birth), atom_as_cell((atom!("inf"))), fixnum(i)]
                                 )
                             }
                             (Death::Infinity, NextOrFail::Fail(i)) => {
-                                let next_functor = functor!(atom!("fail"), [fixnum(i)]);
-
                                 functor!(
                                     atom!("dynamic_internal_else"),
-                                    [fixnum(birth), atom(atom!("inf")), str(h, 0)],
+                                    [fixnum(birth),
-                                    [next_functor]
+                                     atom_as_cell((atom!("inf"))),
+                                     functor((atom!("fail")), [fixnum(i)])]
                                 )
                             }
                             (Death::Finite(d), NextOrFail::Fail(i)) => {
-                                let next_functor = functor!(atom!("fail"), [fixnum(i)]);
-
                                 functor!(
                                     atom!("dynamic_internal_else"),
-                                    [fixnum(birth), fixnum(d), str(h, 0)],
+                                    [fixnum(birth),
-                                    [next_functor]
+                                     fixnum(d),
+                                     functor((atom!("fail")), [fixnum(i)])]
                                 )
                             }
                             (Death::Finite(d), NextOrFail::Next(i)) => {
@@ -1367,157 +1332,154 @@ fn generate_instruction_preface() -> TokenStream {
                     }
                     &Instruction::Cut(r) => {
                         let rt_stub = reg_type_into_functor(r);
-                        functor!(atom!("cut"), [str(h, 0)], [rt_stub])
+                        functor!(atom!("cut"), [functor(rt_stub)])
                     }
                     &Instruction::CutPrev(r) => {
                         let rt_stub = reg_type_into_functor(r);
-                        functor!(atom!("cut_prev"), [str(h, 0)], [rt_stub])
+                        functor!(atom!("cut_prev"), [functor(rt_stub)])
                     }
                     &Instruction::GetLevel(r) => {
                         let rt_stub = reg_type_into_functor(r);
-                        functor!(atom!("get_level"), [str(h, 0)], [rt_stub])
+                        functor!(atom!("get_level"), [functor(rt_stub)])
                     }
                     &Instruction::GetPrevLevel(r) => {
                         let rt_stub = reg_type_into_functor(r);
-                        functor!(atom!("get_prev_level"), [str(h, 0)], [rt_stub])
+                        functor!(atom!("get_prev_level"), [functor(rt_stub)])
                     }
                     &Instruction::GetCutPoint(r) => {
                         let rt_stub = reg_type_into_functor(r);
-                        functor!(atom!("get_cut_point"), [str(h, 0)], [rt_stub])
+                        functor!(atom!("get_cut_point"), [functor(rt_stub)])
                     }
                     &Instruction::NeckCut => {
                         functor!(atom!("neck_cut"))
                     }
                     &Instruction::Add(ref at_1, ref at_2, t) => {
-                        arith_instr_bin_functor(h, atom!("add"), arena, at_1, at_2, t)
+                        arith_instr_bin_functor(atom!("add"), arena, at_1, at_2, t)
                     }
                     &Instruction::Sub(ref at_1, ref at_2, t) => {
-                        arith_instr_bin_functor(h, atom!("sub"), arena, at_1, at_2, t)
+                        arith_instr_bin_functor(atom!("sub"), arena, at_1, at_2, t)
                     }
                     &Instruction::Mul(ref at_1, ref at_2, t) => {
-                        arith_instr_bin_functor(h, atom!("mul"), arena, at_1, at_2, t)
+                        arith_instr_bin_functor(atom!("mul"), arena, at_1, at_2, t)
                     }
                     &Instruction::IntPow(ref at_1, ref at_2, t) => {
-                        arith_instr_bin_functor(h, atom!("int_pow"), arena, at_1, at_2, t)
+                        arith_instr_bin_functor(atom!("int_pow"), arena, at_1, at_2, t)
                     }
                     &Instruction::Pow(ref at_1, ref at_2, t) => {
-                        arith_instr_bin_functor(h, atom!("pow"), arena, at_1, at_2, t)
+                        arith_instr_bin_functor(atom!("pow"), arena, at_1, at_2, t)
                     }
                     &Instruction::IDiv(ref at_1, ref at_2, t) => {
-                        arith_instr_bin_functor(h, atom!("idiv"), arena, at_1, at_2, t)
+                        arith_instr_bin_functor(atom!("idiv"), arena, at_1, at_2, t)
                     }
                     &Instruction::Max(ref at_1, ref at_2, t) => {
-                        arith_instr_bin_functor(h, atom!("max"), arena, at_1, at_2, t)
+                        arith_instr_bin_functor(atom!("max"), arena, at_1, at_2, t)
                     }
                     &Instruction::Min(ref at_1, ref at_2, t) => {
-                        arith_instr_bin_functor(h, atom!("min"), arena, at_1, at_2, t)
+                        arith_instr_bin_functor(atom!("min"), arena, at_1, at_2, t)
                     }
                     &Instruction::IntFloorDiv(ref at_1, ref at_2, t) => {
-                        arith_instr_bin_functor(h, atom!("int_floor_div"), arena, at_1, at_2, t)
+                        arith_instr_bin_functor(atom!("int_floor_div"), arena, at_1, at_2, t)
                     }
                     &Instruction::RDiv(ref at_1, ref at_2, t) => {
-                        arith_instr_bin_functor(h, atom!("rdiv"), arena, at_1, at_2, t)
+                        arith_instr_bin_functor(atom!("rdiv"), arena, at_1, at_2, t)
                     }
                     &Instruction::Div(ref at_1, ref at_2, t) => {
-                        arith_instr_bin_functor(h, atom!("div"), arena, at_1, at_2, t)
+                        arith_instr_bin_functor(atom!("div"), arena, at_1, at_2, t)
                     }
                     &Instruction::Shl(ref at_1, ref at_2, t) => {
-                        arith_instr_bin_functor(h, atom!("shl"), arena, at_1, at_2, t)
+                        arith_instr_bin_functor(atom!("shl"), arena, at_1, at_2, t)
                     }
                     &Instruction::Shr(ref at_1, ref at_2, t) => {
-                        arith_instr_bin_functor(h, atom!("shr"), arena, at_1, at_2, t)
+                        arith_instr_bin_functor(atom!("shr"), arena, at_1, at_2, t)
                     }
                     &Instruction::Xor(ref at_1, ref at_2, t) => {
-                        arith_instr_bin_functor(h, atom!("xor"), arena, at_1, at_2, t)
+                        arith_instr_bin_functor(atom!("xor"), arena, at_1, at_2, t)
                     }
                     &Instruction::And(ref at_1, ref at_2, t) => {
-                        arith_instr_bin_functor(h, atom!("and"), arena, at_1, at_2, t)
+                        arith_instr_bin_functor(atom!("and"), arena, at_1, at_2, t)
                     }
                     &Instruction::Or(ref at_1, ref at_2, t) => {
-                        arith_instr_bin_functor(h, atom!("or"), arena, at_1, at_2, t)
+                        arith_instr_bin_functor(atom!("or"), arena, at_1, at_2, t)
                     }
                     &Instruction::Mod(ref at_1, ref at_2, t) => {
-                        arith_instr_bin_functor(h, atom!("mod"), arena, at_1, at_2, t)
+                        arith_instr_bin_functor(atom!("mod"), arena, at_1, at_2, t)
                     }
                     &Instruction::Rem(ref at_1, ref at_2, t) => {
-                        arith_instr_bin_functor(h, atom!("rem"), arena, at_1, at_2, t)
+                        arith_instr_bin_functor(atom!("rem"), arena, at_1, at_2, t)
                     }
                     &Instruction::ATan2(ref at_1, ref at_2, t) => {
-                        arith_instr_bin_functor(h, atom!("rem"), arena, at_1, at_2, t)
+                        arith_instr_bin_functor(atom!("rem"), arena, at_1, at_2, t)
                     }
                     &Instruction::Gcd(ref at_1, ref at_2, t) => {
-                        arith_instr_bin_functor(h, atom!("gcd"), arena, at_1, at_2, t)
+                        arith_instr_bin_functor(atom!("gcd"), arena, at_1, at_2, t)
                     }
                     &Instruction::Sign(ref at, t) => {
-                        arith_instr_unary_functor(h, atom!("sign"), arena, at, t)
+                        arith_instr_unary_functor(atom!("sign"), arena, at, t)
                     }
                     &Instruction::Cos(ref at, t) => {
-                        arith_instr_unary_functor(h, atom!("cos"), arena, at, t)
+                        arith_instr_unary_functor(atom!("cos"), arena, at, t)
                     }
                     &Instruction::Sin(ref at, t) => {
-                        arith_instr_unary_functor(h, atom!("sin"), arena, at, t)
+                        arith_instr_unary_functor(atom!("sin"), arena, at, t)
                     }
                     &Instruction::Tan(ref at, t) => {
-                        arith_instr_unary_functor(h, atom!("tan"), arena, at, t)
+                        arith_instr_unary_functor(atom!("tan"), arena, at, t)
                     }
                     &Instruction::Log(ref at, t) => {
-                        arith_instr_unary_functor(h, atom!("log"), arena, at, t)
+                        arith_instr_unary_functor(atom!("log"), arena, at, t)
                     }
                     &Instruction::Exp(ref at, t) => {
-                        arith_instr_unary_functor(h, atom!("exp"), arena, at, t)
+                        arith_instr_unary_functor(atom!("exp"), arena, at, t)
                     }
                     &Instruction::ACos(ref at, t) => {
-                        arith_instr_unary_functor(h, atom!("acos"), arena, at, t)
+                        arith_instr_unary_functor(atom!("acos"), arena, at, t)
                     }
                     &Instruction::ASin(ref at, t) => {
-                        arith_instr_unary_functor(h, atom!("asin"), arena, at, t)
+                        arith_instr_unary_functor(atom!("asin"), arena, at, t)
                     }
                     &Instruction::ATan(ref at, t) => {
-                        arith_instr_unary_functor(h, atom!("atan"), arena, at, t)
+                        arith_instr_unary_functor(atom!("atan"), arena, at, t)
                     }
                     &Instruction::Sqrt(ref at, t) => {
-                        arith_instr_unary_functor(h, atom!("sqrt"), arena, at, t)
+                        arith_instr_unary_functor(atom!("sqrt"), arena, at, t)
                     }
                     &Instruction::Abs(ref at, t) => {
-                        arith_instr_unary_functor(h, atom!("abs"), arena, at, t)
+                        arith_instr_unary_functor(atom!("abs"), arena, at, t)
                     }
                     &Instruction::Float(ref at, t) => {
-                        arith_instr_unary_functor(h, atom!("float"), arena, at, t)
+                        arith_instr_unary_functor(atom!("float"), arena, at, t)
                     }
                     &Instruction::Truncate(ref at, t) => {
-                        arith_instr_unary_functor(h, atom!("truncate"), arena, at, t)
+                        arith_instr_unary_functor(atom!("truncate"), arena, at, t)
                     }
                     &Instruction::Round(ref at, t) => {
-                        arith_instr_unary_functor(h, atom!("round"), arena, at, t)
+                        arith_instr_unary_functor(atom!("round"), arena, at, t)
                     }
                     &Instruction::Ceiling(ref at, t) => {
-                        arith_instr_unary_functor(h, atom!("ceiling"), arena, at, t)
+                        arith_instr_unary_functor(atom!("ceiling"), arena, at, t)
                     }
                     &Instruction::Floor(ref at, t) => {
-                        arith_instr_unary_functor(h, atom!("floor"), arena, at, t)
+                        arith_instr_unary_functor(atom!("floor"), arena, at, t)
                     }
                     &Instruction::FloatFractionalPart(ref at, t) => {
-                        arith_instr_unary_functor(h, atom!("float_fractional_part"), arena, at, t)
+                        arith_instr_unary_functor(atom!("float_fractional_part"), arena, at, t)
                     }
                     &Instruction::FloatIntegerPart(ref at, t) => {
-                        arith_instr_unary_functor(h, atom!("float_integer_part"), arena, at, t)
+                        arith_instr_unary_functor(atom!("float_integer_part"), arena, at, t)
                     }
                     &Instruction::Neg(ref at, t) => arith_instr_unary_functor(
-                        h,
                         atom!("-"),
                         arena,
                         at,
                         t,
                     ),
                     &Instruction::Plus(ref at, t) => arith_instr_unary_functor(
-                        h,
                         atom!("+"),
                         arena,
                         at,
                         t,
                     ),
                     &Instruction::BitwiseComplement(ref at, t) => arith_instr_unary_functor(
-                        h,
                         atom!("\\"),
                         arena,
                         at,
@@ -1533,16 +1495,16 @@ fn generate_instruction_preface() -> TokenStream {
                         functor!(atom!("allocate"), [fixnum(num_frames)])
                     }
                     &Instruction::CallNamed(arity, name, ..) => {
-                        functor!(atom!("call"), [atom(name), fixnum(arity)])
+                        functor!(atom!("call"), [atom_as_cell(name), fixnum(arity)])
                     }
                     &Instruction::ExecuteNamed(arity, name, ..) => {
-                        functor!(atom!("execute"), [atom(name), fixnum(arity)])
+                        functor!(atom!("execute"), [atom_as_cell(name), fixnum(arity)])
                     }
                     &Instruction::DefaultCallNamed(arity, name, ..) => {
-                        functor!(atom!("call_default"), [atom(name), fixnum(arity)])
+                        functor!(atom!("call_default"), [atom_as_cell(name), fixnum(arity)])
                     }
                     &Instruction::DefaultExecuteNamed(arity, name, ..) => {
-                        functor!(atom!("execute_default"), [atom(name), fixnum(arity)])
+                        functor!(atom!("execute_default"), [atom_as_cell(name), fixnum(arity)])
                     }
                     &Instruction::CallN(arity) => {
                         functor!(atom!("call_n"), [fixnum(arity)])
@@ -1585,7 +1547,7 @@ fn generate_instruction_preface() -> TokenStream {
                     &Instruction::CallSort |
                     &Instruction::CallGetNumber(_) => {
                         let (name, arity) = self.to_name_and_arity();
-                        functor!(atom!("call"), [atom(name), fixnum(arity)])
+                        functor!(atom!("call"), [atom_as_cell(name), fixnum(arity)])
                     }
                     //
                     &Instruction::ExecuteTermGreaterThan |
@@ -1611,7 +1573,7 @@ fn generate_instruction_preface() -> TokenStream {
                     &Instruction::ExecuteSort |
                     &Instruction::ExecuteGetNumber(_) => {
                         let (name, arity) = self.to_name_and_arity();
-                        functor!(atom!("execute"), [atom(name), fixnum(arity)])
+                        functor!(atom!("execute"), [atom_as_cell(name), fixnum(arity)])
                     }
                     //
                     &Instruction::DefaultCallTermGreaterThan |
@@ -1637,7 +1599,7 @@ fn generate_instruction_preface() -> TokenStream {
                     &Instruction::DefaultCallSort |
                     &Instruction::DefaultCallGetNumber(_) => {
                         let (name, arity) = self.to_name_and_arity();
-                        functor!(atom!("call_default"), [atom(name), fixnum(arity)])
+                        functor!(atom!("call_default"), [atom_as_cell(name), fixnum(arity)])
                     }
                     //
                     &Instruction::DefaultExecuteTermGreaterThan |
@@ -1663,7 +1625,7 @@ fn generate_instruction_preface() -> TokenStream {
                     &Instruction::DefaultExecuteSort |
                     &Instruction::DefaultExecuteGetNumber(_) => {
                         let (name, arity) = self.to_name_and_arity();
-                        functor!(atom!("execute_default"), [atom(name), fixnum(arity)])
+                        functor!(atom!("execute_default"), [atom_as_cell(name), fixnum(arity)])
                     }
                     &Instruction::CallIsAtom(r) |
                     &Instruction::CallIsAtomic(r) |
@@ -1676,7 +1638,8 @@ fn generate_instruction_preface() -> TokenStream {
                     &Instruction::CallIsVar(r) => {
                         let (name, arity) = self.to_name_and_arity();
                         let rt_stub = reg_type_into_functor(r);
-                        functor!(atom!("call"), [atom(name), fixnum(arity), str(h, 0)], [rt_stub])
+
+                        functor!(atom!("call"), [atom_as_cell(name), fixnum(arity), functor(rt_stub)])
                     }
                     &Instruction::ExecuteIsAtom(r) |
                     &Instruction::ExecuteIsAtomic(r) |
@@ -1689,7 +1652,8 @@ fn generate_instruction_preface() -> TokenStream {
                     &Instruction::ExecuteIsVar(r) => {
                         let (name, arity) = self.to_name_and_arity();
                         let rt_stub = reg_type_into_functor(r);
-                        functor!(atom!("execute"), [atom(name), fixnum(arity), str(h, 0)], [rt_stub])
+
+                        functor!(atom!("execute"), [atom_as_cell(name), fixnum(arity), functor(rt_stub)])
                     }
                     //
                     &Instruction::CallAtomChars |
@@ -1871,6 +1835,11 @@ fn generate_instruction_preface() -> TokenStream {
                     &Instruction::CallSetEnv |
                     &Instruction::CallUnsetEnv |
                     &Instruction::CallShell |
+                    &Instruction::CallProcessCreate |
+                    &Instruction::CallProcessId |
+                    &Instruction::CallProcessWait |
+                    &Instruction::CallProcessKill |
+                    &Instruction::CallProcessRelease |
                     &Instruction::CallPid |
                     &Instruction::CallCharsBase64 |
                     &Instruction::CallDevourWhitespace |
@@ -1920,14 +1889,14 @@ fn generate_instruction_preface() -> TokenStream {
                     &Instruction::CallEd25519VerifyRaw |
                     &Instruction::CallEd25519SeedToPublicKey => {
                         let (name, arity) = self.to_name_and_arity();
-                        functor!(atom!("call"), [atom(name), fixnum(arity)])
+                        functor!(atom!("call"), [atom_as_cell(name), fixnum(arity)])
                     }
                     //
                     #[cfg(feature = "crypto-full")]
                     &Instruction::CallCryptoDataEncrypt |
                     &Instruction::CallCryptoDataDecrypt => {
                         let (name, arity) = self.to_name_and_arity();
-                        functor!(atom!("call"), [atom(name), fixnum(arity)])
+                        functor!(atom!("call"), [atom_as_cell(name), fixnum(arity)])
                     }
                     //
                     &Instruction::ExecuteAtomChars |
@@ -2109,6 +2078,11 @@ fn generate_instruction_preface() -> TokenStream {
                     &Instruction::ExecuteSetEnv |
                     &Instruction::ExecuteUnsetEnv |
                     &Instruction::ExecuteShell |
+                    &Instruction::ExecuteProcessCreate |
+                    &Instruction::ExecuteProcessId |
+                    &Instruction::ExecuteProcessWait |
+                    &Instruction::ExecuteProcessKill |
+                    &Instruction::ExecuteProcessRelease |
                     &Instruction::ExecutePid |
                     &Instruction::ExecuteCharsBase64 |
                     &Instruction::ExecuteDevourWhitespace |
@@ -2158,14 +2132,14 @@ fn generate_instruction_preface() -> TokenStream {
                     &Instruction::ExecuteEd25519VerifyRaw |
                     &Instruction::ExecuteEd25519SeedToPublicKey => {
                         let (name, arity) = self.to_name_and_arity();
-                        functor!(atom!("execute"), [atom(name), fixnum(arity)])
+                        functor!(atom!("execute"), [atom_as_cell(name), fixnum(arity)])
                     }
                     //
                     #[cfg(feature = "crypto-full")]
                     &Instruction::ExecuteCryptoDataEncrypt |
                     &Instruction::ExecuteCryptoDataDecrypt => {
                         let (name, arity) = self.to_name_and_arity();
-                        functor!(atom!("execute"), [atom(name), fixnum(arity)])
+                        functor!(atom!("execute"), [atom_as_cell(name), fixnum(arity)])
                     }
                     //
                     &Instruction::Deallocate => {
@@ -2180,73 +2154,60 @@ fn generate_instruction_preface() -> TokenStream {
                     &Instruction::Proceed => {
                         functor!(atom!("proceed"))
                     }
-                    &Instruction::GetConstant(lvl, c, r) => {
+                    &Instruction::GetConstant(lvl, lit, r) => {
                         let lvl_stub = lvl.into_functor();
                         let rt_stub = reg_type_into_functor(r);
 
-                        functor!(
+                        functor!(atom!("get_constant"), [functor(lvl_stub),
-                            atom!("get_constant"),
+                                                         cell(lit),
-                            [str(h, 0), cell(c), str(h, 1)],
+                                                         functor(rt_stub)])
-                            [lvl_stub, rt_stub]
-                        )
                     }
                     &Instruction::GetList(lvl, r) => {
                         let lvl_stub = lvl.into_functor();
                         let rt_stub = reg_type_into_functor(r);
 
-                        functor!(
+                        functor!(atom!("get_list"), [functor(lvl_stub), functor(rt_stub)])
-                            atom!("get_list"),
-                            [str(h, 0), str(h, 1)],
-                            [lvl_stub, rt_stub]
-                        )
                     }
-                    &Instruction::GetPartialString(lvl, s, r, has_tail) => {
+                    &Instruction::GetPartialString(lvl, ref s, r) => {
                         let lvl_stub = lvl.into_functor();
                         let rt_stub = reg_type_into_functor(r);
 
-                        functor!(
+                        functor!(atom!("get_partial_string"), [functor(lvl_stub),
-                            atom!("get_partial_string"),
+                                                               string((s.to_string())),
-                            [
+                                                               functor(rt_stub)])
-                                str(h, 0),
-                                string(h, s),
-                                str(h, 1),
-                                boolean(has_tail)
-                            ],
-                            [lvl_stub, rt_stub]
-                        )
                     }
                     &Instruction::GetStructure(lvl, name, arity, r) => {
                         let lvl_stub = lvl.into_functor();
                         let rt_stub = reg_type_into_functor(r);
 
-                        functor!(
+                        functor!(atom!("get_structure"), [functor(lvl_stub),
-                            atom!("get_structure"),
+                                                          atom_as_cell(name),
-                            [str(h, 0), atom(name), fixnum(arity), str(h, 1)],
+                                                          fixnum(arity),
-                            [lvl_stub, rt_stub]
+                                                          functor(rt_stub)])
-                        )
                     }
                     &Instruction::GetValue(r, arg) => {
                         let rt_stub = reg_type_into_functor(r);
-                        functor!(atom!("get_value"), [str(h, 0), fixnum(arg)], [rt_stub])
+                        functor!(atom!("get_value"), [functor(rt_stub),
+                                                      fixnum(arg)])
                     }
                     &Instruction::GetVariable(r, arg) => {
                         let rt_stub = reg_type_into_functor(r);
-                        functor!(atom!("get_variable"), [str(h, 0), fixnum(arg)], [rt_stub])
+                        functor!(atom!("get_variable"), [functor(rt_stub), fixnum(arg)])
                     }
                     &Instruction::UnifyConstant(c) => {
                         functor!(atom!("unify_constant"), [cell(c)])
                     }
                     &Instruction::UnifyLocalValue(r) => {
                         let rt_stub = reg_type_into_functor(r);
-                        functor!(atom!("unify_local_value"), [str(h, 0)], [rt_stub])
+                        functor!(atom!("unify_local_value"), [functor(rt_stub)])
                     }
                     &Instruction::UnifyVariable(r) => {
                         let rt_stub = reg_type_into_functor(r);
-                        functor!(atom!("unify_variable"), [str(h, 0)], [rt_stub])
+                        functor!(atom!("unify_variable"), [functor(rt_stub)])
                     }
                     &Instruction::UnifyValue(r) => {
                         let rt_stub = reg_type_into_functor(r);
-                        functor!(atom!("unify_value"), [str(h, 0)], [rt_stub])
+                        functor!(atom!("unify_value"), [functor(rt_stub)])
                     }
                     &Instruction::UnifyVoid(vars) => {
                         functor!(atom!("unify_void"), [fixnum(vars)])
@@ -2258,68 +2219,55 @@ fn generate_instruction_preface() -> TokenStream {
                         let lvl_stub = lvl.into_functor();
                         let rt_stub = reg_type_into_functor(r);
 
-                        functor!(
+                        functor!(atom!("put_constant"), [functor(rt_stub), cell(c), functor(lvl_stub)])
-                            atom!("put_constant"),
-                            [str(h, 0), cell(c), str(h, 1)],
-                            [lvl_stub, rt_stub]
-                        )
                     }
                     &Instruction::PutList(lvl, r) => {
                         let lvl_stub = lvl.into_functor();
                         let rt_stub = reg_type_into_functor(r);
 
-                        functor!(
+                        functor!(atom!("put_list"), [functor(lvl_stub), functor(rt_stub)])
-                            atom!("put_list"),
-                            [str(h, 0), str(h, 1)],
-                            [lvl_stub, rt_stub]
-                        )
                     }
-                    &Instruction::PutPartialString(lvl, s, r, has_tail) => {
+                    &Instruction::PutPartialString(lvl, ref s, r) => {
                         let lvl_stub = lvl.into_functor();
                         let rt_stub = reg_type_into_functor(r);
 
-                        functor!(
+                        functor!(atom!("put_partial_string"), [functor(lvl_stub),
-                            atom!("put_partial_string"),
+                                                               string((s.to_string())),
-                            [
+                                                               functor(rt_stub)])
-                                str(h, 0),
-                                string(h, s),
-                                str(h, 1),
-                                boolean(has_tail)
-                            ],
-                            [lvl_stub, rt_stub]
-                        )
                     }
                     &Instruction::PutStructure(name, arity, r) => {
                         let rt_stub = reg_type_into_functor(r);
 
-                        functor!(
+                        functor!(atom!("put_structure"), [atom_as_cell(name),
-                            atom!("put_structure"),
+                                                          fixnum(arity),
-                            [atom(name), fixnum(arity), str(h, 0)],
+                                                          functor(rt_stub)])
-                            [rt_stub]
-                        )
                     }
                     &Instruction::PutValue(r, arg) => {
                         let rt_stub = reg_type_into_functor(r);
-                        functor!(atom!("put_value"), [str(h, 0), fixnum(arg)], [rt_stub])
+
+                        functor!(atom!("put_value"), [functor(rt_stub),
+                                                      fixnum(arg)])
                     }
                     &Instruction::PutVariable(r, arg) => {
                         let rt_stub = reg_type_into_functor(r);
-                        functor!(atom!("put_variable"), [str(h, 0), fixnum(arg)], [rt_stub])
+
+                        functor!(atom!("put_variable"), [functor(rt_stub),
+                                                         fixnum(arg)])
                     }
                     &Instruction::SetConstant(c) => {
                         functor!(atom!("set_constant"), [cell(c)])
                     }
                     &Instruction::SetLocalValue(r) => {
                         let rt_stub = reg_type_into_functor(r);
-                        functor!(atom!("set_local_value"), [str(h, 0)], [rt_stub])
+                        functor!(atom!("set_local_value"), [functor(rt_stub)])
                     }
                     &Instruction::SetVariable(r) => {
                         let rt_stub = reg_type_into_functor(r);
-                        functor!(atom!("set_variable"), [str(h, 0)], [rt_stub])
+                        functor!(atom!("set_variable"), [functor(rt_stub)])
                     }
                     &Instruction::SetValue(r) => {
                         let rt_stub = reg_type_into_functor(r);
-                        functor!(atom!("set_value"), [str(h, 0)], [rt_stub])
+                        functor!(atom!("set_value"), [functor(rt_stub)])
                     }
                     &Instruction::SetVoid(vars) => {
                         functor!(atom!("set_void"), [fixnum(vars)])
@@ -2770,7 +2718,7 @@ pub fn generate_instructions_rs() -> TokenStream {
 
         if ident == "Named" {
             clause_type_from_name_and_arity_arms.push(quote! {
-                (name, arity) => ClauseType::Named(arity, name, CodeIndex::default(arena))
+                (name, arity) => ClauseType::Named(arity, name, CodeIndex::default(&mut arena.code_index_tbl))
             });
 
             clause_type_to_instr_arms.push(quote! {
@@ -3198,12 +3146,6 @@ pub fn generate_instructions_rs() -> TokenStream {
                 }
             }
 
-            pub fn is_inbuilt(name: Atom, arity: usize) -> bool {
-                matches!((name, arity),
-                    #(#is_inbuilt_arms)|*
-                )
-            }
-
             pub fn name(&self) -> Atom {
                 match self {
                     #(
@@ -3212,6 +3154,12 @@ pub fn generate_instructions_rs() -> TokenStream {
                 }
             }
 
+            pub fn is_inbuilt(name: Atom, arity: usize) -> bool {
+                matches!((name, arity),
+                    #(#is_inbuilt_arms)|*
+                )
+            }
+
             pub fn is_inlined(name: Atom, arity: usize) -> bool {
                 matches!((name, arity),
                     #(#is_inlined_arms)|*
@@ -3334,14 +3282,14 @@ where
     let disc = match DiscriminantT::from_str(id.to_string().as_str()) {
         Ok(disc) => disc,
         Err(_) => {
-            panic!("can't generate discriminant {}", id);
+            panic!("can't generate discriminant {id}");
         }
     };
 
     match disc.get_str(key) {
         Some(prop) => prop,
         None => {
-            panic!("can't find property {} of discriminant {:?}", key, disc);
+            panic!("can't find property {key} of discriminant {disc:?}");
         }
     }
 }
@@ -3459,7 +3407,7 @@ impl InstructionData {
 
             (name, arity, CountableInference::HasDefault)
         } else {
-            panic!("type ID is: {}", id);
+            panic!("type ID is: {id}");
         };
 
         let v_ident = variant

build/static_string_indexing.rs

@@ -84,6 +84,18 @@ impl<'ast> Visit<'ast> for StaticStrVisitor {
     }
 }
 
+const INLINED_ATOM_MAX_LEN: usize = 6;
+
+fn static_string_index(string: &str, index: usize) -> u64 {
+    if !string.is_empty() && string.len() <= INLINED_ATOM_MAX_LEN && !string.contains('\u{0}') {
+        let mut string_buf: [u8; 8] = [0u8; 8];
+        string_buf[..string.len()].copy_from_slice(string.as_bytes());
+        (u64::from_le_bytes(string_buf) << 1) | 1
+    } else {
+        (index << 1) as u64
+    }
+}
+
 pub fn index_static_strings(instruction_rs_path: &std::path::Path) -> TokenStream {
     use quote::*;
 
@@ -114,14 +126,14 @@ pub fn index_static_strings(instruction_rs_path: &std::path::Path) -> TokenStrea
         match file.read_to_string(&mut src) {
             Ok(_) => {}
             Err(e) => {
-                panic!("error reading file: {:?}", e);
+                panic!("error reading file: {e:?}");
             }
         }
 
         let syntax = match syn::parse_file(&src) {
             Ok(s) => s,
             Err(e) => {
-                panic!("parse error: {} in file {:?}", e, path);
+                panic!("parse error: {e} in file {path:?}");
             }
         };
         Ok(syntax)
@@ -149,11 +161,29 @@ pub fn index_static_strings(instruction_rs_path: &std::path::Path) -> TokenStrea
         visitor.visit_file(&syntax)
     }
 
-    let indices = (0..visitor.static_strs.len()).map(|i| (i << 3) as u64);
+    let mut static_str_keys = vec![];
-    let indices_iter = indices.clone();
+    let mut static_strs = vec![];
+    let mut static_str_indices = vec![];
 
-    let static_strs_len = visitor.static_strs.len();
+    let indices: Vec<u64> = visitor
-    let static_strs: &Vec<_> = &visitor.static_strs.into_iter().collect();
+        .static_strs
+        .iter()
+        .map(|string| {
+            let index = static_string_index(string, static_strs.len());
+
+            static_str_keys.push(string);
+
+            if index & 1 == 1 {
+                index
+            } else {
+                static_str_indices.push(index);
+                static_strs.push(string);
+                index
+            }
+        })
+        .collect();
+
+    let static_strs_len = static_strs.len();
 
     quote! {
         static STRINGS: [&str; #static_strs_len] = [
@@ -163,11 +193,12 @@ pub fn index_static_strings(instruction_rs_path: &std::path::Path) -> TokenStrea
         ];
 
         macro_rules! atom {
-            #((#static_strs) => { Atom { index: #indices_iter } };)*
+            #((#static_str_keys) => { Atom { index: #indices } };)*
+            ($name:literal) => {compile_error!(concat!("unknown static atom ", $name))};
         }
 
         pub static STATIC_ATOMS_MAP: phf::Map<&'static str, Atom> = phf::phf_map! {
-            #(#static_strs => { Atom { index: #indices } },)*
+            #(#static_strs => { Atom { index: #static_str_indices } },)*
         };
     }
 }

src/allocator.rs

@@ -14,7 +14,7 @@ pub(crate) trait Allocator {
         lvl: Level,
         context: GenContext,
         code: &mut CodeDeque,
-    );
+    ) -> RegType;
 
     fn mark_non_var<'a, Target: CompilationTarget<'a>>(
         &mut self,

src/arena.rs

@@ -3,31 +3,27 @@
 #[cfg(feature = "http")]
 use crate::http::{HttpListener, HttpResponse};
 use crate::machine::loader::LiveLoadState;
-use crate::machine::machine_indices::*;
 use crate::machine::streams::*;
-use crate::raw_block::*;
+use crate::offset_table::*;
 use crate::read::*;
 use crate::types::UntypedArenaPtr;
 
 use crate::parser::dashu::{Integer, Rational};
-use arcu::atomic::Arcu;
-use arcu::epoch_counters::GlobalEpochCounterPool;
-use arcu::rcu_ref::RcuRef;
-use arcu::Rcu;
 use ordered_float::OrderedFloat;
 
-use std::cell::UnsafeCell;
 use std::fmt;
 use std::fmt::Debug;
 use std::hash::{Hash, Hasher};
+use std::io::PipeReader;
+use std::io::PipeWriter;
 use std::mem;
 use std::mem::ManuallyDrop;
 use std::net::TcpListener;
 use std::ops::{Deref, DerefMut};
+use std::process::Child;
 use std::ptr;
 use std::ptr::addr_of_mut;
 use std::ptr::NonNull;
-use std::sync::RwLock;
 
 macro_rules! arena_alloc {
     ($e:expr, $arena:expr) => {{
@@ -38,8 +34,7 @@ macro_rules! arena_alloc {
 
 macro_rules! float_alloc {
     ($e:expr, $arena:expr) => {{
-        let result = $e;
+        $arena.f64_tbl.build_with(OrderedFloat($e))
-        unsafe { $arena.f64_tbl.build_with(result).as_ptr() }
     }};
 }
 
@@ -55,120 +50,6 @@ where
     payload_offset - header_offset
 }
 
-use std::sync::Arc;
-use std::sync::Mutex;
-use std::sync::Weak;
-
-const F64_TABLE_INIT_SIZE: usize = 1 << 16;
-const F64_TABLE_ALIGN: usize = 8;
-
-#[inline(always)]
-fn global_f64table() -> &'static RwLock<Weak<F64Table>> {
-    static GLOBAL_ATOM_TABLE: RwLock<Weak<F64Table>> = RwLock::new(Weak::new());
-    &GLOBAL_ATOM_TABLE
-}
-
-impl RawBlockTraits for F64Table {
-    #[inline]
-    fn init_size() -> usize {
-        F64_TABLE_INIT_SIZE
-    }
-
-    #[inline]
-    fn align() -> usize {
-        F64_TABLE_ALIGN
-    }
-}
-
-#[derive(Debug)]
-pub struct F64Table {
-    block: Arcu<RawBlock<F64Table>, GlobalEpochCounterPool>,
-    update: Mutex<()>,
-}
-
-// TODO: Actually prove this, as it's probably unsound right now
-unsafe impl Send for F64Table {}
-unsafe impl Sync for F64Table {}
-
-#[inline(always)]
-pub fn lookup_float(
-    offset: F64Offset,
-) -> RcuRef<RawBlock<F64Table>, UnsafeCell<OrderedFloat<f64>>> {
-    let f64table = global_f64table()
-        .read()
-        .unwrap()
-        .upgrade()
-        .expect("We should only be looking up floats while there is a float table");
-
-    RcuRef::try_map(f64table.block.read(), |raw_block| unsafe {
-        raw_block
-            .base
-            .add(offset.0)
-            .cast_mut()
-            .cast::<UnsafeCell<OrderedFloat<f64>>>()
-            .as_ref()
-    })
-    .expect("The offset should result in a non-null pointer")
-}
-
-impl F64Table {
-    #[inline]
-    pub fn new() -> Arc<Self> {
-        let upgraded = global_f64table().read().unwrap().upgrade();
-        // don't inline upgraded, otherwise temporary will be dropped too late in case of None
-        if let Some(atom_table) = upgraded {
-            atom_table
-        } else {
-            let mut guard = global_f64table().write().unwrap();
-            // try to upgrade again in case we lost the race on the write lock
-            if let Some(atom_table) = guard.upgrade() {
-                atom_table
-            } else {
-                let atom_table = Arc::new(Self {
-                    block: Arcu::new(RawBlock::new(), GlobalEpochCounterPool),
-                    update: Mutex::new(()),
-                });
-                *guard = Arc::downgrade(&atom_table);
-                atom_table
-            }
-        }
-    }
-
-    #[allow(clippy::missing_safety_doc)]
-    pub unsafe fn build_with(&self, value: f64) -> F64Offset {
-        let update_guard = self.update.lock();
-
-        // we don't have an index table for lookups as AtomTable does so
-        // just get the epoch after we take the upgrade lock
-        let mut block_epoch = self.block.read();
-
-        let mut ptr;
-
-        loop {
-            ptr = block_epoch.alloc(mem::size_of::<f64>());
-
-            if ptr.is_null() {
-                let new_block = block_epoch.grow_new().unwrap();
-                self.block.replace(new_block);
-                block_epoch = self.block.read();
-            } else {
-                break;
-            }
-        }
-
-        ptr::write(ptr as *mut OrderedFloat<f64>, OrderedFloat(value));
-
-        let float = F64Offset(ptr as usize - block_epoch.base as usize);
-
-        // atometable would have to update the index table at this point
-
-        // expicit drop to ensure we don't accidentally drop it early
-        drop(update_guard);
-
-        float
-    }
-}
-
 #[derive(BitfieldSpecifier, Copy, Clone, Debug, PartialEq)]
 #[bits = 7]
 pub enum ArenaHeaderTag {
@@ -193,11 +74,10 @@ pub enum ArenaHeaderTag {
     TcpListener = 0b1000000,
     HttpListener = 0b1000001,
     HttpResponse = 0b1000010,
+    PipeWriter = 0b1000011,
     Dropped = 0b1000100,
-    IndexPtrDynamicUndefined = 0b1000101,
+    PipeReader = 0b1001001,
-    IndexPtrDynamicIndex = 0b1000110,
+    ChildProcess = 0b1001010,
-    IndexPtrIndex = 0b1000111,
-    IndexPtrUndefined = 0b1001000,
 }
 
 #[bitfield]
@@ -436,137 +316,6 @@ pub trait ArenaAllocated {
     }
 }
 
-#[derive(Debug)]
-pub struct F64Ptr(RcuRef<RawBlock<F64Table>, UnsafeCell<OrderedFloat<f64>>>);
-
-impl Clone for F64Ptr {
-    fn clone(&self) -> Self {
-        Self(RcuRef::clone(&self.0))
-    }
-}
-
-impl PartialEq for F64Ptr {
-    fn eq(&self, other: &F64Ptr) -> bool {
-        RcuRef::ptr_eq(&self.0, &other.0) || self.deref() == other.deref()
-    }
-}
-
-impl Eq for F64Ptr {}
-
-impl PartialOrd for F64Ptr {
-    fn partial_cmp(&self, other: &Self) -> Option<std::cmp::Ordering> {
-        Some(self.cmp(other))
-    }
-}
-
-impl Ord for F64Ptr {
-    fn cmp(&self, other: &Self) -> std::cmp::Ordering {
-        (**self).cmp(&**other)
-    }
-}
-
-impl Hash for F64Ptr {
-    #[inline(always)]
-    fn hash<H: Hasher>(&self, hasher: &mut H) {
-        (self as &OrderedFloat<f64>).hash(hasher)
-    }
-}
-
-impl fmt::Display for F64Ptr {
-    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
-        write!(f, "{}", self as &OrderedFloat<f64>)
-    }
-}
-
-impl Deref for F64Ptr {
-    type Target = OrderedFloat<f64>;
-
-    #[inline]
-    fn deref(&self) -> &Self::Target {
-        unsafe { self.0.get().as_ref().unwrap() }
-    }
-}
-
-impl DerefMut for F64Ptr {
-    #[inline]
-    fn deref_mut(&mut self) -> &mut Self::Target {
-        unsafe { &mut *self.0.get().as_mut().unwrap() }
-    }
-}
-
-impl F64Ptr {
-    #[inline(always)]
-    pub fn from_offset(offset: F64Offset) -> Self {
-        Self(lookup_float(offset))
-    }
-
-    #[inline(always)]
-    pub fn as_offset(&self) -> F64Offset {
-        F64Offset(self.0.get() as usize - RcuRef::get_root(&self.0).base as usize)
-    }
-}
-
-#[derive(Clone, Copy, Debug)]
-pub struct F64Offset(usize);
-
-impl F64Offset {
-    #[inline(always)]
-    pub fn new(offset: usize) -> Self {
-        Self(offset)
-    }
-
-    #[inline(always)]
-    pub fn from_ptr(ptr: F64Ptr) -> Self {
-        ptr.as_offset()
-    }
-
-    #[inline(always)]
-    pub fn as_ptr(self) -> F64Ptr {
-        F64Ptr::from_offset(self)
-    }
-
-    #[inline(always)]
-    pub fn to_u64(self) -> u64 {
-        self.0 as u64
-    }
-}
-
-impl PartialEq for F64Offset {
-    #[inline(always)]
-    fn eq(&self, other: &F64Offset) -> bool {
-        self.as_ptr() == other.as_ptr()
-    }
-}
-
-impl Eq for F64Offset {}
-
-impl PartialOrd for F64Offset {
-    #[inline(always)]
-    fn partial_cmp(&self, other: &Self) -> Option<std::cmp::Ordering> {
-        Some(self.cmp(other))
-    }
-}
-
-impl Ord for F64Offset {
-    #[inline(always)]
-    fn cmp(&self, other: &Self) -> std::cmp::Ordering {
-        self.as_ptr().cmp(&other.as_ptr())
-    }
-}
-
-impl Hash for F64Offset {
-    #[inline(always)]
-    fn hash<H: Hasher>(&self, hasher: &mut H) {
-        self.as_ptr().hash(hasher)
-    }
-}
-
-impl fmt::Display for F64Offset {
-    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
-        write!(f, "F64Offset({})", self.0)
-    }
-}
-
 impl ArenaAllocated for Integer {
     type Payload = Self;
     #[inline]
@@ -644,43 +393,16 @@ impl ArenaAllocated for HttpResponse {
     }
 }
 
-impl ArenaAllocated for IndexPtr {
+impl ArenaAllocated for Child {
-    type Payload = Self;
+    type Payload = ManuallyDrop<Self>;
     #[inline]
     fn tag() -> ArenaHeaderTag {
-        ArenaHeaderTag::IndexPtrUndefined
+        ArenaHeaderTag::ChildProcess
     }
-
+}
-    #[inline]
+impl AllocateInArena<Child> for Child {
-    fn header_offset_from_payload() -> usize {
+    fn arena_allocate(self, arena: &mut Arena) -> TypedArenaPtr<Child> {
-        0
+        Child::alloc(arena, ManuallyDrop::new(self))
-    }
-
-    /// #  Safety
-    /// - the caller must guarantee that the pointee type of UntypedArenaPtr is T
-    /// - the pointer must be non-null
-    unsafe fn typed_ptr(ptr: UntypedArenaPtr) -> TypedArenaPtr<Self> {
-        TypedArenaPtr(NonNull::new_unchecked(
-            ptr.get_ptr().cast_mut().cast::<IndexPtr>(),
-        ))
-    }
-
-    #[inline]
-    fn alloc(arena: &mut Arena, value: Self) -> TypedArenaPtr<Self> {
-        let slab = Box::new(IndexPtrSlab {
-            next: arena.base.take(),
-            index_ptr: value,
-        });
-
-        let (allocated_ptr, untyped_slab) = slab.to_untyped();
-        arena.base = Some(untyped_slab);
-        allocated_ptr
-    }
-
-    /// # Safety
-    /// - ptr points to an allocated slab of the correct kind
-    unsafe fn dealloc(ptr: NonNull<TypedAllocSlab<Self>>) {
-        drop(unsafe { Box::from_raw(ptr.as_ptr().cast::<IndexPtrSlab>()) });
     }
 }
 
@@ -691,13 +413,6 @@ pub struct AllocSlab {
     header: ArenaHeader,
 }
 
-#[repr(C)]
-#[derive(Debug)]
-pub struct IndexPtrSlab {
-    next: Option<UntypedArenaSlab>,
-    index_ptr: IndexPtr,
-}
-
 const _: () = {
     if std::mem::align_of::<AllocSlab>() < std::mem::align_of::<*const ()>() {
         panic!("alignment of AllocSlab is too low");
@@ -706,34 +421,8 @@ const _: () = {
     if std::mem::offset_of!(AllocSlab, header) % std::mem::align_of::<*const ()>() != 0 {
         panic!("alignment of header not a multiple of pointers alignment");
     }
-
-    if std::mem::offset_of!(AllocSlab, header) != std::mem::offset_of!(IndexPtrSlab, index_ptr) {
-        panic!("IndexPtrSlab.index_ptr and AllocSlab.header are at different offsets");
-    }
 };
 
-impl IndexPtrSlab {
-    #[inline]
-    pub fn to_untyped(self: Box<Self>) -> (TypedArenaPtr<IndexPtr>, UntypedArenaSlab) {
-        let raw_box = Box::into_raw(self);
-
-        // safety: the pointer from Box::into_raw fullfills addr_of_mut's saftey requirements
-        let index_ptr_ptr = unsafe { ptr::addr_of_mut!((*raw_box).index_ptr) };
-        let allocated_ptr = TypedArenaPtr(
-            // safety: the pointer points into a valid allocation so it is non null
-            unsafe { NonNull::new_unchecked(index_ptr_ptr) },
-        );
-
-        let untyped_arena = UntypedArenaSlab {
-            // safety: pointer from Box::into_raw is never null
-            slab: unsafe { NonNull::new_unchecked(raw_box.cast::<AllocSlab>()) },
-            tag: <IndexPtr as ArenaAllocated>::tag(),
-        };
-
-        (allocated_ptr, untyped_arena)
-    }
-}
-
 #[repr(C)]
 #[derive(Debug)]
 pub struct TypedAllocSlab<T: ?Sized + ArenaAllocated> {
@@ -786,7 +475,8 @@ impl Drop for UntypedArenaSlab {
 #[derive(Debug)]
 pub struct Arena {
     base: Option<UntypedArenaSlab>,
-    pub f64_tbl: Arc<F64Table>,
+    pub f64_tbl: F64Table,
+    pub code_index_tbl: CodeIndexTable,
 }
 
 unsafe impl Send for Arena {}
@@ -799,6 +489,7 @@ impl Arena {
         Arena {
             base: None,
             f64_tbl: F64Table::new(),
+            code_index_tbl: CodeIndexTable::new(),
         }
     }
 }
@@ -874,11 +565,14 @@ unsafe fn drop_slab_in_place(value: NonNull<AllocSlab>, tag: ArenaHeaderTag) {
         ArenaHeaderTag::StandardErrorStream => {
             drop_typed_slab_in_place!(StandardErrorStream, value);
         }
-        ArenaHeaderTag::IndexPtrUndefined
+        ArenaHeaderTag::PipeReader => {
-        | ArenaHeaderTag::IndexPtrDynamicUndefined
+            drop_typed_slab_in_place!(PipeReader, value);
-        | ArenaHeaderTag::IndexPtrDynamicIndex
+        }
-        | ArenaHeaderTag::IndexPtrIndex => {
+        ArenaHeaderTag::PipeWriter => {
-            drop_typed_slab_in_place!(IndexPtr, value);
+            drop_typed_slab_in_place!(PipeWriter, value);
+        }
+        ArenaHeaderTag::ChildProcess => {
+            drop_typed_slab_in_place!(Child, value);
         }
         ArenaHeaderTag::NullStream => {
             unreachable!("NullStream is never arena allocated!");
@@ -904,35 +598,34 @@ const_assert!(mem::size_of::<OrderedFloat<f64>>() == 8);
 
 #[cfg(test)]
 mod tests {
-    use std::ops::Deref;
-
     use crate::arena::*;
     use crate::atom_table::*;
     use crate::machine::mock_wam::*;
-    use crate::machine::partial_string::*;
+    use crate::types::*;
 
     use crate::parser::dashu::{Integer, Rational};
     use ordered_float::OrderedFloat;
 
     #[test]
     fn float_ptr_cast() {
-        let wam = MockWAM::new();
+        let mut wam = MockWAM::new();
 
         let f = 0f64;
         let fp = float_alloc!(f, wam.machine_st.arena);
-        let mut cell = HeapCellValue::from(fp.clone());
+        let mut cell = HeapCellValue::from(fp);
 
-        assert_eq!(cell.get_tag(), HeapCellValueTag::F64);
+        assert_eq!(cell.get_tag(), HeapCellValueTag::F64Offset);
         assert!(!cell.get_mark_bit());
-        assert_eq!(fp.deref(), &OrderedFloat(f));
+        assert_eq!(wam.machine_st.arena.f64_tbl.get_entry(fp), OrderedFloat(f));
 
         cell.set_mark_bit(true);
 
         assert!(cell.get_mark_bit());
 
         read_heap_cell!(cell,
-            (HeapCellValueTag::F64, ptr) => {
+            (HeapCellValueTag::F64Offset, offset) => {
-                assert_eq!(OrderedFloat(*ptr), OrderedFloat(f))
+                let fp = wam.machine_st.arena.f64_tbl.get_entry(offset);
+                assert_eq!(fp, OrderedFloat(0f64))
             }
             _ => { unreachable!() }
         );
@@ -943,12 +636,12 @@ mod tests {
         let mut wam = MockWAM::new();
         #[cfg(target_pointer_width = "32")]
         let const_value = HeapCellValue::from(ConsPtr::build_with(
-            0x0000_0431 as *const _,
+            std::ptr::without_provenance(0x0000_0431),
             ConsPtrMaskTag::Cons,
         ));
         #[cfg(target_pointer_width = "64")]
         let const_value = HeapCellValue::from(ConsPtr::build_with(
-            0x0000_5555_ff00_0431 as *const _,
+            std::ptr::without_provenance(0x0000_5555_ff00_0431),
             ConsPtrMaskTag::Cons,
         ));
 
@@ -992,7 +685,7 @@ mod tests {
 
         assert!(!big_int_ptr.as_ptr().is_null());
 
-        let cell = HeapCellValue::from(Literal::Integer(big_int_ptr));
+        let cell = HeapCellValue::from(big_int_ptr);
         assert_eq!(cell.get_tag(), HeapCellValueTag::Cons);
 
         let untyped_arena_ptr = match cell.to_untyped_arena_ptr() {
@@ -1098,31 +791,6 @@ mod tests {
             _ => { unreachable!() }
         );
 
-        // complete string
-
-        let pstr_var_cell =
-            put_partial_string(&mut wam.machine_st.heap, "ronan", &wam.machine_st.atom_tbl);
-        let pstr_cell = wam.machine_st.heap[pstr_var_cell.get_value() as usize];
-
-        assert_eq!(pstr_cell.get_tag(), HeapCellValueTag::PStr);
-
-        match pstr_cell.to_pstr() {
-            Some(pstr) => {
-                assert_eq!(&*pstr.as_str_from(0), "ronan");
-            }
-            None => {
-                unreachable!();
-            }
-        }
-
-        read_heap_cell!(pstr_cell,
-            (HeapCellValueTag::PStr, pstr_atom) => {
-                let pstr = PartialString::from(pstr_atom);
-                assert_eq!(&*pstr.as_str_from(0), "ronan");
-            }
-            _ => { unreachable!() }
-        );
-
         // fixnum
 
         let fixnum_cell = fixnum_as_cell!(Fixnum::build_with(3));
@@ -1141,7 +809,9 @@ mod tests {
             _ => { unreachable!() }
         );
 
-        let fixnum_b_cell = fixnum_as_cell!(Fixnum::build_with(1 << 54));
+        let fixnum_b_cell = fixnum_as_cell!(
+            Fixnum::build_with_checked(1i64 << 54).expect("1 << 54 fits in Fixnum")
+        );
 
         assert_eq!(fixnum_b_cell.get_tag(), HeapCellValueTag::Fixnum);
 
@@ -1150,41 +820,29 @@ mod tests {
             None => unreachable!(),
         }
 
-        if Fixnum::build_with_checked(1 << 56).is_ok() {
+        Fixnum::build_with_checked(1i64 << 56).expect_err("1 << 56 is too large for fixnum");
-            unreachable!()
-        }
 
-        if Fixnum::build_with_checked(i64::MAX).is_ok() {
+        Fixnum::build_with_checked(i64::MAX).expect_err("i64::MAX is too large for Fixnum");
-            unreachable!()
+        Fixnum::build_with_checked(i64::MIN).expect_err("i64::MIN is too small for Fixnum");
-        }
+        assert_eq!(
+            Fixnum::build_with_checked(-1i64)
+                .expect("-1 fits in fixnum")
+                .get_num(),
+            -1
+        );
 
-        if Fixnum::build_with_checked(i64::MIN).is_ok() {
+        Fixnum::build_with_checked((1i64 << 55) - 1)
-            unreachable!()
+            .expect("(1 << 55) - 1 is the largest value that fits in Fixnum");
-        }
 
-        match Fixnum::build_with_checked(-1) {
+        Fixnum::build_with_checked(-(1i64 << 55))
-            Ok(n) => assert_eq!(n.get_num(), -1),
+            .expect("-(1 << 55) is the smallest value that fits in fixnum");
-            _ => unreachable!(),
+        Fixnum::build_with_checked(-(1i64 << 55) - 1)
-        }
+            .expect_err("-(1<<55) - 1 is too small for Fixnum");
 
-        match Fixnum::build_with_checked((1 << 55) - 1) {
+        assert_eq!(
-            Ok(n) => assert_eq!(n.get_num(), (1 << 55) - 1),
+            -Fixnum::build_with_checked(-1i64).expect("-1 fits in Fixnum"),
-            _ => unreachable!(),
+            Fixnum::build_with(1)
-        }
+        );
-
-        match Fixnum::build_with_checked(-(1 << 55)) {
-            Ok(n) => assert_eq!(n.get_num(), -(1 << 55)),
-            _ => unreachable!(),
-        }
-
-        if Fixnum::build_with_checked(-(1 << 55) - 1).is_ok() {
-            unreachable!()
-        }
-
-        match Fixnum::build_with_checked(-1) {
-            Ok(n) => assert_eq!(-n, Fixnum::build_with(1)),
-            _ => unreachable!(),
-        }
 
         // float
 
@@ -1192,7 +850,7 @@ mod tests {
         let float_ptr = float_alloc!(float, wam.machine_st.arena);
         let cell = HeapCellValue::from(float_ptr);
 
-        assert_eq!(cell.get_tag(), HeapCellValueTag::F64);
+        assert_eq!(cell.get_tag(), HeapCellValueTag::F64Offset);
 
         // char
 
@@ -1200,8 +858,8 @@ mod tests {
         let char_cell = char_as_cell!(c);
 
         read_heap_cell!(char_cell,
-            (HeapCellValueTag::Char, c) => {
+            (HeapCellValueTag::Atom, (c, _arity)) => {
-                assert_eq!(c, 'c');
+                assert_eq!(&*c.as_str(), "c");
             }
             _ => { unreachable!() }
         );
@@ -1210,8 +868,8 @@ mod tests {
         let cyrillic_char_cell = char_as_cell!(c);
 
         read_heap_cell!(cyrillic_char_cell,
-            (HeapCellValueTag::Char, c) => {
+            (HeapCellValueTag::Atom, (c, _arity)) => {
-                assert_eq!(c, 'Ћ');
+                assert_eq!(&*c.as_str(), "Ћ");
             }
             _ => { unreachable!() }
         );

src/arithmetic.rs

@@ -7,6 +7,7 @@ use crate::debray_allocator::*;
 use crate::forms::*;
 use crate::instructions::*;
 use crate::iterators::*;
+use crate::offset_table::*;
 use crate::targets::QueryInstruction;
 use crate::types::*;
 
@@ -88,7 +89,7 @@ impl<'a> ArithInstructionIterator<'a> {
 
 #[derive(Debug)]
 pub(crate) enum ArithTermRef<'a> {
-    Literal(&'a Literal),
+    Literal(Literal),
     Op(Atom, usize), // name, arity.
     Var(Level, &'a Cell<VarReg>, VarPtr),
 }
@@ -117,7 +118,7 @@ impl<'a> Iterator for ArithInstructionIterator<'a> {
                         self.push_subterm(lvl.child_level(), &subterms[child_num]);
                     }
                 }
-                TermIterState::Literal(_, _, c) => return Some(Ok(ArithTermRef::Literal(c))),
+                TermIterState::Literal(_, _, c) => return Some(Ok(ArithTermRef::Literal(*c))),
                 TermIterState::Var(lvl, cell, var_ptr) => {
                     return Some(Ok(ArithTermRef::Var(lvl, cell, var_ptr)));
                 }
@@ -137,6 +138,7 @@ impl<'a> Iterator for ArithInstructionIterator<'a> {
 #[derive(Debug)]
 pub(crate) struct ArithmeticEvaluator<'a> {
     marker: &'a mut DebrayAllocator,
+    f64_tbl: &'a F64Table,
     interm: Vec<ArithmeticTerm>,
     interm_c: usize,
 }
@@ -155,11 +157,18 @@ impl<'a> ArithmeticTermIter<'a> for &'a Term {
     }
 }
 
-fn push_literal(interm: &mut Vec<ArithmeticTerm>, c: &Literal) -> Result<(), ArithmeticError> {
+fn push_literal(
+    f64_tbl: &F64Table,
+    interm: &mut Vec<ArithmeticTerm>,
+    c: &Literal,
+) -> Result<(), ArithmeticError> {
     match c {
         Literal::Fixnum(n) => interm.push(ArithmeticTerm::Number(Number::Fixnum(*n))),
         Literal::Integer(n) => interm.push(ArithmeticTerm::Number(Number::Integer(*n))),
-        Literal::Float(n) => interm.push(ArithmeticTerm::Number(Number::Float(*n.as_ptr()))),
+        &Literal::F64Offset(offset) => {
+            let n = f64_tbl.get_entry(offset);
+            interm.push(ArithmeticTerm::Number(Number::Float(n)));
+        }
         Literal::Rational(n) => interm.push(ArithmeticTerm::Number(Number::Rational(*n))),
         Literal::Atom(name) if name == &atom!("e") => interm.push(ArithmeticTerm::Number(
             Number::Float(OrderedFloat(std::f64::consts::E)),
@@ -177,9 +186,14 @@ fn push_literal(interm: &mut Vec<ArithmeticTerm>, c: &Literal) -> Result<(), Ari
 }
 
 impl<'a> ArithmeticEvaluator<'a> {
-    pub(crate) fn new(marker: &'a mut DebrayAllocator, target_int: usize) -> Self {
+    pub(crate) fn new(
+        marker: &'a mut DebrayAllocator,
+        f64_tbl: &'a F64Table,
+        target_int: usize,
+    ) -> Self {
         ArithmeticEvaluator {
             marker,
+            f64_tbl,
             interm: Vec::new(),
             interm_c: target_int,
         }
@@ -317,7 +331,7 @@ impl<'a> ArithmeticEvaluator<'a> {
 
         for term_ref in src.iter()? {
             match term_ref? {
-                ArithTermRef::Literal(c) => push_literal(&mut self.interm, c)?,
+                ArithTermRef::Literal(c) => push_literal(self.f64_tbl, &mut self.interm, &c)?,
                 ArithTermRef::Var(lvl, cell, name) => {
                     let var_num = name.to_var_num().unwrap();
 
@@ -357,9 +371,8 @@ impl<'a> ArithmeticEvaluator<'a> {
 pub(crate) fn rnd_i(n: &'_ Number, arena: &mut Arena) -> Result<Number, EvalError> {
     match n {
         &Number::Integer(i) => {
-            let result = (&*i).try_into();
+            if let Ok(value) = Fixnum::build_with_checked(&*i) {
-            if let Ok(value) = result {
+                Ok(Number::Fixnum(value))
-                Ok(fixnum!(Number, value, arena))
             } else {
                 Ok(*n)
             }
@@ -368,11 +381,14 @@ pub(crate) fn rnd_i(n: &'_ Number, arena: &mut Arena) -> Result<Number, EvalErro
         &Number::Float(f) => {
             let f = f.floor();
 
-            const I64_MIN_TO_F: OrderedFloat<f64> = OrderedFloat(i64::MIN as f64);
+            const FIXNUM_MIN_TO_F: OrderedFloat<f64> = OrderedFloat(Fixnum::MIN as f64);
-            const I64_MAX_TO_F: OrderedFloat<f64> = OrderedFloat(i64::MAX as f64);
+            const FIXNUM_MAX_TO_F: OrderedFloat<f64> = OrderedFloat(Fixnum::MAX as f64);
 
-            if I64_MIN_TO_F <= f && f <= I64_MAX_TO_F {
+            if (FIXNUM_MIN_TO_F..=FIXNUM_MAX_TO_F).contains(&f) {
-                Ok(fixnum!(Number, f.into_inner() as i64, arena))
+                Ok(Number::Fixnum(
+                    // Safety: We checked that the value is in range
+                    unsafe { Fixnum::build_with_unchecked(f.into_inner() as i64) },
+                ))
             } else {
                 Ok(Number::Integer(arena_alloc!(
                     Integer::try_from(classify_float(f.0)?).unwrap_or_else(|_| {
@@ -385,8 +401,8 @@ pub(crate) fn rnd_i(n: &'_ Number, arena: &mut Arena) -> Result<Number, EvalErro
         Number::Rational(ref r) => {
             let floor = r.floor();
 
-            if let Ok(value) = (&floor).try_into() {
+            if let Ok(value) = Fixnum::build_with_checked(&floor) {
-                Ok(fixnum!(Number, value, arena))
+                Ok(Number::Fixnum(value))
             } else {
                 Ok(Number::Integer(arena_alloc!(floor, arena)))
             }
@@ -649,11 +665,11 @@ impl Ord for Number {
     }
 }
 
-impl TryFrom<HeapCellValue> for Number {
+impl TryFrom<(HeapCellValue, &'_ F64Table)> for Number {
     type Error = ();
 
     #[inline]
-    fn try_from(value: HeapCellValue) -> Result<Number, Self::Error> {
+    fn try_from((value, f64_tbl): (HeapCellValue, &F64Table)) -> Result<Number, Self::Error> {
         read_heap_cell!(value,
            (HeapCellValueTag::Cons, c) => {
                match_untyped_arena_ptr!(c,
@@ -668,8 +684,9 @@ impl TryFrom<HeapCellValue> for Number {
                   }
                )
            }
-           (HeapCellValueTag::F64, n) => {
+           (HeapCellValueTag::F64Offset, offset) => {
-               Ok(Number::Float(*n))
+               let n = f64_tbl.get_entry(offset);
+               Ok(Number::Float(n))
            }
            (HeapCellValueTag::Fixnum | HeapCellValueTag::CutPoint, n) => {
                Ok(Number::Fixnum(n))

src/atom_table.rs

@@ -23,15 +23,124 @@ use indexmap::IndexSet;
 
 use scryer_modular_bitfield::prelude::*;
 
+#[bitfield]
+#[repr(u64)]
+#[derive(Copy, Clone, Debug)]
+pub struct AtomCell {
+    name: B48,
+    arity: B8,
+    #[allow(unused)]
+    f: bool,
+    #[allow(unused)]
+    m: bool,
+    #[allow(unused)]
+    is_inlined: bool,
+    #[allow(unused)]
+    tag: B5,
+}
+
+const INLINED_ATOM_MAX_LEN: usize = 6;
+
+const_assert!(INLINED_ATOM_MAX_LEN < mem::size_of::<AtomCell>());
+const_assert!(mem::size_of::<AtomCell>() == 8);
+
+const_assert!(INLINED_ATOM_MAX_LEN < mem::size_of::<Atom>());
+const_assert!(mem::size_of::<Atom>() == 8);
+
+impl AtomCell {
+    #[inline]
+    fn new_static(index: u64) -> Self {
+        // upper 23 bits of index must be 0
+        debug_assert_eq!(index & !((1 << 49) - 1), 0);
+        AtomCell::new()
+            .with_name(index)
+            .with_arity(0u8)
+            .with_m(false)
+            .with_f(false)
+            .with_is_inlined(false)
+            .with_tag(HeapCellValueTag::Atom as u8)
+    }
+
+    #[inline]
+    fn new_inlined(string: &str, arity: u8) -> Self {
+        debug_assert!(string.len() <= INLINED_ATOM_MAX_LEN);
+
+        let mut string_buf: [u8; 8] = [0u8; 8];
+        string_buf[..string.len()].copy_from_slice(string.as_bytes());
+        let encoding = u64::from_le_bytes(string_buf);
+
+        AtomCell::new()
+            .with_name(encoding)
+            .with_arity(arity)
+            .with_m(false)
+            .with_f(false)
+            .with_is_inlined(true)
+            .with_tag(HeapCellValueTag::Atom as u8)
+    }
+
+    #[inline]
+    pub fn new_char_inlined(c: char) -> Self {
+        if c == '\u{0}' {
+            return Self::new_static(NULL_ATOM.flat_index());
+        }
+
+        let mut char_buf = [0u8; 8];
+        c.encode_utf8(&mut char_buf);
+
+        let encoding = u64::from_le_bytes(char_buf);
+
+        AtomCell::new()
+            .with_name(encoding)
+            .with_arity(0u8)
+            .with_m(false)
+            .with_f(false)
+            .with_is_inlined(true)
+            .with_tag(HeapCellValueTag::Atom as u8)
+    }
+
+    #[inline]
+    pub fn build_with(atom_index: u64, arity: u8) -> Self {
+        debug_assert!((arity as usize) <= MAX_ARITY);
+
+        AtomCell::new()
+            .with_name(atom_index >> 1)
+            .with_arity(arity)
+            .with_f(false)
+            .with_m(false)
+            .with_is_inlined(atom_index & 1 == 1)
+            .with_tag(HeapCellValueTag::Atom as u8)
+    }
+
+    #[inline]
+    pub fn get_name(self) -> Atom {
+        Atom {
+            index: (self.name() << 1) | self.is_inlined() as u64,
+        }
+    }
+
+    #[inline]
+    pub fn get_arity(self) -> usize {
+        self.arity() as usize
+    }
+
+    #[inline]
+    pub fn get_name_and_arity(self) -> (Atom, usize) {
+        (self.get_name(), self.get_arity())
+    }
+}
+
 #[derive(Copy, Clone, Debug, PartialEq, Eq)]
 pub struct Atom {
     pub index: u64,
 }
 
-const_assert!(mem::size_of::<Atom>() == 8);
-
 include!(concat!(env!("OUT_DIR"), "/static_atoms.rs"));
 
+// populate these in STRINGS so they can be used from build_functor
+const _: Atom = atom!(".");
+const _: Atom = atom!("[]");
+const NULL_ATOM: Atom = atom!("\0");
+
 impl<'a> From<&'a Atom> for Atom {
     #[inline]
     fn from(atom: &'a Atom) -> Self {
@@ -39,17 +148,6 @@ impl<'a> From<&'a Atom> for Atom {
     }
 }
 
-impl From<bool> for Atom {
-    #[inline]
-    fn from(value: bool) -> Self {
-        if value {
-            atom!("true")
-        } else {
-            atom!("false")
-        }
-    }
-}
-
 impl indexmap::Equivalent<Atom> for str {
     fn equivalent(&self, key: &Atom) -> bool {
         &*key.as_str() == self
@@ -120,25 +218,23 @@ impl Hash for Atom {
     #[inline]
     fn hash<H: Hasher>(&self, hasher: &mut H) {
         self.as_str().hash(hasher)
-        // hasher.write_usize(self.index)
     }
 }
 
 pub enum AtomString<'a> {
     Static(&'a str),
+    Inlined([u8; 8]),
     Dynamic(AtomTableRef<str>),
 }
 
-impl AtomString<'_> {
+#[inline(always)]
-    pub fn map<F>(self, f: F) -> Self
+fn inlined_to_str(bytes: &[u8; 8]) -> &str {
-    where
+    let slice_len = bytes
-        for<'a> F: FnOnce(&'a str) -> &'a str,
+        .iter()
-    {
+        .position(|&b| b == 0u8)
-        match self {
+        .unwrap_or(INLINED_ATOM_MAX_LEN);
-            Self::Static(reference) => Self::Static(f(reference)),
+
-            Self::Dynamic(guard) => Self::Dynamic(AtomTableRef::map(guard, f)),
+    unsafe { str::from_utf8_unchecked(&bytes[..slice_len]) }
-        }
-    }
 }
 
 impl std::fmt::Debug for AtomString<'_> {
@@ -158,6 +254,7 @@ impl std::ops::Deref for AtomString<'_> {
     fn deref(&self) -> &Self::Target {
         match self {
             Self::Static(reference) => reference,
+            Self::Inlined(inlined) => inlined_to_str(inlined),
             Self::Dynamic(guard) => guard.deref(),
         }
     }
@@ -175,13 +272,32 @@ impl rustyline::completion::Candidate for AtomString<'_> {
 }
 
 impl Atom {
-    #[inline(always)]
+    #[inline]
-    pub fn is_static(self) -> bool {
+    fn new_inlined(string: &str) -> Self {
-        (self.index as usize) < STRINGS.len() << 3
+        AtomCell::new_inlined(string, 0).get_name()
     }
 
     #[inline(always)]
-    pub fn as_ptr(self) -> Option<AtomTableRef<AtomData>> {
+    fn is_static(self) -> bool {
+        if self.is_inlined() {
+            true
+        } else {
+            (self.flat_index() as usize) < STRINGS.len()
+        }
+    }
+
+    #[inline]
+    pub(crate) fn flat_index(self) -> u64 {
+        self.index >> 1
+    }
+
+    #[inline(always)]
+    pub(crate) fn is_inlined(self) -> bool {
+        self.index & 1 == 1
+    }
+
+    #[inline(always)]
+    fn as_ptr(self) -> Option<AtomTableRef<AtomData>> {
         if self.is_static() {
             None
         } else {
@@ -192,7 +308,7 @@ impl Atom {
                 let ptr = buf
                     .block
                     .base
-                    .add((self.index as usize) - (STRINGS.len() << 3));
+                    .add(self.flat_index() as usize - STRINGS.len());
                 // TODO use std::ptr::from_raw_parts instead when feature ptr_metadata is stable rust-lang/rust#81513
                 let atom_data = &*(std::ptr::slice_from_raw_parts(ptr, 0) as *const AtomData);
                 let len = atom_data.header.len();
@@ -208,8 +324,11 @@ impl Atom {
 
     #[inline(always)]
     pub fn len(self) -> usize {
-        if self.is_static() {
+        if let Some(s) = self.inlined_str() {
-            STRINGS[(self.index >> 3) as usize].len()
+            s.len()
+        } else if self.is_static() {
+            let index = self.flat_index();
+            STRINGS[index as usize].len()
         } else {
             let len: u64 = self.as_ptr().unwrap().header.len();
             len as usize
@@ -220,11 +339,6 @@ impl Atom {
         self.len() == 0
     }
 
-    #[inline(always)]
-    pub fn flat_index(self) -> u64 {
-        self.index >> 3
-    }
-
     pub fn as_char(self) -> Option<char> {
         let s = self.as_str();
         let mut it = s.chars();
@@ -239,14 +353,26 @@ impl Atom {
         }
     }
 
+    #[inline]
+    fn inlined_str<'a>(&self) -> Option<AtomString<'a>> {
+        if self.is_inlined() {
+            Some(AtomString::Inlined(self.flat_index().to_le_bytes()))
+        } else {
+            None
+        }
+    }
+
     #[inline]
     pub fn as_str(&self) -> AtomString<'static> {
-        if self.is_static() {
+        if let Some(s) = self.inlined_str() {
-            AtomString::Static(STRINGS[(self.index >> 3) as usize])
+            s
+        } else if self.is_static() {
+            let index = self.flat_index() as usize;
+            AtomString::Static(STRINGS[index])
         } else if let Some(ptr) = self.as_ptr() {
             AtomString::Dynamic(AtomTableRef::map(ptr, |ptr| &ptr.data))
         } else {
-            AtomString::Static(STRINGS[(self.index >> 3) as usize])
+            AtomString::Static(STRINGS[(self.index >> 1) as usize])
         }
     }
 
@@ -342,6 +468,10 @@ impl AtomTable {
     }
 
     pub fn build_with(atom_table: &AtomTable, string: &str) -> Atom {
+        if !string.is_empty() && string.len() <= INLINED_ATOM_MAX_LEN && !string.contains('\u{0}') {
+            return Atom::new_inlined(string);
+        }
+
         loop {
             let mut block_epoch = atom_table.inner.read();
             let mut table_epoch = block_epoch.table.read();
@@ -386,13 +516,18 @@ impl AtomTable {
                     }
                 };
 
-                let ptr_base = block_epoch.block.base as usize;
+                let ptr_base = block_epoch.block.base.addr();
 
                 write_to_ptr(string, len_ptr);
 
-                let atom = Atom {
+                let atom = AtomCell::new()
-                    index: ((STRINGS.len() << 3) + len_ptr as usize - ptr_base) as u64,
+                    .with_name((STRINGS.len() + len_ptr.addr() - ptr_base) as u64)
-                };
+                    .with_arity(0)
+                    .with_f(false)
+                    .with_m(false)
+                    .with_is_inlined(false)
+                    .with_tag(HeapCellValueTag::Atom as u8)
+                    .get_name();
 
                 let mut table = table_epoch.clone();
                 table.insert(atom);
@@ -409,57 +544,3 @@ impl AtomTable {
 
 unsafe impl Send for AtomTable {}
 unsafe impl Sync for AtomTable {}
-
-#[bitfield]
-#[repr(u64)]
-#[derive(Copy, Clone, Debug)]
-pub struct AtomCell {
-    name: B46,
-    arity: B10,
-    #[allow(unused)]
-    f: bool,
-    #[allow(unused)]
-    m: bool,
-    #[allow(unused)]
-    tag: B6,
-}
-
-impl AtomCell {
-    #[inline]
-    pub fn build_with(name: u64, arity: u16, tag: HeapCellValueTag) -> Self {
-        if arity > 0 {
-            debug_assert!(arity as usize <= MAX_ARITY);
-
-            AtomCell::new()
-                .with_name(name)
-                .with_arity(arity)
-                .with_f(false)
-                .with_tag(tag as u8)
-        } else {
-            AtomCell::new()
-                .with_name(name)
-                .with_f(false)
-                .with_tag(tag as u8)
-        }
-    }
-
-    #[inline]
-    pub fn get_index(self) -> usize {
-        self.name() as usize
-    }
-
-    #[inline]
-    pub fn get_name(self) -> Atom {
-        Atom::from((self.get_index() as u64) << 3)
-    }
-
-    #[inline]
-    pub fn get_arity(self) -> usize {
-        self.arity() as usize
-    }
-
-    #[inline]
-    pub fn get_name_and_arity(self) -> (Atom, usize) {
-        (Atom::from((self.get_index() as u64) << 3), self.get_arity())
-    }
-}

src/codegen.rs

@@ -6,6 +6,7 @@ use crate::forms::*;
 use crate::indexing::*;
 use crate::instructions::*;
 use crate::iterators::*;
+use crate::offset_table::F64Table;
 use crate::parser::ast::*;
 use crate::targets::*;
 use crate::types::*;
@@ -269,10 +270,10 @@ impl CodeGenSettings {
 }
 
 #[derive(Debug)]
-pub(crate) struct CodeGenerator<'a> {
+pub(crate) struct CodeGenerator<'f64_tbl> {
-    pub(crate) atom_tbl: &'a AtomTable,
     marker: DebrayAllocator,
     settings: CodeGenSettings,
+    f64_tbl: &'f64_tbl F64Table,
     pub(crate) skeleton: PredicateSkeleton,
 }
 
@@ -319,33 +320,12 @@ impl DebrayAllocator {
     }
 }
 
-// if the final argument of the structure is a Literal::Index,
-// decrement the arity of the PutStructure instruction by 1.
-fn trim_structure_by_last_arg(instr: &mut Instruction, last_arg: &Term) {
-    match instr {
-        Instruction::PutStructure(_, ref mut arity, _)
-        | Instruction::GetStructure(.., ref mut arity, _) => {
-            if let Term::Literal(_, Literal::CodeIndex(_)) = last_arg {
-                // it is acceptable if arity == 0 is the result of
-                // this decrement. call/N will have to read the index
-                // constant for '$call_inline' to succeed. to find it,
-                // it must know the heap location of the index.
-                // self.store must stop before reading the atom into a
-                // register.
-
-                *arity -= 1;
-            }
-        }
-        _ => {}
-    }
-}
-
 trait AddToFreeList<'a, Target: CompilationTarget<'a>> {
     fn add_term_to_free_list(&mut self, r: RegType);
     fn add_subterm_to_free_list(&mut self, term: &Term);
 }
 
-impl<'a, 'b> AddToFreeList<'a, FactInstruction> for CodeGenerator<'b> {
+impl<'a> AddToFreeList<'a, FactInstruction> for CodeGenerator<'_> {
     fn add_term_to_free_list(&mut self, r: RegType) {
         self.marker.add_reg_to_free_list(r);
     }
@@ -353,7 +333,7 @@ impl<'a, 'b> AddToFreeList<'a, FactInstruction> for CodeGenerator<'b> {
     fn add_subterm_to_free_list(&mut self, _term: &Term) {}
 }
 
-impl<'a, 'b> AddToFreeList<'a, QueryInstruction> for CodeGenerator<'b> {
+impl<'a> AddToFreeList<'a, QueryInstruction> for CodeGenerator<'_> {
     #[inline(always)]
     fn add_term_to_free_list(&mut self, _r: RegType) {}
 
@@ -375,12 +355,12 @@ fn structure_cell(term: &Term) -> Option<&Cell<RegType>> {
     }
 }
 
-impl<'b> CodeGenerator<'b> {
+impl<'f64_tbl> CodeGenerator<'f64_tbl> {
-    pub(crate) fn new(atom_tbl: &'b AtomTable, settings: CodeGenSettings) -> Self {
+    pub(crate) fn new(f64_tbl: &'f64_tbl F64Table, settings: CodeGenSettings) -> Self {
         CodeGenerator {
-            atom_tbl,
             marker: DebrayAllocator::new(),
             settings,
+            f64_tbl,
             skeleton: PredicateSkeleton::new(),
         }
     }
@@ -446,99 +426,99 @@ impl<'b> CodeGenerator<'b> {
         };
     }
 
-    fn compile_target<'a, Target, Iter>(&mut self, iter: Iter, term_loc: GenContext) -> CodeDeque
+    fn compile_target<'a, Target, Iter>(&mut self, iter: Iter, context: GenContext) -> CodeDeque
     where
         Target: crate::targets::CompilationTarget<'a>,
         Iter: Iterator<Item = TermRef<'a>>,
-        CodeGenerator<'b>: AddToFreeList<'a, Target>,
+        CodeGenerator<'f64_tbl>: AddToFreeList<'a, Target>,
     {
         let mut target = CodeDeque::new();
 
         for term in iter {
             match term {
                 TermRef::AnonVar(lvl @ Level::Shallow) => {
-                    if let GenContext::Head = term_loc {
+                    if let GenContext::Head = context {
                         self.marker.advance_arg();
                     } else {
                         self.marker
-                            .mark_anon_var::<Target>(lvl, term_loc, &mut target);
+                            .mark_anon_var::<Target>(lvl, context, &mut target);
                     }
                 }
                 TermRef::Clause(lvl, cell, name, terms) => {
-                    self.marker
+                    let terms_range =
-                        .mark_non_var::<Target>(lvl, term_loc, cell, &mut target);
+                        if let Some(subterm @ Term::Literal(_, Literal::CodeIndexOffset(_))) =
-                    target.push_back(Target::to_structure(lvl, name, terms.len(), cell.get()));
+                            terms.last()
+                        {
+                            self.subterm_to_instr::<Target>(subterm, context, &mut target);
+                            0..terms.len() - 1
+                        } else {
+                            0..terms.len()
+                        };
 
-                    <CodeGenerator<'b> as AddToFreeList<'a, Target>>::add_term_to_free_list(
+                    self.marker
+                        .mark_non_var::<Target>(lvl, context, cell, &mut target);
+                    target.push_back(Target::to_structure(lvl, name, terms_range.end, cell.get()));
+
+                    <CodeGenerator as AddToFreeList<'a, Target>>::add_term_to_free_list(
                         self,
                         cell.get(),
                     );
 
-                    if let Some(instr) = target.back_mut() {
+                    for subterm in &terms[terms_range.clone()] {
-                        if let Some(term) = terms.last() {
+                        self.subterm_to_instr::<Target>(subterm, context, &mut target);
-                            trim_structure_by_last_arg(instr, term);
-                        }
                     }
 
-                    for subterm in terms {
+                    for subterm in &terms[terms_range] {
-                        self.subterm_to_instr::<Target>(subterm, term_loc, &mut target);
+                        <CodeGenerator as AddToFreeList<'a, Target>>::add_subterm_to_free_list(
-                    }
-
-                    for subterm in terms {
-                        <CodeGenerator<'b> as AddToFreeList<'a, Target>>::add_subterm_to_free_list(
                             self, subterm,
                         );
                     }
                 }
                 TermRef::Cons(lvl, cell, head, tail) => {
                     self.marker
-                        .mark_non_var::<Target>(lvl, term_loc, cell, &mut target);
+                        .mark_non_var::<Target>(lvl, context, cell, &mut target);
                     target.push_back(Target::to_list(lvl, cell.get()));
 
-                    <CodeGenerator<'b> as AddToFreeList<'a, Target>>::add_term_to_free_list(
+                    <CodeGenerator as AddToFreeList<'a, Target>>::add_term_to_free_list(
                         self,
                         cell.get(),
                     );
 
-                    self.subterm_to_instr::<Target>(head, term_loc, &mut target);
+                    self.subterm_to_instr::<Target>(head, context, &mut target);
-                    self.subterm_to_instr::<Target>(tail, term_loc, &mut target);
+                    self.subterm_to_instr::<Target>(tail, context, &mut target);
 
-                    <CodeGenerator<'b> as AddToFreeList<'a, Target>>::add_subterm_to_free_list(
+                    <CodeGenerator as AddToFreeList<'a, Target>>::add_subterm_to_free_list(
                         self, head,
                     );
-                    <CodeGenerator<'b> as AddToFreeList<'a, Target>>::add_subterm_to_free_list(
+                    <CodeGenerator as AddToFreeList<'a, Target>>::add_subterm_to_free_list(
                         self, tail,
                     );
                 }
-                TermRef::Literal(lvl @ Level::Shallow, cell, Literal::String(ref string)) => {
-                    self.marker
-                        .mark_non_var::<Target>(lvl, term_loc, cell, &mut target);
-                    target.push_back(Target::to_pstr(lvl, *string, cell.get(), false));
-                }
                 TermRef::Literal(lvl @ Level::Shallow, cell, constant) => {
                     self.marker
-                        .mark_non_var::<Target>(lvl, term_loc, cell, &mut target);
+                        .mark_non_var::<Target>(lvl, context, cell, &mut target);
                     target.push_back(Target::to_constant(lvl, *constant, cell.get()));
                 }
                 TermRef::PartialString(lvl, cell, string, tail) => {
                     self.marker
-                        .mark_non_var::<Target>(lvl, term_loc, cell, &mut target);
+                        .mark_non_var::<Target>(lvl, context, cell, &mut target);
-                    let atom = AtomTable::build_with(self.atom_tbl, string);
 
-                    target.push_back(Target::to_pstr(lvl, atom, cell.get(), true));
+                    target.push_back(Target::to_pstr(lvl, string.clone(), cell.get()));
-                    self.subterm_to_instr::<Target>(tail, term_loc, &mut target);
+                    self.subterm_to_instr::<Target>(tail, context, &mut target);
                 }
-                TermRef::CompleteString(lvl, cell, atom) => {
+                TermRef::CompleteString(lvl, cell, string) => {
                     self.marker
-                        .mark_non_var::<Target>(lvl, term_loc, cell, &mut target);
+                        .mark_non_var::<Target>(lvl, context, cell, &mut target);
-                    target.push_back(Target::to_pstr(lvl, atom, cell.get(), false));
+
+                    target.push_back(Target::to_pstr(lvl, string.clone(), cell.get()));
+                    target.push_back(Target::constant_subterm(Literal::Atom(atom!("[]"))));
                 }
                 TermRef::Var(lvl @ Level::Shallow, cell, var) => {
                     self.marker.mark_var::<Target>(
                         var.to_var_num().unwrap(),
                         lvl,
                         cell,
-                        term_loc,
+                        context,
                         &mut target,
                     );
                 }
@@ -600,9 +580,7 @@ impl<'b> CodeGenerator<'b> {
                 compare_number_instr!(cmp, at_1, at_2)
             }
             InlinedClauseType::IsAtom(..) => match &terms[0] {
-                Term::Literal(_, Literal::Char(_))
+                Term::Literal(_, Literal::Atom(..)) => {
-                | Term::Literal(_, Literal::Atom(atom!("[]")))
-                | Term::Literal(_, Literal::Atom(..)) => {
                     instr!("$succeed")
                 }
                 Term::Var(ref vr, ref name) => {
@@ -630,9 +608,6 @@ impl<'b> CodeGenerator<'b> {
                 | Term::CompleteString(..) => {
                     instr!("$fail")
                 }
-                Term::Literal(_, Literal::String(_)) => {
-                    instr!("$fail")
-                }
                 Term::Literal(..) => {
                     instr!("$succeed")
                 }
@@ -654,8 +629,7 @@ impl<'b> CodeGenerator<'b> {
                 Term::Clause(..)
                 | Term::Cons(..)
                 | Term::PartialString(..)
-                | Term::CompleteString(..)
+                | Term::CompleteString(..) => {
-                | Term::Literal(_, Literal::String(..)) => {
                     instr!("$succeed")
                 }
                 Term::Var(ref vr, ref name) => {
@@ -695,7 +669,7 @@ impl<'b> CodeGenerator<'b> {
                 }
             },
             InlinedClauseType::IsFloat(..) => match terms[0] {
-                Term::Literal(_, Literal::Float(_)) => {
+                Term::Literal(_, Literal::F64Offset(_)) => {
                     instr!("$succeed")
                 }
                 Term::Var(ref vr, ref name) => {
@@ -716,7 +690,7 @@ impl<'b> CodeGenerator<'b> {
                 }
             },
             InlinedClauseType::IsNumber(..) => match terms[0] {
-                Term::Literal(_, Literal::Float(_))
+                Term::Literal(_, Literal::F64Offset(_))
                 | Term::Literal(_, Literal::Rational(_))
                 | Term::Literal(_, Literal::Integer(_))
                 | Term::Literal(_, Literal::Fixnum(_)) => {
@@ -810,7 +784,6 @@ impl<'b> CodeGenerator<'b> {
 
         // inlined predicates are never counted, so this overrides nothing.
         self.add_call(code, call_instr, CallPolicy::Counted);
-
         Ok(())
     }
 
@@ -821,7 +794,7 @@ impl<'b> CodeGenerator<'b> {
         term_loc: GenContext,
         arg: usize,
     ) -> Result<ArithCont, ArithmeticError> {
-        let mut evaluator = ArithmeticEvaluator::new(&mut self.marker, target_int);
+        let mut evaluator = ArithmeticEvaluator::new(&mut self.marker, self.f64_tbl, target_int);
         evaluator.compile_is(term, term_loc, arg)
     }
 
@@ -891,7 +864,7 @@ impl<'b> CodeGenerator<'b> {
             Term::Literal(
                 _,
                 c @ Literal::Integer(_)
-                | c @ Literal::Float(_)
+                | c @ Literal::F64Offset(_)
                 | c @ Literal::Rational(_)
                 | c @ Literal::Fixnum(_),
             ) => {
@@ -909,7 +882,6 @@ impl<'b> CodeGenerator<'b> {
 
         let at = at.unwrap_or(interm!(1));
         self.add_call(code, instr!("is", temp_v!(1), at), call_policy);
-
         Ok(())
     }
 
@@ -924,9 +896,9 @@ impl<'b> CodeGenerator<'b> {
 
         while let Some(clause_item) = clause_iter.next() {
             match clause_item {
-                ClauseItem::Chunk(chunk) => {
+                ClauseItem::Chunk { terms } => {
-                    for (idx, term) in chunk.iter().enumerate() {
+                    for (idx, term) in terms.iter().enumerate() {
-                        let term_loc = if idx + 1 < chunk.len() {
+                        let term_loc = if idx + 1 < terms.len() {
                             GenContext::Mid(chunk_num)
                         } else {
                             self.marker.in_tail_position = clause_iter.in_tail_position();
@@ -1147,27 +1119,24 @@ impl<'b> CodeGenerator<'b> {
         'outer: for (right, clause) in clauses.iter().enumerate() {
             if let Some(args) = clause.args() {
                 for (instantiated_arg_index, arg) in args.iter().enumerate() {
-                    match arg {
+                    if !matches!(arg, Term::Var(..) | Term::AnonVar) {
-                        Term::Var(..) | Term::AnonVar => {}
+                        if optimal_index != instantiated_arg_index {
-                        _ => {
+                            if left >= right {
-                            if optimal_index != instantiated_arg_index {
-                                if left >= right {
-                                    optimal_index = instantiated_arg_index;
-                                    continue 'outer;
-                                }
-
-                                subseqs.push(ClauseSpan {
-                                    left,
-                                    right,
-                                    instantiated_arg_index: optimal_index,
-                                });
-
                                 optimal_index = instantiated_arg_index;
-                                left = right;
+                                continue 'outer;
                             }
 
-                            continue 'outer;
+                            subseqs.push(ClauseSpan {
+                                left,
+                                right,
+                                instantiated_arg_index: optimal_index,
+                            });
+
+                            optimal_index = instantiated_arg_index;
+                            left = right;
                         }
+
+                        continue 'outer;
                     }
                 }
             }
@@ -1260,7 +1229,7 @@ impl<'b> CodeGenerator<'b> {
                 let index = code.len();
 
                 if clauses_len > 1 || self.settings.is_extensible {
-                    code_offsets.index_term(arg, index, &mut clause_index_info, self.atom_tbl);
+                    code_offsets.index_term(arg, index, &mut clause_index_info);
                 }
             }
 

src/debray_allocator.rs

@@ -1,6 +1,6 @@
 use crate::allocator::*;
 use crate::codegen::SubsumedBranchHits;
-use crate::forms::Level;
+use crate::forms::{GenContext, Level};
 use crate::instructions::*;
 use crate::machine::disjuncts::VarData;
 use crate::parser::ast::*;
@@ -251,7 +251,7 @@ impl DebrayAllocator {
             }
         }
 
-        if self.branch_stack.len() > 0 {
+        if !self.branch_stack.is_empty() {
             for var_num in subsumed_hits {
                 self.branch_stack.add_branch_occurrence(var_num);
             }
@@ -534,7 +534,9 @@ impl DebrayAllocator {
             VarAlloc::Temp { safety, .. } => {
                 *safety = VarSafetyStatus::unneeded(branch_designator);
             }
-            _ => unreachable!(),
+            _ => {
+                unreachable!()
+            }
         }
     }
 
@@ -679,7 +681,7 @@ impl Allocator for DebrayAllocator {
         lvl: Level,
         term_loc: GenContext,
         code: &mut CodeDeque,
-    ) {
+    ) -> RegType {
         let r = RegType::Temp(self.alloc_reg_to_non_var());
 
         match lvl {
@@ -696,6 +698,8 @@ impl Allocator for DebrayAllocator {
                 code.push_back(Target::argument_to_variable(r, k));
             }
         };
+
+        r
     }
 
     fn mark_non_var<'a, Target: CompilationTarget<'a>>(

src/ffi.rs

@@ -324,7 +324,7 @@ impl ForeignFunctionTable {
         let mut pointer_args =
             Self::build_pointer_args(&mut args, &function_impl.args, &mut self.structs)?;
 
-        return unsafe {
+        unsafe {
             macro_rules! call_and_return {
                 ($type:ty) => {{
                     let mut n: Box<u8> = Box::new(0);
@@ -410,7 +410,7 @@ impl ForeignFunctionTable {
                 }
                 _ => unreachable!(),
             }
-        };
+        }
     }
 
     fn read_struct(
@@ -517,7 +517,7 @@ impl Value {
     fn as_ptr(&mut self) -> Result<*mut c_void, FFIError> {
         match self {
             Value::CString(ref mut cstr) => Ok(&mut *cstr as *mut _ as *mut c_void),
-            Value::Int(n) => Ok(*n as *mut c_void),
+            Value::Int(n) => Ok(std::ptr::with_exposed_provenance_mut(*n as usize)),
             _ => Err(FFIError::ValueCast),
         }
     }

src/forms.rs

@@ -1,11 +1,12 @@
 use crate::arena::*;
 use crate::atom_table::*;
+use crate::functor_macro::*;
 use crate::instructions::*;
 use crate::machine::disjuncts::VarData;
-use crate::machine::heap::*;
 use crate::machine::loader::PredicateQueue;
 use crate::machine::machine_errors::*;
 use crate::machine::machine_indices::*;
+use crate::offset_table::OffsetTable;
 use crate::parser::ast::*;
 use crate::parser::dashu::{Integer, Rational};
 use crate::parser::parser::CompositeOpDesc;
@@ -26,18 +27,6 @@ use std::path::PathBuf;
 
 pub type PredicateKey = (Atom, usize); // name, arity.
 
-/*
-// vars of predicate, toplevel offset.  Vec<Term> is always a vector
-// of vars (we get their adjoining cells this way).
-pub type JumpStub = Vec<Term>;
-*/
-
-#[derive(Debug)]
-pub enum TopLevel {
-    Fact(Fact, VarData), // Term, line_num, col_num
-    Rule(Rule, VarData), // Rule, line_num, col_num
-}
-
 #[derive(Debug, Clone, Copy)]
 pub enum AppendOrPrepend {
     Append,
@@ -82,6 +71,28 @@ pub enum CallPolicy {
     Counted,
 }
 
+#[derive(Debug, Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Hash)]
+pub enum GenContext {
+    Head,
+    Mid(usize),
+    Last(usize), // Mid & Last: chunk_num
+}
+
+impl GenContext {
+    #[inline]
+    pub fn chunk_num(&self) -> usize {
+        match self {
+            GenContext::Head => 0,
+            &GenContext::Mid(cn) | &GenContext::Last(cn) => cn,
+        }
+    }
+
+    #[inline]
+    pub fn is_last(self) -> bool {
+        matches!(self, GenContext::Last(_))
+    }
+}
+
 #[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
 pub enum ChunkType {
     Head,
@@ -121,7 +132,7 @@ impl ChunkType {
 #[derive(Debug)]
 pub enum ChunkedTerms {
     Branch(Vec<VecDeque<ChunkedTerms>>),
-    Chunk(VecDeque<QueryTerm>),
+    Chunk { terms: VecDeque<QueryTerm> },
 }
 
 #[derive(Debug)]
@@ -161,22 +172,30 @@ impl ChunkedTermVec {
 
     #[inline]
     pub fn add_chunk(&mut self) {
-        self.chunk_vec
+        let chunk = ChunkedTerms::Chunk {
-            .push_back(ChunkedTerms::Chunk(VecDeque::from(vec![])));
+            terms: VecDeque::from(vec![]),
+        };
+        self.chunk_vec.push_back(chunk);
     }
 
     pub fn push_chunk_term(&mut self, term: QueryTerm) {
         match self.chunk_vec.back_mut() {
             Some(ChunkedTerms::Branch(_)) => {
-                self.chunk_vec
+                let chunk = ChunkedTerms::Chunk {
-                    .push_back(ChunkedTerms::Chunk(VecDeque::from(vec![term])));
+                    terms: VecDeque::from(vec![term]),
+                };
+
+                self.chunk_vec.push_back(chunk);
             }
-            Some(ChunkedTerms::Chunk(chunk)) => {
+            Some(ChunkedTerms::Chunk { terms, .. }) => {
-                chunk.push_back(term);
+                terms.push_back(term);
             }
             None => {
-                self.chunk_vec
+                let chunk = ChunkedTerms::Chunk {
-                    .push_back(ChunkedTerms::Chunk(VecDeque::from(vec![term])));
+                    terms: VecDeque::from(vec![term]),
+                };
+
+                self.chunk_vec.push_back(chunk);
             }
         }
     }
@@ -353,9 +372,9 @@ pub enum ModuleSource {
 
 impl ModuleSource {
     pub(crate) fn as_functor_stub(&self) -> MachineStub {
-        match self {
+        match *self {
             ModuleSource::Library(name) => {
-                functor!(atom!("library"), [atom(name)])
+                functor!(atom!("library"), [atom_as_cell(name)])
             }
             ModuleSource::File(name) => {
                 functor!(name)
@@ -608,9 +627,9 @@ impl Default for Number {
 impl fmt::Display for Number {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         match self {
-            Number::Float(fl) => write!(f, "{}", fl),
+            Number::Float(fl) => write!(f, "{fl}"),
-            Number::Integer(n) => write!(f, "{}", n),
+            Number::Integer(n) => write!(f, "{n}"),
-            Number::Rational(r) => write!(f, "{}", r),
+            Number::Rational(r) => write!(f, "{r}"),
             Number::Fixnum(n) => write!(f, "{}", n.get_num()),
         }
     }
@@ -679,17 +698,18 @@ impl ArenaFrom<isize> for Number {
 impl ArenaFrom<u32> for Number {
     #[inline]
     fn arena_from(value: u32, _arena: &mut Arena) -> Number {
-        Number::Fixnum(Fixnum::build_with(value as i64))
+        Number::Fixnum(Fixnum::build_with(value))
     }
 }
 
 impl ArenaFrom<i32> for Number {
     #[inline]
     fn arena_from(value: i32, _arena: &mut Arena) -> Number {
-        Number::Fixnum(Fixnum::build_with(value as i64))
+        Number::Fixnum(Fixnum::build_with(value))
     }
 }
 
+/*
 impl ArenaFrom<Number> for Literal {
     #[inline]
     fn arena_from(value: Number, arena: &mut Arena) -> Literal {
@@ -701,6 +721,21 @@ impl ArenaFrom<Number> for Literal {
         }
     }
 }
+*/
+
+impl ArenaFrom<u64> for HeapCellValue {
+    #[inline]
+    fn arena_from(value: u64, arena: &mut Arena) -> HeapCellValue {
+        HeapCellValue::from(fixnum!(Literal, value as i64, arena))
+    }
+}
+
+impl ArenaFrom<usize> for HeapCellValue {
+    #[inline]
+    fn arena_from(value: usize, arena: &mut Arena) -> HeapCellValue {
+        HeapCellValue::arena_from(value as u64, arena)
+    }
+}
 
 impl ArenaFrom<Number> for HeapCellValue {
     #[inline]
@@ -708,7 +743,7 @@ impl ArenaFrom<Number> for HeapCellValue {
         match value {
             Number::Fixnum(n) => fixnum_as_cell!(n),
             Number::Integer(n) => typed_arena_ptr_as_cell!(n),
-            Number::Float(OrderedFloat(n)) => HeapCellValue::from(float_alloc!(n, arena)),
+            Number::Float(n) => HeapCellValue::from(arena.f64_tbl.build_with(n)),
             Number::Rational(n) => typed_arena_ptr_as_cell!(n),
         }
     }
@@ -771,10 +806,10 @@ impl Number {
     }
 }
 
-#[derive(Debug, Clone)]
+#[derive(Debug, Copy, Clone)]
 pub(crate) enum OptArgIndexKey {
-    Literal(usize, usize, Literal, Vec<Literal>), // index, IndexingCode location, opt arg, alternatives
+    Literal(usize, usize, Literal, Option<Literal>), // index, IndexingCode location, opt arg, alternatives
-    List(usize, usize),                           // index, IndexingCode location
+    List(usize, usize),                              // index, IndexingCode location
     None,
     Structure(usize, usize, Atom, usize), // index, IndexingCode location, name, arity
 }

src/functor_macro.rs

@@ -0,0 +1,798 @@
+//! A macro to construct functor terms ready to be written to the WAM
+//! heap.
+
+use crate::atom_table::*;
+use crate::instructions::IndexingCodePtr;
+use crate::machine::heap::Heap;
+use crate::parser::ast::Fixnum;
+use crate::types::*;
+
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub(crate) enum FunctorElement {
+    AbsoluteCell(HeapCellValue),
+    Cell(HeapCellValue),
+    InnerFunctor(u64, Vec<FunctorElement>),
+    String(u64, String),
+}
+
+// helper macros
+macro_rules! count {
+    () => (0);
+    ( $x:tt $($xs:tt)* ) => (1 + count!($($xs)*));
+}
+
+// core macros
+
+/*
+ * functor! is more declarative now, with fewer effects and more
+ * work done at compile time using const functions. With these
+ * advantages come new quirks: expressions must generally be wrapped
+ * in round parentheses for rustc to parse them. See the tests module
+ * below for examples, especially those involving atom!
+ * subexpressions.
+ */
+
+macro_rules! functor {
+    ($name:expr) => ({
+        vec![FunctorElement::Cell(atom_as_cell!($name))]
+    });
+    ($name:expr, [$($dt:ident($($value:tt),*)),+]) => ({
+        build_functor!([$($dt($($value),*)),*],
+                       [FunctorElement::Cell(atom_as_cell!($name, count!($($dt) *)))],
+                       1,
+                       [])
+    });
+}
+
+macro_rules! inner_functor {
+    ($name:expr, $res_len:expr, [$($dt:ident($($value:tt),*)),+]) => ({
+        build_functor!([$($dt($($value),*)),*],
+                       [FunctorElement::Cell(atom_as_cell!($name, count!($($dt) *)))],
+                       1 + $res_len,
+                       [])
+    });
+}
+
+macro_rules! build_functor {
+    ([], [$($res:expr),*], $res_len:expr, [$($subfunctor:expr),*]) => ({
+        vec![$($res,)* $($subfunctor),*]
+    });
+    ([indexing_code_ptr($e:expr) $(, $dt:ident($($value:tt),*))*],
+     [$($res:expr),*],
+     $res_len:expr,
+     [$($subfunctor:expr),*]) => ({
+        let (inner_functor, cell_size) = indexing_code_ptr($e);
+        let referent = if cell_size == 1 {
+            heap_loc_as_cell!(1u64 + count!($($dt)*) + $res_len)
+        } else {
+            str_loc_as_cell!(1u64 + count!($($dt)*) + $res_len)
+        };
+
+        build_functor!([$($dt($($value),*)),*],
+                       [$($res, )* FunctorElement::Cell(referent)],
+                       1 + cell_size + $res_len,
+                       [$($subfunctor, )* FunctorElement::InnerFunctor(cell_size, inner_functor)])
+    });
+    ([fixnum($e:expr) $(, $dt:ident($($value:tt),*))*],
+     [$($res:expr),*],
+     $res_len:expr,
+     [$($subfunctor:expr),*]) => ({
+         build_functor!([$($dt($($value),*)),*],
+                        [$($res, )* FunctorElement::Cell(fixnum_as_cell!(/*FIXME this is not safe*/ unsafe{Fixnum::build_with_unchecked($e as i64)}))],
+                        1 + $res_len,
+                        [$($subfunctor),*])
+    });
+    ([cell($e:expr) $(, $dt:ident($($value:tt),*))*],
+     [$($res:expr),*],
+     $res_len:expr,
+     [$($subfunctor:expr),*]) => ({
+         build_functor!([$($dt($($value),*)),*],
+                        [$($res, )* FunctorElement::AbsoluteCell($e)],
+                        1 + $res_len,
+                        [$($subfunctor),*])
+    });
+    ([literal($e:expr) $(, $dt:ident($($value:tt),*))*],
+     [$($res:expr),*],
+     $res_len:expr,
+     [$($subfunctor:expr),*]) => ({
+         build_functor!([$($dt($($value),*)),*],
+                        [$($res, )* FunctorElement::AbsoluteCell(HeapCellValue::from($e))],
+                        1 + $res_len,
+                        [$($subfunctor),*])
+    });
+    ([number($n:expr, $arena:expr) $(, $dt:ident($($value:tt),*))*],
+     [$($res:expr),*],
+     $res_len:expr,
+     [$($subfunctor:expr),*]) => ({
+         let number_cell = HeapCellValue::arena_from($n, $arena);
+
+         build_functor!([$($dt($($value),*)),*],
+                        [$($res, )* FunctorElement::Cell(number_cell)],
+                        1 + $res_len,
+                        [$($subfunctor),*])
+    });
+    ([list([]) $(, $dt:ident($($value:tt),*))*],
+     [$($res:expr),*],
+     $res_len:expr,
+     [$($subfunctor:expr),*]) => ({
+        build_functor!([$($dt($($value),*)),*],
+                       [$($res, )* FunctorElement::Cell(empty_list_as_cell!())],
+                       1 + $res_len,
+                       [$($subfunctor),*])
+    });
+    ([list([$id:ident($($id_value:tt),*) $(, $in_dt:ident($($in_value:tt),*))*]) $(, $dt:ident($($value:tt),*))*],
+     [$($res:expr),*],
+     $res_len:expr,
+     [$($subfunctor:expr),*]) => ({
+        build_functor!([functor((atom!(".")), [$id($($id_value),*), list([$($in_dt($($in_value),*)),*])])
+                        $(, $dt($($value),*))*],
+                       [$($res),*],
+                       $res_len,
+                       [$($subfunctor),*])
+    });
+    ([string($s:expr) $(, $dt:ident($($value:tt),*))*], [$($res:expr),*], $res_len:expr, [$($subfunctor:expr),*]) => ({
+        #[allow(unused_parens)]
+        let string = $s;
+        let pstr_len = cell_index!(Heap::compute_pstr_size(&string)) as u64;
+        let result_len = 1 + count!($($dt)*) + $res_len;
+
+        build_functor!([$($dt($($value),*)),*],
+                       [$($res, )* FunctorElement::Cell(pstr_loc_as_cell!(heap_index!(result_len as usize) as u64))],
+                       1 + $res_len + pstr_len,
+                       [$($subfunctor, )* FunctorElement::String(pstr_len, string)])
+    });
+    ([atom_as_cell($n:expr) $(, $dt:ident($($value:tt),*))*], [$($res:expr),*], $res_len:expr, [$($subfunctor:expr),*]) => ({
+        build_functor!([$($dt($($value),*)),*],
+                       [$($res, )* FunctorElement::Cell(atom_as_cell!($n))],
+                       1 + $res_len,
+                       [$($subfunctor),*])
+    });
+    ([functor($stub:expr) $(, $dt:ident($($value:tt),*))*], [$($res:expr),*], $res_len:expr, [$($subfunctor:expr),*]) => ({
+        let result_len = 1u64 + count!($($dt)*) + $res_len;
+        let inner_functor_size = cell_index!(Heap::compute_functor_byte_size(&$stub)) as u64;
+
+        build_functor!([$($dt($($value),*)),*],
+                       [$($res, )* FunctorElement::Cell(str_loc_as_cell!(result_len))],
+                       1 + $res_len + inner_functor_size,
+                       [$($subfunctor, )*
+                        FunctorElement::InnerFunctor(inner_functor_size, $stub)])
+    });
+    ([$id:ident($n:expr) $(, $dt:ident($($value:tt),*))*], [$($res:expr),*], $res_len:expr, [$($subfunctor:expr),*]) => ({
+        build_functor!([$($dt($($value),*)),*],
+                       [$($res, )* FunctorElement::Cell($id!($n))],
+                       1 + $res_len,
+                       [$($subfunctor),*])
+    });
+    ([functor($name:expr, [$($in_dt:ident($($in_value:tt),*)),+]) $(, $dt:ident($($value:tt),*))*],
+     [$($res:expr),*],
+     $res_len:expr,
+     [$($subfunctor:expr),*]) => ({
+         let result_len = 1u64 + count!($($dt)*) + $res_len;
+         let inner_functor = inner_functor!($name, 0, [$($in_dt($($in_value),*)),*]);
+         let inner_functor_size = cell_index!(Heap::compute_functor_byte_size(&inner_functor)) as u64;
+
+         build_functor!([$($dt($($value),*)),*],
+                        [$($res, )* FunctorElement::Cell(str_loc_as_cell!(result_len))],
+                        1 + $res_len + inner_functor_size,
+                        [$($subfunctor, )*
+                         FunctorElement::InnerFunctor(inner_functor_size, inner_functor)])
+    });
+}
+
+pub(crate) fn indexing_code_ptr(code_ptr: IndexingCodePtr) -> (Vec<FunctorElement>, u64) {
+    match code_ptr {
+        IndexingCodePtr::DynamicExternal(o) => {
+            (functor!(atom!("dynamic_external"), [fixnum(o)]), 2)
+        }
+        IndexingCodePtr::External(o) => (functor!(atom!("external"), [fixnum(o)]), 2),
+        IndexingCodePtr::Internal(o) => (functor!(atom!("internal"), [fixnum(o)]), 2),
+        IndexingCodePtr::Fail => (vec![FunctorElement::Cell(atom_as_cell!(atom!("fail")))], 1),
+    }
+}
+
+pub(crate) fn variadic_functor(
+    name: Atom,
+    arity: usize,
+    iter: impl Iterator<Item = Vec<FunctorElement>>,
+) -> Vec<FunctorElement> {
+    let mut arg_vec = vec![
+        FunctorElement::Cell(atom_as_cell!(name, arity)),
+        FunctorElement::Cell(list_loc_as_cell!(2)),
+    ];
+
+    let key_value_pairs: Vec<_> = iter.collect();
+    let num_items = key_value_pairs.len();
+    let mut functor_offset = 0;
+
+    for (idx, kv_func) in key_value_pairs.iter().enumerate() {
+        let functor_size = cell_index!(Heap::compute_functor_byte_size(kv_func));
+
+        arg_vec.push(FunctorElement::Cell(str_loc_as_cell!(
+            2 + num_items * 2 + functor_offset
+        )));
+        arg_vec.push(FunctorElement::Cell(list_loc_as_cell!(4 + 2 * idx)));
+
+        functor_offset += functor_size;
+    }
+
+    arg_vec.pop();
+    arg_vec.push(FunctorElement::Cell(empty_list_as_cell!()));
+
+    arg_vec.extend(key_value_pairs.into_iter().map(|kv_func| {
+        let inner_functor_size = cell_index!(Heap::compute_functor_byte_size(&kv_func));
+        FunctorElement::InnerFunctor(inner_functor_size as u64, kv_func)
+    }));
+
+    arg_vec
+}
+
+#[cfg(test)]
+#[allow(unused_parens)]
+mod tests {
+    use super::*;
+    use indexmap::indexmap;
+    use std::string::String;
+    use FunctorElement::*;
+
+    #[test]
+    fn basic_terms() {
+        let functor = functor!(
+            atom!("first"),
+            [atom_as_cell((atom!("a"))), char_as_cell('c')]
+        );
+
+        assert_eq!(functor.len(), 3);
+
+        assert_eq!(functor[0], Cell(atom_as_cell!(atom!("first"), 2)));
+        assert_eq!(functor[1], Cell(atom_as_cell!(atom!("a"))));
+        assert_eq!(functor[2], Cell(char_as_cell!('c')));
+
+        let functor = functor!(
+            atom!("second"),
+            [
+                atom_as_cell((atom!("a"))),
+                functor((atom!("b")), [fixnum(1), fixnum(2)]),
+                char_as_cell('c')
+            ]
+        );
+
+        assert_eq!(functor.len(), 5);
+
+        assert_eq!(functor[0], Cell(atom_as_cell!(atom!("second"), 3)));
+        assert_eq!(functor[1], Cell(atom_as_cell!(atom!("a"))));
+        assert_eq!(functor[2], Cell(str_loc_as_cell!(4)));
+        assert_eq!(functor[3], Cell(char_as_cell!('c')));
+        assert_eq!(
+            functor[4],
+            InnerFunctor(3, functor!(atom!("b"), [fixnum(1), fixnum(2)]))
+        );
+
+        let functor = functor!(
+            atom!("third"),
+            [
+                atom_as_cell((atom!("a"))),
+                functor((atom!("b")), [fixnum(1), fixnum(2)]),
+                functor((atom!("c")), [fixnum(1), fixnum(2)]),
+                char_as_cell('c')
+            ]
+        );
+
+        assert_eq!(functor.len(), 7);
+
+        assert_eq!(functor[0], Cell(atom_as_cell!(atom!("third"), 4)));
+        assert_eq!(functor[1], Cell(atom_as_cell!(atom!("a"))));
+        assert_eq!(functor[2], Cell(str_loc_as_cell!(5)));
+        assert_eq!(functor[3], Cell(str_loc_as_cell!(8)));
+        assert_eq!(functor[4], Cell(char_as_cell!('c')));
+        assert_eq!(
+            functor[5],
+            InnerFunctor(3, functor!(atom!("b"), [fixnum(1), fixnum(2)]))
+        );
+        assert_eq!(
+            functor[6],
+            InnerFunctor(3, functor!(atom!("c"), [fixnum(1), fixnum(2)]))
+        );
+
+        let functor = functor!(
+            atom!("fourth"),
+            [
+                atom_as_cell((atom!("a"))),
+                functor((atom!("b")), [fixnum(1), fixnum(2)]),
+                functor((atom!("c")), [fixnum(1)]),
+                functor((atom!("d")), [fixnum(453), fixnum(2)]),
+                char_as_cell('c')
+            ]
+        );
+
+        assert_eq!(functor.len(), 9);
+
+        assert_eq!(functor[0], Cell(atom_as_cell!(atom!("fourth"), 5)));
+        assert_eq!(functor[1], Cell(atom_as_cell!(atom!("a"))));
+        assert_eq!(functor[2], Cell(str_loc_as_cell!(6)));
+        assert_eq!(functor[3], Cell(str_loc_as_cell!(9)));
+        assert_eq!(functor[4], Cell(str_loc_as_cell!(11)));
+        assert_eq!(functor[5], Cell(char_as_cell!('c')));
+        assert_eq!(
+            functor[6],
+            InnerFunctor(3, functor!(atom!("b"), [fixnum(1), fixnum(2)]))
+        );
+        assert_eq!(
+            functor[7],
+            InnerFunctor(2, functor!(atom!("c"), [fixnum(1)]))
+        );
+        assert_eq!(
+            functor[8],
+            InnerFunctor(3, functor!(atom!("d"), [fixnum(453), fixnum(2)]))
+        );
+    }
+
+    #[test]
+    fn basic_terms_in_heap() {
+        let functor = functor!(
+            atom!("first"),
+            [atom_as_cell((atom!("a"))), char_as_cell('b')]
+        );
+
+        assert_eq!(functor.len(), 3);
+
+        let mut heap = Heap::new();
+        let mut functor_writer = Heap::functor_writer(functor);
+        let loc = functor_writer(&mut heap).unwrap();
+
+        assert_eq!(loc, str_loc_as_cell!(0));
+
+        assert_eq!(heap[0], atom_as_cell!(atom!("first"), 2));
+        assert_eq!(heap[1], atom_as_cell!(atom!("a")));
+        assert_eq!(heap[2], char_as_cell!('b'));
+
+        heap.truncate(2);
+
+        let functor = functor!(
+            atom!("second"),
+            [
+                atom_as_cell((atom!("a"))),
+                functor((atom!("b")), [fixnum(1), fixnum(2)]),
+                functor((atom!("c")), [fixnum(1), fixnum(2)]),
+                char_as_cell('b')
+            ]
+        );
+
+        assert_eq!(functor.len(), 7);
+
+        let mut functor_writer = Heap::functor_writer(functor);
+        let loc = functor_writer(&mut heap).unwrap();
+
+        assert_eq!(loc, str_loc_as_cell!(2));
+
+        assert_eq!(heap[2], atom_as_cell!(atom!("second"), 4));
+        assert_eq!(heap[3], atom_as_cell!(atom!("a")));
+        assert_eq!(heap[4], str_loc_as_cell!(7));
+        assert_eq!(heap[5], str_loc_as_cell!(10));
+        assert_eq!(heap[6], char_as_cell!('b'));
+        assert_eq!(heap[7], atom_as_cell!(atom!("b"), 2));
+        assert_eq!(heap[8], fixnum_as_cell!(Fixnum::build_with(1)));
+        assert_eq!(heap[9], fixnum_as_cell!(Fixnum::build_with(2)));
+        assert_eq!(heap[10], atom_as_cell!(atom!("c"), 2));
+        assert_eq!(heap[11], fixnum_as_cell!(Fixnum::build_with(1)));
+        assert_eq!(heap[12], fixnum_as_cell!(Fixnum::build_with(2)));
+    }
+
+    #[test]
+    fn nested_functors() {
+        let functor = functor!(
+            atom!("first"),
+            [
+                atom_as_cell((atom!("a"))),
+                functor(
+                    (atom!("d")),
+                    [
+                        fixnum(1),
+                        functor(
+                            (atom!("b")),
+                            [atom_as_cell((atom!("c"))), char_as_cell('c')]
+                        )
+                    ]
+                ),
+                functor((atom!("e")), [fixnum(453), fixnum(2)]),
+                char_as_cell('b')
+            ]
+        );
+
+        assert_eq!(functor.len(), 7);
+
+        assert_eq!(functor[0], Cell(atom_as_cell!(atom!("first"), 4)));
+        assert_eq!(functor[1], Cell(atom_as_cell!(atom!("a"))));
+        assert_eq!(functor[2], Cell(str_loc_as_cell!(5)));
+        assert_eq!(functor[3], Cell(str_loc_as_cell!(11)));
+        assert_eq!(functor[4], Cell(char_as_cell!('b')));
+        assert_eq!(
+            functor[5],
+            InnerFunctor(
+                6,
+                vec![
+                    Cell(atom_as_cell!(atom!("d"), 2)),
+                    Cell(fixnum_as_cell!(Fixnum::build_with(1))),
+                    Cell(str_loc_as_cell!(3)),
+                    InnerFunctor(
+                        3,
+                        functor!(atom!("b"), [atom_as_cell((atom!("c"))), char_as_cell('c')])
+                    )
+                ]
+            )
+        );
+        assert_eq!(
+            functor[6],
+            InnerFunctor(3, functor!(atom!("e"), [fixnum(453), fixnum(2)]))
+        );
+    }
+
+    #[test]
+    fn nested_functors_in_heap() {
+        let functor = functor!(
+            atom!("first"),
+            [
+                atom_as_cell((atom!("a"))),
+                functor(
+                    (atom!("second")),
+                    [
+                        fixnum(1),
+                        functor(
+                            (atom!("third")),
+                            [atom_as_cell((atom!("b"))), char_as_cell('c')]
+                        )
+                    ]
+                ),
+                functor((atom!("fourth")), [fixnum(453), fixnum(2)]),
+                char_as_cell('b')
+            ]
+        );
+
+        let mut heap = Heap::new();
+        let mut functor_writer = Heap::functor_writer(functor);
+        let loc = functor_writer(&mut heap).unwrap();
+
+        assert_eq!(loc, str_loc_as_cell!(0));
+
+        assert_eq!(heap.cell_len(), 14);
+
+        assert_eq!(heap[0], atom_as_cell!(atom!("first"), 4));
+        assert_eq!(heap[1], atom_as_cell!(atom!("a")));
+        assert_eq!(heap[2], str_loc_as_cell!(5));
+        assert_eq!(heap[3], str_loc_as_cell!(11));
+        assert_eq!(heap[4], char_as_cell!('b'));
+        assert_eq!(heap[5], atom_as_cell!(atom!("second"), 2));
+        assert_eq!(heap[6], fixnum_as_cell!(Fixnum::build_with(1)));
+        assert_eq!(heap[7], str_loc_as_cell!(8));
+        assert_eq!(heap[8], atom_as_cell!(atom!("third"), 2));
+        assert_eq!(heap[9], atom_as_cell!(atom!("b")));
+        assert_eq!(heap[10], char_as_cell!('c'));
+        assert_eq!(heap[11], atom_as_cell!(atom!("fourth"), 2));
+        assert_eq!(heap[12], fixnum_as_cell!(Fixnum::build_with(453)));
+        assert_eq!(heap[13], fixnum_as_cell!(Fixnum::build_with(2)));
+    }
+
+    #[test]
+    fn functors_with_strings_in_heap() {
+        let functor = functor!(atom!("first"), [string((String::from("a string")))]);
+
+        assert_eq!(functor.len(), 3);
+
+        let mut heap = Heap::new();
+        let mut functor_writer = Heap::functor_writer(functor);
+        let loc = functor_writer(&mut heap).unwrap();
+
+        assert_eq!(loc, str_loc_as_cell!(0));
+        assert_eq!(heap.cell_len(), 5);
+
+        assert_eq!(heap[0], atom_as_cell!(atom!("first"), 1));
+        assert_eq!(heap[1], pstr_loc_as_cell!(heap_index!(2)));
+        assert_eq!(
+            heap.slice_to_str(heap_index!(2), "a string".len()),
+            "a string"
+        );
+        assert_eq!(heap[4], empty_list_as_cell!());
+
+        heap.truncate(0);
+
+        let functor = functor!(
+            atom!("second"),
+            [string((String::from("a stuttered\0 string")))]
+        );
+
+        let mut functor_writer = Heap::functor_writer(functor);
+        functor_writer(&mut heap).unwrap();
+
+        assert_eq!(heap.cell_len(), 10);
+
+        assert_eq!(heap[0], atom_as_cell!(atom!("second"), 1));
+        assert_eq!(heap[1], pstr_loc_as_cell!(heap_index!(2)));
+        assert_eq!(
+            heap.slice_to_str(heap_index!(2), "a stuttered".len()),
+            "a stuttered"
+        );
+        assert_eq!(heap[4], list_loc_as_cell!(5));
+        assert_eq!(heap[5], char_as_cell!('\u{0}'));
+        assert_eq!(heap[6], pstr_loc_as_cell!(heap_index!(7)));
+        assert_eq!(
+            heap.slice_to_str(heap_index!(7), " string".len()),
+            " string"
+        );
+        assert_eq!(heap[9], empty_list_as_cell!());
+    }
+
+    #[test]
+    fn functors_with_lists_in_heap() {
+        let functor = functor!(
+            atom!("first"),
+            [list([fixnum(1), atom_as_cell((atom!("a"))), fixnum(2)])]
+        );
+
+        assert_eq!(functor.len(), 3);
+
+        let mut heap = Heap::new();
+        let mut functor_writer = Heap::functor_writer(functor);
+
+        functor_writer(&mut heap).unwrap();
+
+        assert_eq!(heap.cell_len(), 11);
+
+        assert_eq!(heap[0], atom_as_cell!(atom!("first"), 1));
+        assert_eq!(heap[1], str_loc_as_cell!(2));
+        assert_eq!(heap[2], atom_as_cell!(atom!("."), 2));
+        assert_eq!(heap[3], fixnum_as_cell!(Fixnum::build_with(1)));
+        assert_eq!(heap[4], str_loc_as_cell!(5));
+        assert_eq!(heap[5], atom_as_cell!(atom!("."), 2));
+        assert_eq!(heap[6], atom_as_cell!(atom!("a")));
+        assert_eq!(heap[7], str_loc_as_cell!(8));
+        assert_eq!(heap[8], atom_as_cell!(atom!("."), 2));
+        assert_eq!(heap[9], fixnum_as_cell!(Fixnum::build_with(2)));
+        assert_eq!(heap[10], empty_list_as_cell!());
+    }
+
+    #[test]
+    fn inlined_atoms() {
+        let atom_table = AtomTable::new();
+        let inlined = AtomTable::build_with(&atom_table, "inline");
+
+        assert!(inlined.is_inlined());
+        assert_eq!(&*inlined.as_str(), "inline");
+
+        let non_inlined = AtomTable::build_with(&atom_table, "longer non-inlined atom");
+
+        assert!(!non_inlined.is_inlined());
+        assert_eq!(&*non_inlined.as_str(), "longer non-inlined atom");
+    }
+
+    #[test]
+    fn functors_with_indexing_code_ptr() {
+        let code_ptr = IndexingCodePtr::Internal(0);
+        let functor = functor!(
+            atom!("first"),
+            [
+                string((String::from("a string"))),
+                indexing_code_ptr(code_ptr)
+            ]
+        );
+
+        let mut heap = Heap::new();
+        let mut functor_writer = Heap::functor_writer(functor);
+
+        functor_writer(&mut heap).unwrap();
+
+        assert_eq!(heap.cell_len(), 8);
+
+        assert_eq!(heap[0], atom_as_cell!(atom!("first"), 2));
+        assert_eq!(heap[1], pstr_loc_as_cell!(heap_index!(3)));
+        assert_eq!(heap[2], str_loc_as_cell!(6));
+        assert_eq!(
+            heap.slice_to_str(heap_index!(3), "a string".len()),
+            "a string"
+        );
+        assert_eq!(heap[5], empty_list_as_cell!());
+        assert_eq!(heap[6], atom_as_cell!(atom!("internal"), 1));
+        assert_eq!(heap[7], fixnum_as_cell!(Fixnum::build_with(0)));
+
+        heap.truncate(0);
+
+        let functor = functor!(
+            atom!("second"),
+            [
+                string((String::from("a string"))),
+                functor(
+                    (atom!("third")),
+                    [
+                        atom_as_cell((atom!("a"))),
+                        string((String::from("another string"))),
+                        indexing_code_ptr(code_ptr)
+                    ]
+                )
+            ]
+        );
+
+        let mut functor_writer = Heap::functor_writer(functor);
+        functor_writer(&mut heap).unwrap();
+
+        assert_eq!(heap.cell_len(), 15);
+
+        assert_eq!(heap[0], atom_as_cell!(atom!("second"), 2));
+        assert_eq!(heap[1], pstr_loc_as_cell!(heap_index!(3)));
+        assert_eq!(heap[2], str_loc_as_cell!(6));
+        assert_eq!(
+            heap.slice_to_str(heap_index!(3), "a string".len()),
+            "a string"
+        );
+        assert_eq!(heap[5], empty_list_as_cell!());
+        assert_eq!(heap[6], atom_as_cell!(atom!("third"), 3));
+        assert_eq!(heap[7], atom_as_cell!(atom!("a")));
+        assert_eq!(heap[8], pstr_loc_as_cell!(heap_index!(10)));
+        assert_eq!(heap[9], str_loc_as_cell!(13));
+        assert_eq!(
+            heap.slice_to_str(heap_index!(10), "another string".len()),
+            "another string"
+        );
+        assert_eq!(heap[12], empty_list_as_cell!());
+        assert_eq!(heap[13], atom_as_cell!(atom!("internal"), 1));
+        assert_eq!(heap[14], fixnum_as_cell!(Fixnum::build_with(0)));
+
+        let functor = functor!(
+            atom!("fourth"),
+            [
+                string((String::from("a string"))),
+                functor(
+                    (atom!("a")),
+                    [
+                        functor(
+                            (atom!("fifth")),
+                            [
+                                fixnum(5),
+                                string((String::from("another string"))),
+                                indexing_code_ptr(code_ptr)
+                            ]
+                        ),
+                        string((String::from("and another")))
+                    ]
+                )
+            ]
+        );
+
+        heap.truncate(0);
+
+        let mut functor_writer = Heap::functor_writer(functor);
+        functor_writer(&mut heap).unwrap();
+
+        assert_eq!(heap.cell_len(), 21);
+
+        assert_eq!(heap[0], atom_as_cell!(atom!("fourth"), 2));
+        assert_eq!(heap[1], pstr_loc_as_cell!(heap_index!(3)));
+        assert_eq!(heap[2], str_loc_as_cell!(6));
+        assert_eq!(
+            heap.slice_to_str(heap_index!(3), "a string".len()),
+            "a string"
+        );
+        assert_eq!(heap[5], empty_list_as_cell!());
+        assert_eq!(heap[6], atom_as_cell!(atom!("a"), 2));
+        assert_eq!(heap[7], str_loc_as_cell!(9));
+        assert_eq!(heap[8], pstr_loc_as_cell!(heap_index!(18))); // <-- wrong!
+        assert_eq!(heap[9], atom_as_cell!(atom!("fifth"), 3));
+        assert_eq!(heap[10], fixnum_as_cell!(Fixnum::build_with(5)));
+        assert_eq!(heap[11], pstr_loc_as_cell!(heap_index!(13)));
+        assert_eq!(heap[12], str_loc_as_cell!(16));
+        assert_eq!(
+            heap.slice_to_str(heap_index!(13), "another string".len()),
+            "another string"
+        );
+        assert_eq!(heap[15], empty_list_as_cell!());
+        assert_eq!(heap[16], atom_as_cell!(atom!("internal"), 1));
+        assert_eq!(heap[17], fixnum_as_cell!(Fixnum::build_with(0)));
+        assert_eq!(
+            heap.slice_to_str(heap_index!(18), "and another".len()),
+            "and another"
+        );
+        assert_eq!(heap[20], empty_list_as_cell!());
+
+        let constants = indexmap![
+            atom_as_cell!(atom!("a")) => IndexingCodePtr::External(2),
+            atom_as_cell!(atom!("d")) => IndexingCodePtr::External(7),
+        ];
+
+        let functor = variadic_functor(
+            atom!("switch_on_constants"),
+            1,
+            constants
+                .iter()
+                .map(|(c, ptr)| functor!(atom!(":"), [cell((*c)), indexing_code_ptr((*ptr))])),
+        );
+
+        heap.truncate(0);
+
+        let mut functor_writer = Heap::functor_writer(functor);
+        functor_writer(&mut heap).unwrap();
+
+        assert_eq!(heap[0], atom_as_cell!(atom!("switch_on_constants"), 1));
+        assert_eq!(heap[1], list_loc_as_cell!(2));
+        assert_eq!(heap[2], str_loc_as_cell!(6));
+        assert_eq!(heap[3], list_loc_as_cell!(4));
+        assert_eq!(heap[4], str_loc_as_cell!(11));
+        assert_eq!(heap[5], empty_list_as_cell!());
+        assert_eq!(heap[6], atom_as_cell!(atom!(":"), 2));
+        assert_eq!(heap[7], atom_as_cell!(atom!("a")));
+        assert_eq!(heap[8], str_loc_as_cell!(9));
+        assert_eq!(heap[9], atom_as_cell!(atom!("external"), 1));
+        assert_eq!(heap[10], fixnum_as_cell!(Fixnum::build_with(2)));
+        assert_eq!(heap[11], atom_as_cell!(atom!(":"), 2));
+        assert_eq!(heap[12], atom_as_cell!(atom!("d")));
+        assert_eq!(heap[13], str_loc_as_cell!(14));
+        assert_eq!(heap[14], atom_as_cell!(atom!("external"), 1));
+        assert_eq!(heap[15], fixnum_as_cell!(Fixnum::build_with(7)));
+    }
+
+    #[test]
+    fn undefined_procedure_functor() {
+        // existence_error
+        let culprit = functor!(atom!("/"), [atom_as_cell((atom!("a"))), fixnum(1)]);
+
+        let stub = functor!(
+            atom!("existence_error"),
+            [
+                atom_as_cell((atom!("procedure"))),
+                functor((culprit.clone()))
+            ]
+        );
+
+        println!("{stub:?}");
+
+        // now the error form
+        let lineless_error_form = functor!(atom!("error"), [functor(stub), functor(culprit)]);
+
+        println!("{lineless_error_form:?}");
+
+        let mut heap = Heap::new();
+        let mut functor_writer = Heap::functor_writer(lineless_error_form);
+
+        functor_writer(&mut heap).unwrap();
+
+        assert_eq!(heap[0], atom_as_cell!(atom!("error"), 2));
+        assert_eq!(heap[1], str_loc_as_cell!(3));
+        assert_eq!(heap[2], str_loc_as_cell!(9));
+        assert_eq!(heap[3], atom_as_cell!(atom!("existence_error"), 2));
+        assert_eq!(heap[4], atom_as_cell!(atom!("procedure")));
+        assert_eq!(heap[5], str_loc_as_cell!(6)); // is str_loc_as_cell!(3)
+        assert_eq!(heap[6], atom_as_cell!(atom!("/"), 2));
+        assert_eq!(heap[7], atom_as_cell!(atom!("a")));
+        assert_eq!(heap[8], fixnum_as_cell!(Fixnum::build_with(1)));
+        assert_eq!(heap[9], atom_as_cell!(atom!("/"), 2));
+        assert_eq!(heap[10], atom_as_cell!(atom!("a")));
+        assert_eq!(heap[11], fixnum_as_cell!(Fixnum::build_with(1)));
+    }
+
+    #[test]
+    fn argless_functor() {
+        let name = functor!(atom!("[]"));
+
+        assert_eq!(name.len(), 1);
+
+        let mut heap = Heap::new();
+        let mut functor_writer = Heap::functor_writer(name);
+        let loc = functor_writer(&mut heap).unwrap();
+
+        assert_eq!(loc, heap_loc_as_cell!(0));
+    }
+
+    #[test]
+    fn predefined_subfunctors() {
+        let stub = functor!(atom!("sub"), [atom_as_cell((atom!("[]")))]);
+        let name = functor!(atom!("super"), [functor(stub)]);
+
+        let mut heap = Heap::new();
+        let mut functor_writer = Heap::functor_writer(name);
+
+        functor_writer(&mut heap).unwrap();
+
+        assert_eq!(heap.cell_len(), 4);
+
+        assert_eq!(heap[0], atom_as_cell!(atom!("super"), 1));
+        assert_eq!(heap[1], str_loc_as_cell!(2));
+        assert_eq!(heap[2], atom_as_cell!(atom!("sub"), 1));
+        assert_eq!(heap[3], empty_list_as_cell!());
+    }
+}

src/heap_print.rs

@@ -8,11 +8,10 @@ use crate::parser::dashu::{ibig, Integer, Rational};
 use crate::forms::*;
 use crate::heap_iter::*;
 use crate::machine::heap::*;
-use crate::machine::machine_indices::*;
-use crate::machine::machine_state::pstr_loc_and_offset;
 use crate::machine::partial_string::*;
 use crate::machine::stack::*;
 use crate::machine::streams::*;
+use crate::offset_table::*;
 use crate::types::*;
 
 use dashu::base::Signed;
@@ -25,7 +24,6 @@ use std::convert::TryFrom;
 use std::iter::once;
 use std::net::{IpAddr, TcpListener};
 use std::rc::Rc;
-use std::sync::Arc;
 
 /* contains the location, name, precision and Specifier of the parent op. */
 #[derive(Debug, Copy, Clone)]
@@ -206,11 +204,12 @@ impl NumberFocus {
 
 #[derive(Debug, Clone, Copy)]
 struct CommaSeparatedCharList {
-    pstr: PartialString,
+    // pstr: PartialString,
-    offset: usize,
+    // offset: usize,
+    pstr_loc: usize,
     max_depth: usize,
-    end_cell: HeapCellValue,
+    // end_cell: HeapCellValue,
-    end_h: Option<usize>,
+    // end_h: Option<usize>,
 }
 
 #[derive(Debug, Clone)]
@@ -389,17 +388,20 @@ fn is_numbered_var(name: Atom, arity: usize) -> bool {
 #[inline]
 fn negated_op_needs_bracketing(
     iter: &StackfulPreOrderHeapIter<ListElider>,
+    f64_tbl: &F64Table,
     op_dir: &OpDir,
     op: &Option<DirectedOp>,
 ) -> bool {
     if let Some(ref op) = op {
         op.is_negative_sign()
-            && iter.leftmost_leaf_has_property(op_dir, |addr| match Number::try_from(addr) {
+            && iter.leftmost_leaf_has_property(op_dir, |addr| {
-                Ok(Number::Fixnum(n)) => n.get_num() > 0,
+                match Number::try_from((addr, f64_tbl)) {
-                Ok(Number::Float(OrderedFloat(f))) => f > 0f64,
+                    Ok(Number::Fixnum(n)) => n.get_num() > 0,
-                Ok(Number::Integer(n)) => n.is_positive(),
+                    Ok(Number::Float(OrderedFloat(f))) => f > 0f64,
-                Ok(Number::Rational(n)) => n.is_positive(),
+                    Ok(Number::Integer(n)) => n.is_positive(),
-                _ => false,
+                    Ok(Number::Rational(n)) => n.is_positive(),
+                    _ => false,
+                }
             })
     } else {
         false
@@ -473,7 +475,7 @@ pub fn fmt_float(mut fl: f64) -> String {
 pub struct HCPrinter<'a, Outputter> {
     outputter: Outputter,
     iter: StackfulPreOrderHeapIter<'a, ListElider>,
-    atom_tbl: Arc<AtomTable>,
+    arena: &'a Arena,
     op_dir: &'a OpDir,
     state_stack: Vec<TokenOrRedirect>,
     toplevel_spec: Option<DirectedOp>,
@@ -488,9 +490,24 @@ pub struct HCPrinter<'a, Outputter> {
     pub double_quotes: bool,
 }
 
+fn ambiguity_check(
+    outputter: &impl HCValueOutputter,
+    quoted: bool,
+    last_item_idx: usize,
+    atom: &str,
+) -> bool {
+    let tail = &outputter.as_str()[last_item_idx..];
+
+    if atom == "," || !quoted || non_quoted_token(atom.chars()) {
+        requires_space(tail, atom)
+    } else {
+        requires_space(tail, "'")
+    }
+}
+
 macro_rules! push_space_if_amb {
     ($self:expr, $atom:expr, $action:block) => {
-        if $self.ambiguity_check($atom) {
+        if ambiguity_check(&$self.outputter, $self.quoted, $self.last_item_idx, $atom) {
             $self.outputter.push_char(' ');
             $action;
         } else {
@@ -516,28 +533,47 @@ pub(crate) fn numbervar(offset: &Integer, addr: HeapCellValue) -> Option<String>
         }
     }
 
-    match Number::try_from(addr) {
+    read_heap_cell!(addr,
-        Ok(Number::Fixnum(n)) if n.get_num() >= 0 => {
+        (HeapCellValueTag::Cons, c) => {
-            Some(numbervar(offset + Integer::from(n.get_num())))
+            match_untyped_arena_ptr!(c,
+               (ArenaHeaderTag::Integer, n) => {
+                   if !n.is_negative() {
+                       Some(numbervar(Integer::from(offset + &*n)))
+                   } else {
+                       None
+                   }
+               }
+               _ => {
+                   None
+               }
+            )
         }
-        Ok(Number::Integer(n)) if !n.is_negative() => Some(numbervar(Integer::from(offset + &*n))),
+        (HeapCellValueTag::Fixnum, n) => {
-        _ => None,
+            if n.get_num() >= 0 {
-    }
+                Some(numbervar(offset + Integer::from(n.get_num())))
+            } else {
+                None
+            }
+        }
+        _ => {
+            None
+        }
+    )
 }
 
 impl<'a, Outputter: HCValueOutputter> HCPrinter<'a, Outputter> {
     pub fn new(
         heap: &'a mut Heap,
-        atom_tbl: Arc<AtomTable>,
         stack: &'a mut Stack,
+        arena: &'a Arena,
         op_dir: &'a OpDir,
         output: Outputter,
-        cell: HeapCellValue,
+        term_loc: usize,
     ) -> Self {
         HCPrinter {
             outputter: output,
-            iter: stackful_preorder_iter(heap, stack, cell),
+            iter: stackful_preorder_iter(heap, stack, term_loc),
-            atom_tbl,
+            arena,
             op_dir,
             state_stack: vec![],
             toplevel_spec: None,
@@ -553,17 +589,6 @@ impl<'a, Outputter: HCValueOutputter> HCPrinter<'a, Outputter> {
         }
     }
 
-    #[inline]
-    fn ambiguity_check(&self, atom: &str) -> bool {
-        let tail = &self.outputter.as_str()[self.last_item_idx..];
-
-        if atom == "," || !self.quoted || non_quoted_token(atom.chars()) {
-            requires_space(tail, atom)
-        } else {
-            requires_space(tail, "'")
-        }
-    }
-
     fn set_parent_of_first_op(&mut self, parent_op: Option<DirectedOp>) {
         if let Some(op) = parent_op {
             if op.is_left() && op.is_prefix() {
@@ -806,13 +831,13 @@ impl<'a, Outputter: HCValueOutputter> HCPrinter<'a, Outputter> {
 
         read_heap_cell!(cell,
             (HeapCellValueTag::Lis | HeapCellValueTag::Str, h) => {
-                Some(format!("{}", h))
+                Some(format!("{h}"))
             }
             (HeapCellValueTag::Var | HeapCellValueTag::AttrVar, h) => {
-                Some(format!("_{}", h))
+                Some(format!("_{h}"))
             }
             (HeapCellValueTag::StackVar, h) => {
-                Some(format!("_s_{}", h))
+                Some(format!("_s_{h}"))
             }
             _ => {
                 None
@@ -878,7 +903,12 @@ impl<'a, Outputter: HCValueOutputter> HCPrinter<'a, Outputter> {
                                     } else {
                                         debug_assert!(cell.is_ref());
 
-                                        let h = cell.get_value() as usize;
+                                        let h = if cell.get_tag() == HeapCellValueTag::PStrLoc {
+                                            self.iter.focus().value()
+                                        } else {
+                                            cell.get_value()
+                                        } as usize;
+
                                         self.iter.push_stack(IterStackLoc::iterable_loc(
                                             h,
                                             HeapOrStackTag::Heap,
@@ -908,7 +938,7 @@ impl<'a, Outputter: HCValueOutputter> HCPrinter<'a, Outputter> {
                                             orig_cell = cell;
                                             continue;
                                         }
-                                    }
+                                    };
                                 }
                             }
 
@@ -972,13 +1002,13 @@ impl<'a, Outputter: HCValueOutputter> HCPrinter<'a, Outputter> {
     #[inline]
     fn print_ip_addr(&mut self, ip: IpAddr) {
         push_char!(self, '\'');
-        append_str!(self, &format!("{}", ip));
+        append_str!(self, &format!("{ip}"));
         push_char!(self, '\'');
     }
 
     #[inline]
     fn print_raw_ptr(&mut self, ptr: *const ArenaHeader) {
-        append_str!(self, &format!("0x{:x}", ptr as *const u8 as usize));
+        append_str!(self, &format!("0x{:x}", ptr.addr()));
     }
 
     fn print_number(&mut self, max_depth: usize, n: NumberFocus, op: &Option<DirectedOp>) {
@@ -1009,7 +1039,7 @@ impl<'a, Outputter: HCValueOutputter> HCPrinter<'a, Outputter> {
                     self.print_rational(max_depth, r, *op);
                 }
                 n => {
-                    let output_str = format!("{}", n);
+                    let output_str = format!("{n}");
 
                     push_space_if_amb!(self, &output_str, {
                         append_str!(self, &output_str);
@@ -1056,7 +1086,7 @@ impl<'a, Outputter: HCValueOutputter> HCPrinter<'a, Outputter> {
         match self.op_dir.get(&(atom!("rdiv"), Fixity::In)) {
             Some(op_desc) => {
                 if r.is_int() {
-                    let output_str = format!("{}", r);
+                    let output_str = format!("{r}");
 
                     push_space_if_amb!(self, &output_str, {
                         append_str!(self, &output_str);
@@ -1123,9 +1153,10 @@ impl<'a, Outputter: HCValueOutputter> HCPrinter<'a, Outputter> {
 
     // returns true if max_depth limit is reached and ellipsis is printed.
     fn print_string_as_functor(&mut self, focus: usize, max_depth: &mut usize) -> bool {
-        let iter = HeapPStrIter::new(self.iter.heap, focus);
+        let mut iter = HeapPStrIter::new(self.iter.heap, focus);
+        let mut char_count = 0;
 
-        for (char_count, c) in iter.chars().enumerate() {
+        while let Some(iteratee) = iter.next() {
             if self.check_max_depth(max_depth) {
                 if char_count > 0 {
                     self.state_stack.push(TokenOrRedirect::Close);
@@ -1135,13 +1166,34 @@ impl<'a, Outputter: HCValueOutputter> HCPrinter<'a, Outputter> {
                 return true;
             }
 
-            append_str!(self, "'.'");
+            macro_rules! emit_char {
-            push_char!(self, '(');
+                ($c:expr) => {{
+                    append_str!(self, "'.'");
+                    push_char!(self, '(');
 
-            print_char!(self, self.quoted, c);
+                    print_char!(self, self.quoted, $c);
-            push_char!(self, ',');
+                    push_char!(self, ',');
 
-            self.state_stack.push(TokenOrRedirect::Close);
+                    self.state_stack.push(TokenOrRedirect::Close);
+                    char_count += 1;
+                }};
+            }
+
+            match iteratee {
+                PStrIteratee::Char { value, .. } => {
+                    emit_char!(value);
+                }
+                PStrIteratee::PStrSlice {
+                    slice_loc,
+                    slice_len,
+                } => {
+                    let s = iter.heap.slice_to_str(slice_loc, slice_len);
+
+                    for c in s.chars() {
+                        emit_char!(c);
+                    }
+                }
+            }
         }
 
         false
@@ -1152,7 +1204,8 @@ impl<'a, Outputter: HCValueOutputter> HCPrinter<'a, Outputter> {
     fn print_proper_string(&mut self, focus: usize, max_depth: usize) {
         push_char!(self, '"');
 
-        let iter = HeapPStrIter::new(self.iter.heap, focus);
+        let mut iter = HeapPStrIter::new(self.iter.heap, focus);
+
         let char_to_string = |c: char| {
             // refrain from quoting characters other than '"' and '\'
             // unless self.quoted is true.
@@ -1164,19 +1217,45 @@ impl<'a, Outputter: HCValueOutputter> HCPrinter<'a, Outputter> {
         };
 
         if max_depth == 0 {
-            for c in iter.chars() {
+            while let Some(iteratee) = iter.next() {
-                for c in char_to_string(c).chars() {
+                let iter: Box<dyn Iterator<Item = char>> = match iteratee {
-                    push_char!(self, c);
+                    PStrIteratee::Char { value: c, .. } => Box::new(std::iter::once(c)),
+                    PStrIteratee::PStrSlice {
+                        slice_loc,
+                        slice_len,
+                    } => {
+                        let s = iter.heap.slice_to_str(slice_loc, slice_len);
+                        Box::new(s.chars())
+                    }
+                };
+
+                for c in iter {
+                    for c in char_to_string(c).chars() {
+                        push_char!(self, c);
+                    }
                 }
             }
         } else {
             let mut char_count = 0;
 
-            for c in iter.chars().take(max_depth) {
+            while let Some(iteratee) = iter.next() {
-                char_count += 1;
+                let iter: Box<dyn Iterator<Item = char>> = match iteratee {
+                    PStrIteratee::Char { value: c, .. } => Box::new(std::iter::once(c)),
+                    PStrIteratee::PStrSlice {
+                        slice_loc,
+                        slice_len,
+                    } => {
+                        let s = iter.heap.slice_to_str(slice_loc, slice_len);
+                        Box::new(s.chars())
+                    }
+                };
 
-                for c in char_to_string(c).chars() {
+                for c in iter.take(max_depth - char_count) {
-                    push_char!(self, c);
+                    char_count += 1;
+
+                    for c in char_to_string(c).chars() {
+                        push_char!(self, c);
+                    }
                 }
             }
 
@@ -1194,10 +1273,9 @@ impl<'a, Outputter: HCValueOutputter> HCPrinter<'a, Outputter> {
                 self.iter.pop_stack();
                 self.iter.pop_stack();
             }
-            HeapCellValueTag::PStr | HeapCellValueTag::PStrOffset => {
+            HeapCellValueTag::PStrLoc => {
                 self.iter.pop_stack();
             }
-            HeapCellValueTag::CStr => {}
             _ => {
                 unreachable!();
             }
@@ -1208,19 +1286,15 @@ impl<'a, Outputter: HCValueOutputter> HCPrinter<'a, Outputter> {
         let focus = self.iter.focus();
         let mut heap_pstr_iter = HeapPStrIter::new(self.iter.heap, focus.value() as usize);
 
-        let next_h;
+        let is_cyclic = if heap_pstr_iter.next().is_some() {
-        let next_hare;
-
-        if heap_pstr_iter.next().is_some() {
-            next_h = heap_pstr_iter.focus;
-            next_hare = heap_pstr_iter.focus();
             for _ in heap_pstr_iter.by_ref() {}
+            heap_pstr_iter.is_cyclic()
         } else {
             return self.push_list(max_depth);
-        }
+        };
 
         let end_h = heap_pstr_iter.focus();
-        let end_cell = heap_pstr_iter.focus;
+        let end_cell = heap_pstr_iter.heap[end_h]; // heap_pstr_iter.focus;
 
         if self.check_max_depth(&mut max_depth) {
             self.remove_list_children(focus.value() as usize);
@@ -1230,7 +1304,11 @@ impl<'a, Outputter: HCValueOutputter> HCPrinter<'a, Outputter> {
 
         let at_cdr = self.outputter.ends_with("|");
 
-        if self.double_quotes && !self.ignore_ops && end_cell.is_string_terminator(self.iter.heap) {
+        if self.double_quotes
+            && !self.ignore_ops
+            && !is_cyclic
+            && end_cell.is_string_terminator(self.iter.heap)
+        {
             self.remove_list_children(focus.value() as usize);
             return self.print_proper_string(focus.value() as usize, max_depth);
         }
@@ -1261,37 +1339,27 @@ impl<'a, Outputter: HCValueOutputter> HCPrinter<'a, Outputter> {
                 (HeapCellValueTag::Lis) => {
                     self.push_list(max_depth)
                 }
-                _ => {
+                (HeapCellValueTag::PStrLoc, h) => {
                     let switch = Rc::new(Cell::new((!at_cdr, 0)));
                     let switch = self.close_list(switch);
 
-                    let (h, offset) = pstr_loc_and_offset(self.iter.heap, focus.value() as usize);
-
-                    let offset = offset.get_num() as usize;
-                    let tag = value.get_tag();
-
-                    let end_h = if tag == HeapCellValueTag::PStrOffset {
-                        // remove the fixnum offset from the iterator stack so we don't
-                        // print an extraneous number. pstr offset value cells are never
-                        // used by the iterator to mark cyclic terms so the removal is safe.
-                        self.iter.pop_stack();
-                        Some(next_hare)
-                        // Some(end_h)
-                    } else {
-                        None
-                    };
-
                     if !self.max_depth_exhausted(max_depth) {
-                        let pstr = cell_as_string!(self.iter.heap[h]);
+                        self.state_stack.push(
-                        self.state_stack.push(TokenOrRedirect::CommaSeparatedCharList(CommaSeparatedCharList {
+                            TokenOrRedirect::CommaSeparatedCharList(
-                            pstr, offset, max_depth, end_cell: next_h, end_h,
+                                CommaSeparatedCharList {
-                        }));
+                                    pstr_loc: h, max_depth,
+                                }
+                            ),
+                        );
                     } else {
                         self.state_stack.push(TokenOrRedirect::Atom(atom!("...")));
                     }
 
                     self.open_list(switch);
                 }
+                _ => {
+                    unreachable!()
+                }
             );
         }
     }
@@ -1384,7 +1452,7 @@ impl<'a, Outputter: HCValueOutputter> HCPrinter<'a, Outputter> {
                 || if let Some(ref op) = op {
                     if self.numbervars && arity == 1 && name == atom!("$VAR") {
                         !self.iter.immediate_leaf_has_property(|addr| {
-                            match Number::try_from(addr) {
+                            match Number::try_from((addr, &self.arena.f64_tbl)) {
                                 Ok(Number::Integer(n)) => (*n).sign() == Sign::Positive,
                                 Ok(Number::Fixnum(n)) => n.get_num() >= 0,
                                 Ok(Number::Float(f)) => f >= OrderedFloat(0f64),
@@ -1458,7 +1526,7 @@ impl<'a, Outputter: HCValueOutputter> HCPrinter<'a, Outputter> {
 
             self.state_stack.push(TokenOrRedirect::NumberFocus(
                 max_depth,
-                NumberFocus::Unfocused(Number::Fixnum(Fixnum::build_with(port as i64))),
+                NumberFocus::Unfocused(Number::Fixnum(Fixnum::build_with(port))),
                 None,
             ));
             self.state_stack.push(TokenOrRedirect::Comma);
@@ -1469,23 +1537,29 @@ impl<'a, Outputter: HCValueOutputter> HCPrinter<'a, Outputter> {
         }
     }
 
-    fn print_index_ptr(&mut self, index_ptr: IndexPtr, max_depth: usize) {
+    fn print_index_ptr(&mut self, idx: CodeIndexOffset, max_depth: usize) {
         if self.format_struct(max_depth, 1, atom!("$index_ptr")) {
             let atom = self.state_stack.pop().unwrap();
 
             self.state_stack.pop();
             self.state_stack.pop();
 
-            let offset = if index_ptr.is_undefined() || index_ptr.is_dynamic_undefined() {
+            let idx_ptr = self.arena.code_index_tbl.get_entry(idx);
+
+            let offset = if idx_ptr.is_undefined() || idx_ptr.is_dynamic_undefined() {
                 TokenOrRedirect::Atom(atom!("undefined"))
             } else {
-                let idx = index_ptr.p() as i64;
+                let idx_ptr_p = idx_ptr.p() as i64;
 
-                TokenOrRedirect::NumberFocus(
+                if let Ok(n) = Fixnum::build_with_checked(idx_ptr_p) {
-                    max_depth,
+                    TokenOrRedirect::NumberFocus(
-                    NumberFocus::Unfocused(Number::Fixnum(Fixnum::build_with(idx))),
+                        max_depth,
-                    None,
+                        NumberFocus::Unfocused(Number::Fixnum(n)),
-                )
+                        None,
+                    )
+                } else {
+                    TokenOrRedirect::Atom(atom!("out_of_bounds_idx_ptr"))
+                }
             };
 
             self.state_stack.push(offset);
@@ -1521,32 +1595,26 @@ impl<'a, Outputter: HCValueOutputter> HCPrinter<'a, Outputter> {
 
     fn print_comma_separated_char_list(&mut self, char_list: CommaSeparatedCharList) {
         let CommaSeparatedCharList {
-            pstr,
+            pstr_loc,
-            offset,
             max_depth,
-            end_cell,
-            end_h,
         } = char_list;
-        let pstr_str = pstr.as_str_from(offset);
 
-        if let Some(c) = pstr_str.chars().next() {
+        let c = self.iter.heap.char_at(pstr_loc);
-            let offset = offset + c.len_utf8();
 
+        if c != '\u{0}' {
             if !self.max_depth_exhausted(max_depth) {
                 self.state_stack
                     .push(TokenOrRedirect::CommaSeparatedCharList(
                         CommaSeparatedCharList {
-                            pstr,
+                            pstr_loc: pstr_loc + c.len_utf8(),
-                            offset,
                             max_depth: max_depth.saturating_sub(1),
-                            end_cell,
-                            end_h,
                         },
                     ));
 
                 let max_depth_allows = self.max_depth == 0 || max_depth > 1;
+                let next_c = self.iter.heap.char_at(pstr_loc + c.len_utf8());
 
-                if max_depth_allows && pstr_str.chars().nth(1).is_some() {
+                if max_depth_allows && next_c != '\u{0}' {
                     self.state_stack.push(TokenOrRedirect::Comma);
                 }
 
@@ -1558,12 +1626,7 @@ impl<'a, Outputter: HCValueOutputter> HCPrinter<'a, Outputter> {
         } else if self.max_depth_exhausted(max_depth) {
             self.state_stack.push(TokenOrRedirect::Atom(atom!("...")));
             self.state_stack.push(TokenOrRedirect::HeadTailSeparator);
-        } else if end_cell != empty_list_as_cell!() {
+        } else {
-            if let Some(end_h) = end_h {
-                self.iter
-                    .push_stack(IterStackLoc::iterable_loc(end_h, HeapOrStackTag::Heap));
-            }
-
             self.state_stack
                 .push(TokenOrRedirect::FunctorRedirect(max_depth + 1));
             self.state_stack.push(TokenOrRedirect::HeadTailSeparator);
@@ -1576,7 +1639,8 @@ impl<'a, Outputter: HCValueOutputter> HCPrinter<'a, Outputter> {
         is_functor_redirect: bool,
         mut max_depth: usize,
     ) {
-        let negated_operand = negated_op_needs_bracketing(&self.iter, self.op_dir, &op);
+        let negated_operand =
+            negated_op_needs_bracketing(&self.iter, &self.arena.f64_tbl, self.op_dir, &op);
 
         let addr = match self.check_for_seen(&mut max_depth) {
             Some(addr) => addr,
@@ -1658,10 +1722,6 @@ impl<'a, Outputter: HCValueOutputter> HCPrinter<'a, Outputter> {
             (HeapCellValueTag::Atom, (name, arity)) => {
                 print_struct(self, name, arity);
             }
-            (HeapCellValueTag::Char, c) => {
-                let name = AtomTable::build_with(&self.atom_tbl, &String::from(c));
-                print_struct(self, name, 0);
-            }
             (HeapCellValueTag::Str, s) => {
                 let (name, arity) = cell_as_atom_cell!(self.iter.heap[s])
                     .get_name_and_arity();
@@ -1682,13 +1742,17 @@ impl<'a, Outputter: HCValueOutputter> HCPrinter<'a, Outputter> {
                     });
                 }
             }
+            (HeapCellValueTag::CodeIndexOffset, idx) => {
+                self.print_index_ptr(idx, self.max_depth);
+            }
             (HeapCellValueTag::Fixnum | HeapCellValueTag::CutPoint, n) => {
                 self.print_number(max_depth, NumberFocus::Unfocused(Number::Fixnum(n)), &op);
             }
-            (HeapCellValueTag::F64, f) => {
+            (HeapCellValueTag::F64Offset, offset) => {
-                self.print_number(max_depth, NumberFocus::Unfocused(Number::Float(*f)), &op);
+                let f = self.arena.f64_tbl.get_entry(offset);
+                self.print_number(max_depth, NumberFocus::Unfocused(Number::Float(f)), &op);
             }
-            (HeapCellValueTag::CStr | HeapCellValueTag::PStr | HeapCellValueTag::PStrOffset) => {
+            (HeapCellValueTag::PStrLoc) => {
                 self.print_list_like(max_depth);
             }
             (HeapCellValueTag::Lis) => {
@@ -1725,8 +1789,22 @@ impl<'a, Outputter: HCValueOutputter> HCPrinter<'a, Outputter> {
                    (ArenaHeaderTag::Dropped, _value) => {
                        self.print_impromptu_atom(atom!("$dropped_value"));
                    }
-                   (ArenaHeaderTag::IndexPtr, index_ptr) => {
+                   (ArenaHeaderTag::ChildProcess, process) => {
-                       self.print_index_ptr(*index_ptr, max_depth);
+
+                        let process_atom = atom!("$process");
+
+                        if self.format_struct(max_depth, 1, process_atom) {
+                            let atom = TokenOrRedirect::NumberFocus(max_depth, NumberFocus::Unfocused(Number::Fixnum(Fixnum::build_with(process.id()))), op);
+
+                            let process_root = self.state_stack.pop().unwrap();
+
+                            self.state_stack.pop();
+                            self.state_stack.pop();
+
+                            self.state_stack.push(atom);
+                            self.state_stack.push(TokenOrRedirect::Open);
+                            self.state_stack.push(process_root);
+                        }
                    }
                    _ => {
                    }
@@ -1825,6 +1903,7 @@ impl<'a, Outputter: HCValueOutputter> HCPrinter<'a, Outputter> {
 mod tests {
     use super::*;
 
+    use crate::functor_macro::*;
     use crate::machine::mock_wam::*;
 
     #[test]
@@ -1832,23 +1911,30 @@ mod tests {
     fn term_printing_tests() {
         let mut wam = MockWAM::new();
 
+        // clear the heap of resource error data etc
+        wam.machine_st.heap.clear();
+
         let f_atom = atom!("f");
         let a_atom = atom!("a");
         let b_atom = atom!("b");
         let c_atom = atom!("c");
 
-        wam.machine_st
+        let mut functor_writer = Heap::functor_writer(functor!(
-            .heap
+            f_atom,
-            .extend(functor!(f_atom, [atom(a_atom), atom(b_atom)]));
+            [atom_as_cell(a_atom), atom_as_cell(b_atom)]
+        ));
+
+        let cell = functor_writer(&mut wam.machine_st.heap).unwrap();
+        wam.machine_st.heap.push_cell(cell).unwrap();
 
         {
             let printer = HCPrinter::new(
                 &mut wam.machine_st.heap,
-                Arc::clone(&wam.machine_st.atom_tbl),
                 &mut wam.machine_st.stack,
+                &wam.machine_st.arena,
                 &wam.op_dir,
                 PrinterOutputter::new(),
-                heap_loc_as_cell!(0),
+                3,
             );
 
             let output = printer.print();
@@ -1860,24 +1946,28 @@ mod tests {
 
         wam.machine_st.heap.clear();
 
-        wam.machine_st.heap.extend(functor!(
+        let mut functor_writer = Heap::functor_writer(functor!(
             f_atom,
             [
-                atom(a_atom),
+                atom_as_cell(a_atom),
-                atom(b_atom),
+                atom_as_cell(b_atom),
-                atom(a_atom),
+                atom_as_cell(a_atom),
-                cell(str_loc_as_cell!(0))
+                str_loc_as_cell(0)
             ]
         ));
 
+        let cell = functor_writer(&mut wam.machine_st.heap).unwrap();
+
+        wam.machine_st.heap.push_cell(cell).unwrap();
+
         {
             let printer = HCPrinter::new(
                 &mut wam.machine_st.heap,
-                Arc::clone(&wam.machine_st.atom_tbl),
                 &mut wam.machine_st.stack,
+                &wam.machine_st.arena,
                 &wam.op_dir,
                 PrinterOutputter::new(),
-                heap_loc_as_cell!(0),
+                5,
             );
 
             let output = printer.print();
@@ -1889,19 +1979,23 @@ mod tests {
 
         wam.machine_st.heap.clear();
 
+        let mut writer = wam.machine_st.heap.reserve(96).unwrap();
+
         // print L = [L|L].
-        wam.machine_st.heap.push(list_loc_as_cell!(1));
+        writer.write_with(|section| {
-        wam.machine_st.heap.push(list_loc_as_cell!(1));
+            section.push_cell(list_loc_as_cell!(1));
-        wam.machine_st.heap.push(list_loc_as_cell!(1));
+            section.push_cell(list_loc_as_cell!(1));
+            section.push_cell(list_loc_as_cell!(1));
+        });
 
         {
             let printer = HCPrinter::new(
                 &mut wam.machine_st.heap,
-                Arc::clone(&wam.machine_st.atom_tbl),
                 &mut wam.machine_st.stack,
+                &wam.machine_st.arena,
                 &wam.op_dir,
                 PrinterOutputter::new(),
-                heap_loc_as_cell!(0),
+                0,
             );
 
             let output = printer.print();
@@ -1910,11 +2004,11 @@ mod tests {
 
             let mut printer = HCPrinter::new(
                 &mut wam.machine_st.heap,
-                Arc::clone(&wam.machine_st.atom_tbl),
                 &mut wam.machine_st.stack,
+                &wam.machine_st.arena,
                 &wam.op_dir,
                 PrinterOutputter::new(),
-                heap_loc_as_cell!(0),
+                0,
             );
 
             printer
@@ -1930,24 +2024,35 @@ mod tests {
 
         wam.machine_st.heap.clear();
 
-        let functor = functor!(f_atom, [atom(a_atom), atom(b_atom), atom(b_atom)]);
+        let mut writer = wam.machine_st.heap.reserve(96).unwrap();
 
-        wam.machine_st.heap.push(list_loc_as_cell!(1));
+        writer.write_with(|section| {
-        wam.machine_st.heap.push(str_loc_as_cell!(5));
+            section.push_cell(list_loc_as_cell!(1));
-        wam.machine_st.heap.push(list_loc_as_cell!(3));
+            section.push_cell(str_loc_as_cell!(5));
-        wam.machine_st.heap.push(str_loc_as_cell!(5));
+            section.push_cell(list_loc_as_cell!(3));
-        wam.machine_st.heap.push(empty_list_as_cell!());
+            section.push_cell(str_loc_as_cell!(5));
+            section.push_cell(empty_list_as_cell!());
+        });
 
-        wam.machine_st.heap.extend(functor);
+        let mut functor_writer = Heap::functor_writer(functor!(
+            f_atom,
+            [
+                atom_as_cell(a_atom),
+                atom_as_cell(b_atom),
+                atom_as_cell(b_atom)
+            ]
+        ));
+
+        functor_writer(&mut wam.machine_st.heap).unwrap();
 
         {
             let printer = HCPrinter::new(
                 &mut wam.machine_st.heap,
-                Arc::clone(&wam.machine_st.atom_tbl),
                 &mut wam.machine_st.stack,
+                &wam.machine_st.arena,
                 &wam.op_dir,
                 PrinterOutputter::new(),
-                heap_loc_as_cell!(0),
+                0,
             );
 
             let output = printer.print();
@@ -1962,11 +2067,11 @@ mod tests {
         {
             let printer = HCPrinter::new(
                 &mut wam.machine_st.heap,
-                Arc::clone(&wam.machine_st.atom_tbl),
                 &mut wam.machine_st.stack,
+                &wam.machine_st.arena,
                 &wam.op_dir,
                 PrinterOutputter::new(),
-                heap_loc_as_cell!(0),
+                0,
             );
 
             let output = printer.print();
@@ -1979,11 +2084,11 @@ mod tests {
         {
             let mut printer = HCPrinter::new(
                 &mut wam.machine_st.heap,
-                Arc::clone(&wam.machine_st.atom_tbl),
                 &mut wam.machine_st.stack,
+                &wam.machine_st.arena,
                 &wam.op_dir,
                 PrinterOutputter::new(),
-                heap_loc_as_cell!(0),
+                0,
             );
 
             printer
@@ -1999,23 +2104,28 @@ mod tests {
 
         // issue #382
         wam.machine_st.heap.clear();
-        wam.machine_st.heap.push(list_loc_as_cell!(1));
 
-        for idx in 0..3000 {
+        let mut writer = wam.machine_st.heap.reserve(6002).unwrap();
-            wam.machine_st.heap.push(heap_loc_as_cell!(2 * idx + 1));
-            wam.machine_st.heap.push(list_loc_as_cell!(2 * idx + 2 + 1));
-        }
 
-        wam.machine_st.heap.push(empty_list_as_cell!());
+        writer.write_with(|section| {
+            section.push_cell(list_loc_as_cell!(1));
+
+            for idx in 0..3000 {
+                section.push_cell(heap_loc_as_cell!(2 * idx + 1));
+                section.push_cell(list_loc_as_cell!(2 * idx + 2 + 1));
+            }
+
+            section.push_cell(empty_list_as_cell!());
+        });
 
         {
             let mut printer = HCPrinter::new(
                 &mut wam.machine_st.heap,
-                Arc::clone(&wam.machine_st.atom_tbl),
                 &mut wam.machine_st.stack,
+                &wam.machine_st.arena,
                 &wam.op_dir,
                 PrinterOutputter::new(),
-                heap_loc_as_cell!(0),
+                0,
             );
 
             printer.max_depth = 5;
@@ -2029,16 +2139,19 @@ mod tests {
 
         wam.machine_st.heap.clear();
 
-        put_partial_string(&mut wam.machine_st.heap, "abc", &wam.machine_st.atom_tbl);
+        wam.machine_st.heap.allocate_pstr("abc").unwrap();
+
+        wam.machine_st.heap.push_cell(heap_loc_as_cell!(1)).unwrap();
+        wam.machine_st.heap.push_cell(pstr_loc_as_cell!(0)).unwrap();
 
         {
             let printer = HCPrinter::new(
                 &mut wam.machine_st.heap,
-                Arc::clone(&wam.machine_st.atom_tbl),
                 &mut wam.machine_st.stack,
+                &wam.machine_st.arena,
                 &wam.op_dir,
                 PrinterOutputter::new(),
-                pstr_loc_as_cell!(0),
+                2,
             );
 
             let output = printer.print();
@@ -2048,25 +2161,27 @@ mod tests {
 
         all_cells_unmarked(&wam.machine_st.heap);
 
-        wam.machine_st.heap.pop();
+        let mut writer = wam.machine_st.heap.reserve(96).unwrap();
 
-        wam.machine_st.heap.push(list_loc_as_cell!(2));
+        writer.write_with(|section| {
+            section.push_cell(atom_as_cell!(a_atom));
+            section.push_cell(list_loc_as_cell!(5));
+            section.push_cell(atom_as_cell!(b_atom));
+            section.push_cell(list_loc_as_cell!(7));
+            section.push_cell(atom_as_cell!(c_atom));
+            section.push_cell(empty_list_as_cell!());
+        });
 
-        wam.machine_st.heap.push(atom_as_cell!(a_atom));
+        wam.machine_st.heap[1] = list_loc_as_cell!(3);
-        wam.machine_st.heap.push(list_loc_as_cell!(4));
-        wam.machine_st.heap.push(atom_as_cell!(b_atom));
-        wam.machine_st.heap.push(list_loc_as_cell!(6));
-        wam.machine_st.heap.push(atom_as_cell!(c_atom));
-        wam.machine_st.heap.push(empty_list_as_cell!());
 
         {
             let mut printer = HCPrinter::new(
                 &mut wam.machine_st.heap,
-                Arc::clone(&wam.machine_st.atom_tbl),
                 &mut wam.machine_st.stack,
+                &wam.machine_st.arena,
                 &wam.op_dir,
                 PrinterOutputter::new(),
-                heap_loc_as_cell!(0),
+                2,
             );
 
             printer.double_quotes = true;

src/indexing.rs

@@ -3,6 +3,7 @@ use crate::parser::ast::*;
 
 use crate::forms::*;
 use crate::instructions::*;
+use crate::types::HeapCellValue;
 
 use fxhash::FxBuildHasher;
 use indexmap::IndexMap;
@@ -112,7 +113,7 @@ impl<'a> IndexingCodeMergingPtr<'a> {
 
         match constant_key {
             Some(OptArgIndexKey::Literal(_, _, constant, _)) => {
-                constants.insert(*constant, constant_ptr);
+                constants.insert(HeapCellValue::from(*constant), constant_ptr);
             }
             _ if constant_ptr.is_external() => {
                 // this must be a defunct clause, because it's been deleted
@@ -144,7 +145,7 @@ impl<'a> IndexingCodeMergingPtr<'a> {
     fn add_static_indexed_choice_for_constant(
         &mut self,
         external: usize,
-        constant: Literal,
+        constant: HeapCellValue,
         index: usize,
     ) {
         let third_level_index = if self.append_or_prepend.is_append() {
@@ -181,7 +182,7 @@ impl<'a> IndexingCodeMergingPtr<'a> {
     fn add_dynamic_indexed_choice_for_constant(
         &mut self,
         external: usize,
-        constant: Literal,
+        constant: HeapCellValue,
         index: usize,
     ) {
         let third_level_index = if self.append_or_prepend.is_append() {
@@ -235,8 +236,8 @@ impl<'a> IndexingCodeMergingPtr<'a> {
 
     fn index_overlapping_constant(
         &mut self,
-        orig_constant: Literal,
+        orig_constant: HeapCellValue,
-        overlapping_constant: Literal,
+        overlapping_constant: HeapCellValue,
         index: usize,
     ) {
         loop {
@@ -316,7 +317,7 @@ impl<'a> IndexingCodeMergingPtr<'a> {
         }
     }
 
-    fn index_constant(&mut self, constant: Literal, index: usize) {
+    fn index_constant(&mut self, constant: HeapCellValue, index: usize) {
         loop {
             let indexing_code_len = self.indexing_code.len();
 
@@ -633,12 +634,15 @@ pub(crate) fn merge_clause_index(
     match &opt_arg_index_key {
         OptArgIndexKey::Literal(_, index_loc, constant, ref overlapping_constants) => {
             let offset = new_clause_loc - index_loc + 1;
-            merging_ptr.index_constant(*constant, offset);
+            merging_ptr.index_constant(HeapCellValue::from(*constant), offset);
 
-            for overlapping_constant in overlapping_constants {
+            if let Some(overlapping_constant) = overlapping_constants {
                 merging_ptr.offset = 0;
-
+                merging_ptr.index_overlapping_constant(
-                merging_ptr.index_overlapping_constant(*constant, *overlapping_constant, offset);
+                    HeapCellValue::from(*constant),
+                    HeapCellValue::from(*overlapping_constant),
+                    offset,
+                );
             }
         }
         OptArgIndexKey::Structure(_, index_loc, name, arity) => {
@@ -664,7 +668,7 @@ pub(crate) fn merge_clause_index(
 
 pub(crate) fn remove_constant_indices(
     constant: Literal,
-    overlapping_constants: &[Literal],
+    overlapping_constants: Option<Literal>,
     indexing_code: &mut [IndexingLine],
     offset: usize,
 ) {
@@ -693,7 +697,7 @@ pub(crate) fn remove_constant_indices(
 
     let mut constants_index = 0;
 
-    for constant in iter {
+    for constant in iter.map(|l| HeapCellValue::from(*l)) {
         loop {
             match &mut indexing_code[index] {
                 IndexingLine::Indexing(IndexingInstruction::SwitchOnConstant(
@@ -701,8 +705,6 @@ pub(crate) fn remove_constant_indices(
                 )) => {
                     constants_index = index;
 
-                    let constant = *constant;
-
                     match constants.get(&constant).cloned() {
                         Some(IndexingCodePtr::DynamicExternal(_))
                         | Some(IndexingCodePtr::External(_))
@@ -740,7 +742,7 @@ pub(crate) fn remove_constant_indices(
                                 IndexingLine::Indexing(IndexingInstruction::SwitchOnConstant(
                                     ref mut constants,
                                 )) => {
-                                    constants.insert(*constant, ext);
+                                    constants.insert(constant, ext);
                                 }
                                 _ => {
                                     unreachable!()
@@ -773,7 +775,7 @@ pub(crate) fn remove_constant_indices(
                                 IndexingLine::Indexing(IndexingInstruction::SwitchOnConstant(
                                     ref mut constants,
                                 )) => {
-                                    constants.insert(*constant, ext);
+                                    constants.insert(constant, ext);
                                 }
                                 _ => {
                                     unreachable!()
@@ -1033,7 +1035,7 @@ pub(crate) fn remove_index(
 ) {
     match opt_arg_index_key {
         OptArgIndexKey::Literal(_, _, constant, ref overlapping_constants) => {
-            remove_constant_indices(*constant, overlapping_constants, indexing_code, clause_loc);
+            remove_constant_indices(*constant, *overlapping_constants, indexing_code, clause_loc);
         }
         OptArgIndexKey::Structure(_, _, name, arity) => {
             remove_structure_index(*name, *arity, indexing_code, clause_loc);
@@ -1095,56 +1097,26 @@ fn uncap_choice_seq_with_try(prelude: &mut [IndexedChoiceInstruction]) {
     }
 }
 
-pub(crate) fn constant_key_alternatives(
+pub(crate) fn constant_key_alternatives(constant: Literal) -> Option<Literal> {
-    constant: Literal,
+    let n = match &constant {
-    atom_tbl: &AtomTable,
+        Literal::Rational(n) if n.denominator().is_one() => n.numerator(),
-    // arena: &mut Arena,
+        Literal::Integer(n) => n,
-) -> Vec<Literal> {
+        _ => return None,
-    let mut constants = vec![];
+    };
 
-    match constant {
+    Fixnum::build_with_checked(n).map(Literal::Fixnum).ok()
-        Literal::Atom(ref name) => {
-            if let Some(c) = name.as_char() {
-                constants.push(Literal::Char(c));
-            }
-        }
-        Literal::Char(c) => {
-            let atom = AtomTable::build_with(atom_tbl, &c.to_string());
-            constants.push(Literal::Atom(atom));
-        }
-        /*
-        // constant_to_literal takes care of the downward conversion from Integer to Fixnum
-        // if possible.
-        Literal::Fixnum(ref n) => {
-            constants.push(Literal::Integer(arena_alloc!(n, arena)));
-        }
-        */
-        Literal::Integer(ref n) => {
-            let result = (&**n).try_into();
-            if let Ok(value) = result {
-                Fixnum::build_with_checked(value)
-                    .map(|n| {
-                        constants.push(Literal::Fixnum(n));
-                    })
-                    .unwrap();
-            }
-        }
-        _ => {}
-    }
-
-    constants
 }
 
 #[derive(Debug)]
 pub(crate) struct StaticCodeIndices {
-    constants: IndexMap<Literal, VecDeque<IndexedChoiceInstruction>, FxBuildHasher>,
+    constants: IndexMap<HeapCellValue, VecDeque<IndexedChoiceInstruction>, FxBuildHasher>,
     lists: VecDeque<IndexedChoiceInstruction>,
     structures: IndexMap<(Atom, usize), VecDeque<IndexedChoiceInstruction>, FxBuildHasher>,
 }
 
 #[derive(Debug)]
 pub(crate) struct DynamicCodeIndices {
-    constants: IndexMap<Literal, VecDeque<usize>, FxBuildHasher>,
+    constants: IndexMap<HeapCellValue, VecDeque<usize>, FxBuildHasher>,
     lists: VecDeque<usize>,
     structures: IndexMap<(Atom, usize), VecDeque<usize>, FxBuildHasher>,
 }
@@ -1156,7 +1128,7 @@ pub(crate) trait Indexer {
 
     fn constants(
         &mut self,
-    ) -> &mut IndexMap<Literal, VecDeque<Self::ThirdLevelIndex>, FxBuildHasher>;
+    ) -> &mut IndexMap<HeapCellValue, VecDeque<Self::ThirdLevelIndex>, FxBuildHasher>;
     fn lists(&mut self) -> &mut VecDeque<Self::ThirdLevelIndex>;
     fn structures(
         &mut self,
@@ -1204,7 +1176,7 @@ impl Indexer for StaticCodeIndices {
     #[inline]
     fn constants(
         &mut self,
-    ) -> &mut IndexMap<Literal, VecDeque<IndexedChoiceInstruction>, FxBuildHasher> {
+    ) -> &mut IndexMap<HeapCellValue, VecDeque<IndexedChoiceInstruction>, FxBuildHasher> {
         &mut self.constants
     }
 
@@ -1328,7 +1300,7 @@ impl Indexer for DynamicCodeIndices {
     }
 
     #[inline]
-    fn constants(&mut self) -> &mut IndexMap<Literal, VecDeque<usize>, FxBuildHasher> {
+    fn constants(&mut self) -> &mut IndexMap<HeapCellValue, VecDeque<usize>, FxBuildHasher> {
         &mut self.constants
     }
 
@@ -1447,14 +1419,13 @@ impl<I: Indexer> CodeOffsets<I> {
         self.indices.lists().push_back(index);
     }
 
-    fn index_constant(
+    fn index_constant(&mut self, constant: Literal, index: usize) -> Option<Literal> {
-        &mut self,
+        let overlapping_constant_opt = constant_key_alternatives(constant);
-        atom_tbl: &AtomTable,
+        let code = self
-        constant: Literal,
+            .indices
-        index: usize,
+            .constants()
-    ) -> Vec<Literal> {
+            .entry(HeapCellValue::from(constant))
-        let overlapping_constants = constant_key_alternatives(constant, atom_tbl);
+            .or_default();
-        let code = self.indices.constants().entry(constant).or_default();
 
         let is_initial_index = code.is_empty();
         code.push_back(I::compute_index(
@@ -1463,8 +1434,8 @@ impl<I: Indexer> CodeOffsets<I> {
             self.non_counted_bt,
         ));
 
-        for constant in &overlapping_constants {
+        if let Some(constant) = overlapping_constant_opt.map(HeapCellValue::from) {
-            let code = self.indices.constants().entry(*constant).or_default();
+            let code = self.indices.constants().entry(constant).or_default();
 
             let is_initial_index = code.is_empty();
             let index = I::compute_index(is_initial_index, index, self.non_counted_bt);
@@ -1472,7 +1443,7 @@ impl<I: Indexer> CodeOffsets<I> {
             code.push_back(index);
         }
 
-        overlapping_constants
+        overlapping_constant_opt
     }
 
     fn index_structure(&mut self, name: Atom, arity: usize, index: usize) -> usize {
@@ -1494,14 +1465,13 @@ impl<I: Indexer> CodeOffsets<I> {
         optimal_arg: &Term,
         index: usize,
         clause_index_info: &mut ClauseIndexInfo,
-        atom_tbl: &AtomTable,
     ) {
         match optimal_arg {
             &Term::Clause(_, atom!("."), ref terms) if terms.len() == 2 => {
                 clause_index_info.opt_arg_index_key = OptArgIndexKey::List(self.optimal_index, 0);
                 self.index_list(index);
             }
-            &Term::Cons(..) | &Term::Literal(_, Literal::String(_)) | &Term::PartialString(..) => {
+            &Term::Cons(..) | &Term::PartialString(..) | &Term::CompleteString(..) => {
                 clause_index_info.opt_arg_index_key = OptArgIndexKey::List(self.optimal_index, 0);
                 self.index_list(index);
             }
@@ -1512,7 +1482,7 @@ impl<I: Indexer> CodeOffsets<I> {
                 self.index_structure(name, terms.len(), index);
             }
             &Term::Literal(_, constant) => {
-                let overlapping_constants = self.index_constant(atom_tbl, constant, index);
+                let overlapping_constants = self.index_constant(constant, index);
 
                 clause_index_info.opt_arg_index_key =
                     OptArgIndexKey::Literal(self.optimal_index, 0, constant, overlapping_constants);

src/iterators.rs

@@ -6,6 +6,7 @@ use crate::parser::ast::*;
 use std::cell::Cell;
 use std::collections::VecDeque;
 use std::iter::*;
+use std::rc::Rc;
 use std::vec::Vec;
 
 #[allow(clippy::borrowed_box)]
@@ -15,27 +16,11 @@ pub(crate) enum TermRef<'a> {
     Cons(Level, &'a Cell<RegType>, &'a Term, &'a Term),
     Literal(Level, &'a Cell<RegType>, &'a Literal),
     Clause(Level, &'a Cell<RegType>, Atom, &'a Vec<Term>),
-    PartialString(Level, &'a Cell<RegType>, &'a String, &'a Box<Term>),
+    PartialString(Level, &'a Cell<RegType>, Rc<String>, &'a Box<Term>),
-    CompleteString(Level, &'a Cell<RegType>, Atom),
+    CompleteString(Level, &'a Cell<RegType>, Rc<String>),
     Var(Level, &'a Cell<VarReg>, VarPtr),
 }
 
-/*
-impl<'a> TermRef<'a> {
-    pub(crate) fn level(&self) -> Level {
-        match self {
-            TermRef::AnonVar(lvl) |
-            TermRef::Cons(lvl, ..) |
-            TermRef::Literal(lvl, ..) |
-            TermRef::Var(lvl, ..) |
-            TermRef::Clause(lvl, ..) |
-            TermRef::CompleteString(lvl, ..) |
-            TermRef::PartialString(lvl, ..) => *lvl,
-        }
-    }
-}
-*/
-
 #[allow(clippy::borrowed_box)]
 #[derive(Debug)]
 pub(crate) enum TermIterState<'a> {
@@ -44,9 +29,9 @@ pub(crate) enum TermIterState<'a> {
     Literal(Level, &'a Cell<RegType>, &'a Literal),
     InitialCons(Level, &'a Cell<RegType>, &'a Term, &'a Term),
     FinalCons(Level, &'a Cell<RegType>, &'a Term, &'a Term),
-    InitialPartialString(Level, &'a Cell<RegType>, &'a String, &'a Box<Term>),
+    InitialPartialString(Level, &'a Cell<RegType>, Rc<String>, &'a Box<Term>),
-    FinalPartialString(Level, &'a Cell<RegType>, &'a String, &'a Box<Term>),
+    FinalPartialString(Level, &'a Cell<RegType>, Rc<String>, &'a Box<Term>),
-    CompleteString(Level, &'a Cell<RegType>, Atom),
+    CompleteString(Level, &'a Cell<RegType>, Rc<String>),
     Var(Level, &'a Cell<VarReg>, VarPtr),
 }
 
@@ -62,9 +47,11 @@ impl<'a> TermIterState<'a> {
             }
             Term::Literal(cell, constant) => TermIterState::Literal(lvl, cell, constant),
             Term::PartialString(cell, string_buf, tail) => {
-                TermIterState::InitialPartialString(lvl, cell, string_buf, tail)
+                TermIterState::InitialPartialString(lvl, cell, string_buf.clone(), tail)
+            }
+            Term::CompleteString(cell, string) => {
+                TermIterState::CompleteString(lvl, cell, string.clone())
             }
-            Term::CompleteString(cell, atom) => TermIterState::CompleteString(lvl, cell, *atom),
             Term::Var(cell, var_ptr) => TermIterState::Var(lvl, cell, var_ptr.clone()),
         }
     }
@@ -182,11 +169,11 @@ impl<'a> Iterator for QueryIterator<'a> {
                         .push(TermIterState::FinalPartialString(lvl, cell, string, tail));
                     self.push_subterm(lvl.child_level(), tail);
                 }
-                TermIterState::FinalPartialString(lvl, cell, atom, tail) => {
+                TermIterState::FinalPartialString(lvl, cell, string, tail) => {
-                    return Some(TermRef::PartialString(lvl, cell, atom, tail));
+                    return Some(TermRef::PartialString(lvl, cell, string, tail));
                 }
-                TermIterState::CompleteString(lvl, cell, atom) => {
+                TermIterState::CompleteString(lvl, cell, string) => {
-                    return Some(TermRef::CompleteString(lvl, cell, atom));
+                    return Some(TermRef::CompleteString(lvl, cell, string));
                 }
                 TermIterState::FinalCons(lvl, cell, head, tail) => {
                     return Some(TermRef::Cons(lvl, cell, head, tail));
@@ -242,16 +229,20 @@ impl<'a> FactIterator<'a> {
                 head.as_ref(),
                 tail.as_ref(),
             )],
-            Term::PartialString(cell, string_buf, tail) => {
+            Term::PartialString(cell, string, tail) => {
                 vec![TermIterState::InitialPartialString(
                     Level::Root,
                     cell,
-                    string_buf,
+                    string.clone(),
                     tail,
                 )]
             }
-            Term::CompleteString(cell, atom) => {
+            Term::CompleteString(cell, string) => {
-                vec![TermIterState::CompleteString(Level::Root, cell, *atom)]
+                vec![TermIterState::CompleteString(
+                    Level::Root,
+                    cell,
+                    string.clone(),
+                )]
             }
             Term::Literal(cell, constant) => {
                 vec![TermIterState::Literal(Level::Root, cell, constant)]
@@ -336,7 +327,7 @@ pub(crate) enum ClauseItem<'a> {
     FirstBranch(usize),
     NextBranch,
     BranchEnd(usize),
-    Chunk(&'a VecDeque<QueryTerm>),
+    Chunk { terms: &'a VecDeque<QueryTerm> },
 }
 
 #[derive(Debug)]
@@ -412,8 +403,8 @@ impl<'a> Iterator for ClauseIterator<'a> {
                             self.state_stack
                                 .push(ClauseIteratorState::RemainingBranches(branches, 0));
                         }
-                        ChunkedTerms::Chunk(chunk) => {
+                        ChunkedTerms::Chunk { ref terms } => {
-                            return Some(ClauseItem::Chunk(chunk));
+                            return Some(ClauseItem::Chunk { terms });
                         }
                     }
                 }

src/lib.rs

@@ -11,8 +11,11 @@ pub(crate) mod macros;
 pub(crate) mod atom_table;
 #[macro_use]
 pub(crate) mod arena;
+pub(crate) mod offset_table;
 #[macro_use]
 pub(crate) mod parser;
+#[macro_use]
+pub(crate) mod functor_macro;
 mod allocator;
 mod arithmetic;
 pub(crate) mod codegen;

src/lib/builtins.pl

@@ -125,7 +125,7 @@ call(_, _, _, _, _, _, _, _, _).
 %
 % The flags that Scryer Prolog support are:
 %
-%  * `max_arity`: The max arity a predicate can have in Prolog. On Scryer is set to 1023. Read only.
+%  * `max_arity`: The max arity a predicate can have in Prolog. On Scryer is set to 255. Read only.
 %  * `bounded`: `true` if integer arithmethic is bounded between some min/max values. On Scryer is always set
 %    to `false` since it supports unbounded integer arithmethic. Read only.
 %  * `integer_rounding_function`: Describes the rounding donde by `//` and `rem` functions. On Scryer is
@@ -145,8 +145,8 @@ call(_, _, _, _, _, _, _, _, _).
 %    `fail` (the call silently fails) and `warn` (the call fails and a warning about the undefined predicate is printed).
 %  * `answer_write_options`: Additional write options used by the top level for writing answers.
 %
-current_prolog_flag(Flag, Value) :- Flag == max_arity, !, Value = 1023.
+current_prolog_flag(Flag, Value) :- Flag == max_arity, !, Value = 255.
-current_prolog_flag(max_arity, 1023).
+current_prolog_flag(max_arity, 255).
 current_prolog_flag(Flag, Value) :- Flag == bounded, !, Value = false.
 current_prolog_flag(bounded, false).
 current_prolog_flag(Flag, Value) :- Flag == integer_rounding_function, !, Value == toward_zero.
@@ -1719,20 +1719,27 @@ must_be_number(N, PI) :-
     ).
 
 
-chars_or_vars(Cs, _) :-
+chars_or_vars(Cs, PI) :-
+    (  '$is_partial_string'(Cs) ->
+       % use a fast test for the expected case
+       true
+    ;  chars_or_vars_(Cs, PI)
+    ).
+
+chars_or_vars_(Cs, _) :-
     (  var(Cs) ->
        !
     ;  Cs == [] ->
        !
     ).
-chars_or_vars([C|Cs], PI) :-
+chars_or_vars_([C|Cs], PI) :-
     (  nonvar(C) ->
        (  atom(C),
           atom_length(C, 1) ->
-          chars_or_vars(Cs, PI)
+          chars_or_vars_(Cs, PI)
        ;  throw(error(type_error(character, C), PI))
        )
-    ;  chars_or_vars(Cs, PI)
+    ;  chars_or_vars_(Cs, PI)
     ).
 
 

src/lib/iso_ext.pl

@@ -22,6 +22,7 @@ but they're not part of the ISO Prolog standard at the moment.
 		    copy_term/3]).
 
 :- use_module(library(error), [can_be/2,
+                               must_be/2,
                                domain_error/3,
                                instantiation_error/1,
                                type_error/3]).
@@ -275,17 +276,15 @@ call_with_inference_limit(_, _, R, Bb, B) :-
     ;  nonvar(R)
     ).
 
-%% partial_string(String, L, L0)
+%% partial_string(String, Ls0, Ls)
 %
 % Explicitly construct a partial string "manually". It can be used as an optimized append/3.
 % It's not recommended to use this predicate in application code.
-partial_string(String, L, L0) :-
+partial_string(String, Ls0, Ls) :-
+    must_be(chars, String),
     (  String == [] ->
-       L = L0
+       Ls0 = Ls
-    ;  catch(atom_chars(Atom, String),
+    ;  '$create_partial_string'(String, Ls0, Ls)
-             error(E, _),
-             throw(error(E, partial_string/3))),
-       '$create_partial_string'(Atom, L, L0)
     ).
 
 %% partial_string(+String)

src/lib/pio.pl

@@ -39,7 +39,8 @@
 %  represented as a list of characters.
 
 phrase_from_stream(GRBody, Stream) :-
-    stream_to_lazy_list(Stream, Ls),
+    stream_property(Stream, reposition(Reposition)),
+    stream_to_lazy_list(Reposition, Stream, Ls),
     phrase(GRBody, Ls).
 
 %% phrase_from_file(+GRBody, +File)
@@ -64,7 +65,7 @@ phrase_from_file(NT, File, Options) :-
         ;   Type = text
         ),
         setup_call_cleanup(
-            open(File, read, Stream, Options),
+            open(File, read, Stream, [reposition(true)|Options]),
             phrase_from_stream(NT, Stream),
             close(Stream)
         )
@@ -73,34 +74,41 @@ phrase_from_file(NT, File, Options) :-
 % How many chars to read from stream and buffer in each step
 chars_to_read(4096).
 
-stream_to_lazy_list(Stream, Ls) :-
+stream_to_lazy_list(Reposition, Stream, Ls) :-
-    get_stream_buffer_position(Stream, Pos),
+    get_stream_buffer_position(Reposition, Stream, Pos),
-    freeze(Ls, render_step(Stream, Pos, Ls)).
+    freeze(Ls, render_step(Reposition, Stream, Pos, Ls)).
 
-render_step(Stream, Pos, Ls) :-
+render_step(Reposition, Stream, Pos, Ls) :-
-    set_stream_buffer_position(Stream, Pos),
+    set_stream_buffer_position(Reposition, Stream, Pos),
-    (   buffer_at_end_of_stream(Stream) ->
+    (   buffer_at_end_of_stream(Reposition, Stream) ->
         Ls = []
     ;   chars_to_read(CharsToRead),
-        buffer_get_n_chars(Stream, CharsToRead, Chars),
+        buffer_get_n_chars(Reposition, Stream, CharsToRead, Chars),
         partial_string(Chars, Ls, Ls0),
-        stream_to_lazy_list(Stream, Ls0)
+        stream_to_lazy_list(Reposition, Stream, Ls0)
     ).
 
-buffer_at_end_of_stream(Stream) :-
+buffer_at_end_of_stream(true, Stream) :- at_end_of_stream(Stream).
+buffer_at_end_of_stream(false, Stream) :-
     stream_bufferids(Stream, _, BufferPosId, _),
     bb_get(BufferPosId, Pos),
     Pos = eof.
 
-get_stream_buffer_position(Stream, Pos) :-
+get_stream_buffer_position(true, Stream, Pos) :-
+    stream_property(Stream, position(Pos)).
+get_stream_buffer_position(false, Stream, Pos) :-
     stream_bufferids(Stream, _, BufferPosId, _),
     bb_get(BufferPosId, Pos).
 
-set_stream_buffer_position(Stream, Pos) :-
+set_stream_buffer_position(true, Stream, Pos) :-
+    set_stream_position(Stream, Pos).
+set_stream_buffer_position(false, Stream, Pos) :-
     stream_bufferids(Stream, _, BufferPosId, _),
     bb_put(BufferPosId, Pos).
 
-buffer_get_n_chars(Stream, N, Chars) :-
+buffer_get_n_chars(true, Stream, N, Chars) :-
+    get_n_chars(Stream, N, Chars).
+buffer_get_n_chars(false, Stream, N, Chars) :-
     stream_bufferids(Stream, BufferId, BufferPosId, BufferLenId),
     buffer_prepare_for_n(Stream, BufferId, BufferPosId, BufferLenId, N),
     bb_get(BufferId, Buffer),

src/lib/process.pl

@@ -0,0 +1,224 @@
+:- module(process, [
+    process_create/3, 
+    process_id/2,
+    process_release/1, 
+    process_wait/2, 
+    process_wait/3, 
+    process_kill/1
+]).
+
+:- use_module(library(error)).
+:- use_module(library(iso_ext)).
+:- use_module(library(lists), [member/2, maplist/2, maplist/3, append/2]).
+:- use_module(library(reif), [tfilter/3, memberd_t/3]).
+
+
+%% process_create(+Exe, +Args:list, +Options).
+%
+% Create a new process by executing the executable Exe and passing it the Arguments Args.
+%
+% Note: On windows please take note of [windows argument splitting](https://doc.rust-lang.org/std/process/index.html#windows-argument-splitting).
+% 
+% Options is a list consisting of the following options:
+%
+%  * `cwd(+Path)`           Set the processes working directory to `Path`
+%  * `process(-Process)`    `Process` will be assigned a process handle for the spawned process
+%  * `env(+List)`           Don't inherit environment variables and set the variables defined in `List`
+%  * `environment(+List)`   Inherit environment variables and set/override the variables defined in `List`
+%  * `stdin(Spec)`, `stdout(Spec)` or `stderr(Spec)` defines how to redirect the spawned processes io streams
+%
+%  The elements of `List` in `env(List)`/`environment(List)` List must be string pairs using `=/2`.
+%  `env/1` and `environment/1` may not be both specified.
+%
+%  The following stdio `Spec` are available:
+%  
+%  * `std`          inherit the current processes original stdio streams (does currently not account for stdio being changed by `set_input` or `set_output`)
+%  * `file(+Path)`  attach the strea to the file at `Path`
+%  * `null`         discards writes and behaves as eof for read. Equivalent to using `file(/dev/null)`
+%  * `pipe(-Steam)` create a new pipe and assigne one end to the created process and the other end to `Stream`
+%
+% Specifying an option multiple times is an error, when an option is not specified the following defaults apply:
+%
+% - `cwd(".")`
+% - `environment([])`
+% - `stdin(std)`, `stdout(std)`, `stderr(std)`
+%
+process_create(Exe, Args, Options) :- call_with_error_context(process_create_(Exe, Args, Options), predicate-process_create/3).
+
+process_create_(Exe, Args, Options) :-
+    must_be(chars, Exe),
+    must_be(list, Args),
+    maplist(must_be(chars), Args),
+    must_be(list, Options),
+    check_options(
+        [
+            option([stdin], valid_stdio, stdin(std), stdin(Stdin)),
+            option([stdout], valid_stdio, stdout(std), stdout(Stdout)),
+            option([stderr], valid_stdio, stderr(std), stderr(Stderr)),
+            option([env, environment], valid_env, environment([]), Env),
+            option([process], valid_uninit_process, process(_), process(Process)),
+            option([cwd], valid_cwd, cwd("."), cwd(Cwd))
+        ],
+        Options,
+        process_create_option
+    ),
+    Stdin =.. Stdin1,
+    Stdout =.. Stdout1,
+    Stderr =.. Stderr1,
+    simplify_env(Env, Env1),
+    '$process_create'(Exe, Args, Stdin1, Stdout1, Stderr1, Env1, Cwd, Process).
+
+%% process_id(+Process, -Pid).
+%
+process_id(Process, Pid) :- call_with_error_context(process_id_(Process, Pid), predicate-process_id/2).
+
+process_id_(Process, Pid) :-
+    valid_process(Process),
+    must_be(var, Pid),
+    '$process_id'(Process, Pid).
+
+%% process_wait(+Process, Status).
+%
+% See `process_create/3` with `Options = []`
+%
+process_wait(Process, Status) :- call_with_error_context(process_wait(Process, Status, []), predicate-process_wait/2).
+
+
+%% process_wait(+Process, Status, Options).
+%
+% Wait for the process behind the process handle `Process` to exit.
+%
+% When the process exits regulary `Status` will be unified with `exit(Exit)` where `Exit` is the processes exit code.
+% When the process exits was killed `Status` will be unified with `killed(Signal)` where `Signal` is the signal number that killed the process.
+% When the process doesn't exit before the timeout `Status` will be unified with `timeout`.
+%
+% `Options` is a a list of the following options
+%
+%  * timeout(Timeout) supported values for `Timeout` are 0 or `infinite`
+%
+% Each options may be specified at most once, when an option is not specified the following defaults apply:
+%
+% - timeout(infinite)
+%
+process_wait(Process, Status, Options) :- call_with_error_context(process_wait_(Process, Status, Options), predicate-process_wait/3).
+
+process_wait_(Process, Status, Options) :- 
+    valid_process(Process),
+    check_options(
+        [
+            option([timeout], valid_timeout, timeout(infinite), timeout(Timeout))
+        ],
+        Options,
+        process_wait_option
+    ),
+    '$process_wait'(Process, Exit, Timeout),
+    Exit = Status.
+
+valid_timeout(timeout(infinite)).
+valid_timeout(timeout(0)).
+
+
+%% process_kill(+Process).
+%
+% Kill the process using the process handle `Process`.
+% On Unix this sends SIGKILL.
+%
+% Only works for processes spawned with `process_create/3` that have not yet been release with `process_release/1`
+% 
+process_kill(Process) :- call_with_error_context(process_kill_(Process), predicate-process_kill/1).
+
+process_kill_(Process) :- 
+    valid_process(Process),
+    '$process_kill'(Process).
+
+%% process_release(+Process)
+%
+% wait for the process to exit (if not already) and release process handle `Process`
+%
+% It's an error if `Process` is not a valid process handle
+%
+process_release(Process) :- call_with_error_context(process_release_(Process), predicate-process_release/1).
+
+process_release_(Process) :- 
+    valid_process(Process),
+    process_wait(Process, _),
+    '$process_release'(Process).
+
+
+must_be_known_options(Valid, Options, Domain) :- call_with_error_context(must_be_known_options_(Valid, [], Options, Domain),predicate-must_be_known_options/3).
+
+must_be_known_options_(_, _,  [], _).
+must_be_known_options_(Valid, Found, [X|XS], Domain) :-
+    ( functor(X, Option, 1) -> true
+    ; domain_error(Domain, X, [])
+    ) ,
+    ( member(Option, Found) -> domain_error(non_duplicate_options, Option , [])
+    ; member(Option, Valid) -> true 
+    ; domain_error(Domain, Option, [])
+    ),
+    must_be_known_options_(Valid, [Option | Found], XS, Domain).
+
+check_options(KnownOptions, Options, Domain) :- call_with_error_context(check_options_(KnownOptions, Options, Domain), predicate-check_options/3).
+
+check_options_(KnownOptions, Options, Domain) :-
+    maplist(option_names, KnownOptions, Namess),
+    append(Namess, Names),
+    must_be_known_options(Names, Options, Domain),
+    extract_options(KnownOptions, Options).
+
+option_names(option(Names,_,_,_), Names).
+
+extract_options(KnownOptions, Options) :- call_with_error_context(extract_options_(KnownOptions, Options), predicate-extract_options/2).
+
+extract_options_([], _).
+extract_options_([X | XS], Options) :- 
+    option(Kinds, Pred, Default, Choice) = X,
+    tfilter(find_option(Kinds), Options, Solutions),
+    ( Solutions = [] -> Choice = Default
+    ; Solutions = [Provided] -> functor(Pred, Name, Arity), ArityP1 is Arity+1, call_with_error_context(call(Pred, Provided),predicate-Name/ArityP1), Choice = Provided 
+    ; domain_error(non_conflicting_options, Solutions, [])
+    ),
+    extract_options_(XS, Options).
+
+find_option(Names, Found, T) :- 
+    functor(Found, Name, 1), 
+    memberd_t(Name, Names, T).
+
+valid_stdio(IO) :- arg(1, IO, Arg), 
+    ( var(Arg) -> instantiation_error([]) 
+    ; valid_stdio_(Arg) -> true 
+    ; domain_error(stdio_spec, Arg, [])
+    ).
+
+valid_stdio_(std).
+valid_stdio_(null).
+valid_stdio_(pipe(Stream)) :- must_be(var, Stream).
+valid_stdio_(file(Path)) :- must_be(chars, Path).
+
+valid_env(env(E)) :- 
+    must_be(list, E),
+    ( valid_env_(E) -> true 
+    ; domain_error(process_create_option, env(E), [])
+    ).
+valid_env(environment(E)) :- 
+    must_be(list, E),
+    ( valid_env_(E) -> true 
+    ; domain_error(process_create_option, environment(E), [])
+    ).
+
+valid_env_([]).
+valid_env_([N=V|ES]) :- 
+    must_be(chars, N), 
+    must_be(chars, V),
+    valid_env_(ES).
+
+valid_uninit_process(process(Process)) :- must_be(var, Process).
+
+valid_process(Process) :- var(Process) -> instantiation_error([]) ; true.
+
+valid_cwd(cwd(Cwd)) :- must_be(chars, Cwd).
+
+simplify_env(E, [Kind, Envs1]) :- E =.. [Kind, Envs], simplify_env_(Envs, Envs1).
+
+simplify_env_([],[]).
+simplify_env_([N=V|E],[[N, V]|E1]) :- simplify_env_(E, E1).

src/lib/sgml.pl

@@ -96,14 +96,14 @@ is_sgml_source([]).
 is_sgml_source([C|Cs]) :- must_be(chars, [C|Cs]).
 
 load_structure_([], [], _, _).
-load_structure_([C|Cs], [E], Options, What) :-
+load_structure_([C|Cs], [E|Es], Options, What) :-
-        load_(What, [C|Cs], E, Options).
+        load_(What, [C|Cs], [E|Es], Options).
-load_structure_(file(Fs), [E], Options, What) :-
+load_structure_(file(Fs), [E|Es], Options, What) :-
         once(phrase_from_file(seq(Cs), Fs)),
-        load_(What, Cs, E, Options).
+        load_(What, Cs, [E|Es], Options).
-load_structure_(stream(Stream), [E], Options, What) :-
+load_structure_(stream(Stream), [E|Es], Options, What) :-
         get_n_chars(Stream, _, Cs),
-        load_(What, Cs, E, Options).
+        load_(What, Cs, [E|Es], Options).
 
 load_(html, Cs, E, Options) :- '$load_html'(Cs, E, Options).
 load_(xml, Cs, E, Options) :- '$load_xml'(Cs, E, Options).

src/loader.pl

@@ -299,7 +299,7 @@ expand_term_goals(Terms0, Terms) :-
           (  atom(Module) ->
              prolog_load_context(module, Target),
              module_expanded_head_variables(Head2, HeadVars),
-             catch(expand_goal(Body0, Target, Body1, HeadVars, []),
+             catch('$call'(loader:expand_goal(Body0, Target, Body1, HeadVars, [])),
                    error(type_error(callable, Pred), _),
                    (  loader:print_goal_expansion_warning(Pred),
                       builtins:(Body1 = Body0)
@@ -309,7 +309,7 @@ expand_term_goals(Terms0, Terms) :-
           )
        ;  module_expanded_head_variables(Head1, HeadVars),
           prolog_load_context(module, Target),
-          catch(expand_goal(Body0, Target, Body1, HeadVars, []),
+          catch('$call'(loader:expand_goal(Body0, Target, Body1, HeadVars, [])),
                 error(type_error(callable, Pred), _),
                 (  loader:print_goal_expansion_warning(Pred),
                    builtins:(Body1 = Body0)

src/machine/arithmetic_ops.rs

@@ -11,6 +11,7 @@ use crate::forms::*;
 use crate::heap_iter::*;
 use crate::machine::machine_errors::*;
 use crate::machine::machine_state::*;
+use crate::offset_table::*;
 use crate::parser::ast::*;
 use crate::parser::dashu::{Integer, Rational};
 use crate::types::*;
@@ -48,7 +49,7 @@ macro_rules! drop_iter_on_err {
     };
 }
 
-fn zero_divisor_eval_error(stub_gen: impl Fn() -> FunctorStub + 'static) -> MachineStubGen {
+fn zero_divisor_eval_error(stub_gen: impl Fn() -> MachineStub + 'static) -> MachineStubGen {
     Box::new(move |machine_st| {
         let eval_error = machine_st.evaluation_error(EvalError::ZeroDivisor);
         let stub = stub_gen();
@@ -57,7 +58,7 @@ fn zero_divisor_eval_error(stub_gen: impl Fn() -> FunctorStub + 'static) -> Mach
     })
 }
 
-fn undefined_eval_error(stub_gen: impl Fn() -> FunctorStub + 'static) -> MachineStubGen {
+fn undefined_eval_error(stub_gen: impl Fn() -> MachineStub + 'static) -> MachineStubGen {
     Box::new(move |machine_st| {
         let eval_error = machine_st.evaluation_error(EvalError::Undefined);
         let stub = stub_gen();
@@ -69,7 +70,7 @@ fn undefined_eval_error(stub_gen: impl Fn() -> FunctorStub + 'static) -> Machine
 fn numerical_type_error(
     valid_type: ValidType,
     n: Number,
-    stub_gen: impl Fn() -> FunctorStub + 'static,
+    stub_gen: impl Fn() -> MachineStub + 'static,
 ) -> MachineStubGen {
     Box::new(move |machine_st| {
         let type_error = machine_st.type_error(valid_type, n);
@@ -197,11 +198,10 @@ pub(crate) fn neg(n: Number, arena: &mut Arena) -> Number {
 pub(crate) fn abs(n: Number, arena: &mut Arena) -> Number {
     match n {
         Number::Fixnum(n) => {
-            if let Some(n) = n.get_num().checked_abs() {
+            if let Some(n) = n.checked_abs() {
-                fixnum!(Number, n, arena)
+                Number::Fixnum(n)
             } else {
-                let arena_int = Integer::from(n.get_num());
+                Number::arena_from(Integer::from(Fixnum::MAX + 1), arena)
-                Number::arena_from(arena_int.abs(), arena)
             }
         }
         Number::Integer(n) => {
@@ -528,7 +528,7 @@ pub(crate) fn min(n1: Number, n2: Number) -> Result<Number, MachineStubGen> {
 
 pub fn rational_from_number(
     n: Number,
-    stub_gen: impl Fn() -> FunctorStub + 'static,
+    stub_gen: impl Fn() -> MachineStub + 'static,
     arena: &mut Arena,
 ) -> Result<TypedArenaPtr<Rational>, MachineStubGen> {
     match n {
@@ -1104,7 +1104,7 @@ pub(crate) fn round(num: Number, arena: &mut Arena) -> Result<Number, MachineStu
 
 pub(crate) fn bitwise_complement(n1: Number, arena: &mut Arena) -> Result<Number, MachineStubGen> {
     match n1 {
-        Number::Fixnum(n) => Ok(Number::Fixnum(Fixnum::build_with(!n.get_num()))),
+        Number::Fixnum(n) => Ok(Number::Fixnum(!n)),
         Number::Integer(n1) => Ok(Number::arena_from(Integer::from(!&*n1), arena)),
         _ => {
             let stub_gen = || {
@@ -1124,9 +1124,12 @@ impl MachineState {
             &ArithmeticTerm::Reg(r) => {
                 let value = self.store(self.deref(self[r]));
 
-                match Number::try_from(value) {
+                match Number::try_from((value, &self.arena.f64_tbl)) {
                     Ok(n) => Ok(n),
-                    Err(_) => self.arith_eval_by_metacall(value),
+                    Err(_) => {
+                        self.heap[0] = value;
+                        self.arith_eval_by_metacall(0)
+                    }
                 }
             }
             &ArithmeticTerm::Interm(i) => Ok(mem::replace(
@@ -1140,7 +1143,7 @@ impl MachineState {
     pub fn get_rational(
         &mut self,
         at: &ArithmeticTerm,
-        caller: impl Fn() -> FunctorStub + 'static,
+        caller: impl Fn() -> MachineStub + 'static,
     ) -> Result<TypedArenaPtr<Rational>, MachineStub> {
         let n = self.get_number(at)?;
 
@@ -1152,11 +1155,11 @@ impl MachineState {
 
     pub(crate) fn arith_eval_by_metacall(
         &mut self,
-        value: HeapCellValue,
+        term_loc: usize,
     ) -> Result<Number, MachineStub> {
         let stub_gen = || functor_stub(atom!("is"), 2);
         let mut iter =
-            stackful_post_order_iter::<NonListElider>(&mut self.heap, &mut self.stack, value);
+            stackful_post_order_iter::<NonListElider>(&mut self.heap, &mut self.stack, term_loc);
 
         while let Some(value) = iter.next() {
             if value.get_forwarding_bit() {
@@ -1169,7 +1172,7 @@ impl MachineState {
                      (HeapCellValueTag::Str, s) => {
                          cell_as_atom_cell!(self.heap[s]).get_name_and_arity()
                      }
-                     (HeapCellValueTag::Lis | HeapCellValueTag::PStr | HeapCellValueTag::PStrOffset |
+                     (HeapCellValueTag::Lis | // HeapCellValueTag::PStr | HeapCellValueTag::PStrOffset |
                       HeapCellValueTag::PStrLoc) => {
                          (atom!("."), 2)
                      }
@@ -1385,8 +1388,9 @@ impl MachineState {
                 (HeapCellValueTag::Fixnum, n) => {
                     self.interms.push(Number::Fixnum(n));
                 }
-                (HeapCellValueTag::F64, fl) => {
+                (HeapCellValueTag::F64Offset, offset) => {
-                    self.interms.push(Number::Float(*fl));
+                    let fl = self.arena.f64_tbl.get_entry(offset);
+                    self.interms.push(Number::Float(fl));
                 }
                 (HeapCellValueTag::Cons, ptr) => {
                     match_untyped_arena_ptr!(ptr,
@@ -1449,7 +1453,7 @@ mod tests {
             parse_and_write_parsed_term_to_heap(&mut wam, "3 + 4 - 1 + 2.", &op_dir).unwrap();
 
         assert_eq!(
-            wam.arith_eval_by_metacall(heap_loc_as_cell!(term_write_result.heap_loc)),
+            wam.arith_eval_by_metacall(term_write_result.heap_loc),
             Ok(Number::Fixnum(Fixnum::build_with(8))),
         );
 
@@ -1459,7 +1463,7 @@ mod tests {
             parse_and_write_parsed_term_to_heap(&mut wam, "5 * 4 - 1.", &op_dir).unwrap();
 
         assert_eq!(
-            wam.arith_eval_by_metacall(heap_loc_as_cell!(term_write_result.heap_loc)),
+            wam.arith_eval_by_metacall(term_write_result.heap_loc),
             Ok(Number::Fixnum(Fixnum::build_with(19))),
         );
 
@@ -1469,7 +1473,7 @@ mod tests {
             parse_and_write_parsed_term_to_heap(&mut wam, "sign(-1).", &op_dir).unwrap();
 
         assert_eq!(
-            wam.arith_eval_by_metacall(heap_loc_as_cell!(term_write_result.heap_loc)),
+            wam.arith_eval_by_metacall(term_write_result.heap_loc),
             Ok(Number::Fixnum(Fixnum::build_with(-1)))
         );
     }

src/machine/attributed_variables.rs

@@ -6,7 +6,6 @@ use crate::types::*;
 use indexmap::IndexSet;
 
 use std::cmp::Ordering;
-use std::vec::IntoIter;
 
 pub(super) type Bindings = Vec<(usize, HeapCellValue)>;
 
@@ -55,32 +54,36 @@ impl MachineState {
         self.attr_var_init.bindings.push((h, addr));
     }
 
-    fn populate_var_and_value_lists(&mut self) -> (HeapCellValue, HeapCellValue) {
+    fn populate_var_and_value_lists(&mut self) -> Result<(HeapCellValue, HeapCellValue), usize> {
+        let size = self.attr_var_init.bindings.len();
+
         let iter = self
             .attr_var_init
             .bindings
             .iter()
             .map(|(ref h, _)| attr_var_as_cell!(*h));
 
-        let var_list_addr = heap_loc_as_cell!(iter_to_heap_list(&mut self.heap, iter));
+        let var_list_addr = sized_iter_to_heap_list(&mut self.heap, size, iter)?;
         let iter = self.attr_var_init.bindings.drain(0..).map(|(_, ref v)| *v);
-        let value_list_addr = heap_loc_as_cell!(iter_to_heap_list(&mut self.heap, iter));
+        let value_list_addr = sized_iter_to_heap_list(&mut self.heap, size, iter)?;
 
-        (var_list_addr, value_list_addr)
+        Ok((var_list_addr, value_list_addr))
     }
 
-    fn verify_attributes(&mut self) {
+    fn verify_attributes(&mut self) -> Result<(), usize> {
         for (h, _) in &self.attr_var_init.bindings {
             self.heap[*h] = attr_var_as_cell!(*h);
         }
 
-        let (var_list_addr, value_list_addr) = self.populate_var_and_value_lists();
+        let (var_list_addr, value_list_addr) = self.populate_var_and_value_lists()?;
 
         self[temp_v!(1)] = var_list_addr;
         self[temp_v!(2)] = value_list_addr;
+
+        Ok(())
     }
 
-    pub(super) fn gather_attr_vars_created_since(&mut self, b: usize) -> IntoIter<HeapCellValue> {
+    pub(super) fn gather_attr_vars_created_since(&mut self, b: usize) -> Vec<HeapCellValue> {
         let mut attr_vars: Vec<_> = if b >= self.attr_var_init.attr_var_queue.len() {
             vec![]
         } else {
@@ -104,10 +107,10 @@ impl MachineState {
         });
 
         attr_vars.dedup();
-        attr_vars.into_iter()
+        attr_vars
     }
 
-    pub(super) fn verify_attr_interrupt(&mut self, p: usize, arity: usize) {
+    pub(super) fn verify_attr_interrupt(&mut self, p: usize, arity: usize) -> Result<(), usize> {
         self.allocate(arity + 3);
 
         let e = self.e;
@@ -117,23 +120,40 @@ impl MachineState {
             and_frame[i] = self.registers[i];
         }
 
-        and_frame[arity + 1] = fixnum_as_cell!(Fixnum::build_with(self.b0 as i64));
+        and_frame[arity + 1] =
-        and_frame[arity + 2] = fixnum_as_cell!(Fixnum::build_with(self.num_of_args as i64));
+            fixnum_as_cell!(
-        and_frame[arity + 3] = fixnum_as_cell!(Fixnum::build_with(self.attr_var_init.cp as i64));
+                /* FIXME this is not safe */
+                unsafe { Fixnum::build_with_unchecked(self.b0 as i64) }
+            );
+        and_frame[arity + 2] =
+            fixnum_as_cell!(
+                /* FIXME this is not safe */
+                unsafe { Fixnum::build_with_unchecked(self.num_of_args as i64) }
+            );
+        and_frame[arity + 3] =
+            fixnum_as_cell!(
+                /* FIXME this is not safe */
+                unsafe { Fixnum::build_with_unchecked(self.attr_var_init.cp as i64) }
+            );
 
-        self.verify_attributes();
+        self.verify_attributes()?;
 
         self.num_of_args = 3;
         self.b0 = self.b;
         self.p = p;
+
+        Ok(())
     }
 
     pub(super) fn attr_vars_of_term(&mut self, cell: HeapCellValue) -> Vec<HeapCellValue> {
+        debug_assert!(cell.is_ref());
+
         let mut seen_set = IndexSet::new();
         let mut seen_vars = vec![];
 
-        let mut iter =
+        self.heap[0] = cell;
-            stackful_preorder_iter::<NonListElider>(&mut self.heap, &mut self.stack, cell);
+
+        let mut iter = stackful_preorder_iter::<NonListElider>(&mut self.heap, &mut self.stack, 0);
 
         while let Some(value) = iter.next() {
             read_heap_cell!(value,

src/machine/compile.rs

@@ -133,7 +133,7 @@ fn merge_indices(
             );
 
             retraction_info.push_record(RetractionRecord::AddedIndex(
-                skeleton[clause_index].opt_arg_index_key.clone(),
+                skeleton[clause_index].opt_arg_index_key,
                 clause_loc,
             ));
         } else {
@@ -246,7 +246,7 @@ fn remove_index_from_subsequence(
         // appear anywhere inside an Internal record.
         retraction_info.push_record(RetractionRecord::RemovedIndex(
             index_loc,
-            opt_arg_index_key.clone(),
+            *opt_arg_index_key,
             offset,
         ));
     }
@@ -700,31 +700,25 @@ fn remove_non_leading_clause(
     }
 }
 
-fn finalize_retract(
+fn finalize_retract<'a, LS: LoadState<'a>>(
+    payload: &mut <LS as LoadState<'a>>::LoaderFieldType,
     key: PredicateKey,
     compilation_target: CompilationTarget,
     skeleton: &mut PredicateSkeleton,
     code_index: CodeIndex,
     target_pos: usize,
     index_ptr_opt: Option<IndexPtr>,
-    retraction_info: &mut RetractionInfo,
 ) -> usize {
     let clause_clause_loc = delete_from_skeleton(
         compilation_target,
         key,
         skeleton,
         target_pos,
-        retraction_info,
+        &mut payload.retraction_info,
     );
 
     if let Some(index_ptr) = index_ptr_opt {
-        set_code_index(
+        set_code_index::<LS>(payload, &compilation_target, key, code_index, index_ptr);
-            retraction_info,
-            &compilation_target,
-            key,
-            code_index,
-            index_ptr,
-        );
     }
 
     clause_clause_loc
@@ -814,7 +808,7 @@ fn prepend_compiled_clause(
                 skeleton.clauses[0].clause_start = clause_loc + 2;
 
                 retraction_info.push_record(RetractionRecord::AddedIndex(
-                    skeleton.clauses[0].opt_arg_index_key.clone(),
+                    skeleton.clauses[0].opt_arg_index_key,
                     skeleton.clauses[0].clause_start,
                 ));
 
@@ -1076,7 +1070,7 @@ fn append_compiled_clause(
             skeleton.clauses[target_pos].opt_arg_index_key += index_loc - 1;
 
             retraction_info.push_record(RetractionRecord::AddedIndex(
-                skeleton.clauses[target_pos].opt_arg_index_key.clone(),
+                skeleton.clauses[target_pos].opt_arg_index_key,
                 skeleton.clauses[target_pos].clause_start,
             ));
 
@@ -1237,12 +1231,11 @@ impl<'a, LS: LoadState<'a>> Loader<'a, LS> {
         settings: CodeGenSettings,
     ) -> Result<StandaloneCompileResult, SessionError> {
         let mut preprocessor = Preprocessor::new(settings);
+        let clause = preprocessor.try_term_to_tl(self, term)?;
 
-        let clause = self.try_term_to_tl(term, &mut preprocessor)?;
+        let f64_tbl = &LS::machine_st(&mut self.payload).arena.f64_tbl;
-        // let queue = preprocessor.parse_queue(self)?;
-
-        let mut cg = CodeGenerator::new(&LS::machine_st(&mut self.payload).atom_tbl, settings);
 
+        let mut cg = CodeGenerator::new(f64_tbl, settings);
         let clause_code = cg.compile_predicate(vec![clause])?;
 
         Ok(StandaloneCompileResult {
@@ -1257,7 +1250,7 @@ impl<'a, LS: LoadState<'a>> Loader<'a, LS> {
         mut predicates: PredicateQueue,
         settings: CodeGenSettings,
     ) -> Result<CodeIndex, SessionError> {
-        let code_index = self.get_or_insert_code_index(key, predicates.compilation_target);
+        let code_idx = self.get_or_insert_code_index(key, predicates.compilation_target);
 
         LS::err_on_builtin_overwrite(self, key)?;
 
@@ -1268,11 +1261,12 @@ impl<'a, LS: LoadState<'a>> Loader<'a, LS> {
         let mut preprocessor = Preprocessor::new(settings);
 
         for term in predicates.predicates.drain(0..) {
-            clauses.push(self.try_term_to_tl(term, &mut preprocessor)?);
+            clauses.push(preprocessor.try_term_to_tl(self, term)?);
         }
 
-        let mut cg = CodeGenerator::new(&LS::machine_st(&mut self.payload).atom_tbl, settings);
+        let f64_tbl = &LS::machine_st(&mut self.payload).arena.f64_tbl;
 
+        let mut cg = CodeGenerator::new(f64_tbl, settings);
         let mut code = cg.compile_predicate(clauses)?;
 
         if settings.is_extensible {
@@ -1331,9 +1325,14 @@ impl<'a, LS: LoadState<'a>> Loader<'a, LS> {
             );
         }
 
+        let index_ptr = LS::machine_st(&mut self.payload)
+            .arena
+            .code_index_tbl
+            .get_entry(code_idx.into());
+
         print_overwrite_warning(
             &predicates.compilation_target,
-            code_index.get(),
+            index_ptr,
             key,
             settings.is_dynamic(),
         );
@@ -1344,16 +1343,16 @@ impl<'a, LS: LoadState<'a>> Loader<'a, LS> {
             IndexPtr::index(code_ptr)
         };
 
-        set_code_index(
+        set_code_index::<LS>(
-            &mut self.payload.retraction_info,
+            &mut self.payload,
             &predicates.compilation_target,
             key,
-            code_index,
+            code_idx,
             index_ptr,
         );
 
         self.wam_prelude.code.extend(code);
-        Ok(code_index)
+        Ok(code_idx)
     }
 
     fn extend_local_predicate_skeleton(
@@ -1555,19 +1554,19 @@ impl<'a, LS: LoadState<'a>> Loader<'a, LS> {
 
                 self.push_back_to_local_predicate_skeleton(&compilation_target, &key, code_len);
 
-                let code_index = self.get_or_insert_code_index(key, compilation_target);
+                let code_idx = self.get_or_insert_code_index(key, compilation_target);
 
                 if let Some(new_code_ptr) = result {
-                    set_code_index(
+                    set_code_index::<LS>(
-                        &mut self.payload.retraction_info,
+                        &mut self.payload,
                         &compilation_target,
                         key,
-                        code_index,
+                        code_idx,
                         new_code_ptr,
                     );
                 }
 
-                Ok(code_index)
+                Ok(code_idx)
             }
             AppendOrPrepend::Prepend => {
                 let clause_index_info = standalone_skeleton.clauses.pop_back().unwrap();
@@ -1597,17 +1596,17 @@ impl<'a, LS: LoadState<'a>> Loader<'a, LS> {
 
                 self.push_front_to_local_predicate_skeleton(&compilation_target, &key, code_len);
 
-                let code_index = self.get_or_insert_code_index(key, compilation_target);
+                let code_idx = self.get_or_insert_code_index(key, compilation_target);
 
-                set_code_index(
+                set_code_index::<LS>(
-                    &mut self.payload.retraction_info,
+                    &mut self.payload,
                     &compilation_target,
                     key,
-                    code_index,
+                    code_idx,
                     new_code_ptr,
                 );
 
-                Ok(code_index)
+                Ok(code_idx)
             }
         }
     }
@@ -1655,7 +1654,7 @@ impl<'a, LS: LoadState<'a>> Loader<'a, LS> {
 
     pub(super) fn retract_clause(&mut self, key: PredicateKey, target_pos: usize) -> usize {
         let payload_compilation_target = self.payload.compilation_target;
-        let code_index = self.get_or_insert_code_index(key, payload_compilation_target);
+        let code_idx_offset = self.get_or_insert_code_index(key, payload_compilation_target);
 
         let skeleton = self
             .wam_prelude
@@ -1733,14 +1732,14 @@ impl<'a, LS: LoadState<'a>> Loader<'a, LS> {
                             None
                         };
 
-                        return finalize_retract(
+                        return finalize_retract::<LS>(
+                            &mut self.payload,
                             key,
                             payload_compilation_target,
                             skeleton,
-                            code_index,
+                            code_idx_offset,
                             target_pos,
                             index_ptr_opt,
-                            &mut self.payload.retraction_info,
                         );
                     }
                     None => {
@@ -1762,14 +1761,14 @@ impl<'a, LS: LoadState<'a>> Loader<'a, LS> {
                             )
                         };
 
-                        return finalize_retract(
+                        return finalize_retract::<LS>(
+                            &mut self.payload,
                             key,
                             payload_compilation_target,
                             skeleton,
-                            code_index,
+                            code_idx_offset,
                             target_pos,
                             index_ptr_opt,
-                            &mut self.payload.retraction_info,
                         );
                     }
                 }
@@ -1992,14 +1991,14 @@ impl<'a, LS: LoadState<'a>> Loader<'a, LS> {
             }
         };
 
-        finalize_retract(
+        finalize_retract::<LS>(
+            &mut self.payload,
             key,
             payload_compilation_target,
             skeleton,
-            code_index,
+            code_idx_offset,
             target_pos,
             index_ptr_opt,
-            &mut self.payload.retraction_info,
         )
     }
 }
@@ -2226,18 +2225,22 @@ impl<'a, LS: LoadState<'a>> Loader<'a, LS> {
             };
 
             let predicates = self.payload.predicates.take();
-            let code_index = self.compile(key, predicates, settings)?;
+            let offset = self.compile(key, predicates, settings)?;
 
             if let Some(filename) = self.listing_src_file_name() {
                 if let Some(ref mut module) = self.wam_prelude.indices.modules.get_mut(&filename) {
-                    let index_ptr = code_index.get();
+                    let index_ptr = LS::machine_st(&mut self.payload)
-                    let code_index = *module.code_dir.entry(key).or_insert(code_index);
+                        .arena
+                        .code_index_tbl
+                        .get_entry(offset.into());
 
-                    set_code_index(
+                    let offset = *module.code_dir.entry(key).or_insert(offset);
-                        &mut self.payload.retraction_info,
+
+                    set_code_index::<LS>(
+                        &mut self.payload,
                         &CompilationTarget::Module(filename),
                         key,
-                        code_index,
+                        offset,
                         index_ptr,
                     );
                 }

src/machine/copier.rs

@@ -1,12 +1,71 @@
+use fxhash::FxBuildHasher;
+use indexmap::IndexSet;
+
 use crate::atom_table::*;
 use crate::machine::get_structure_index;
+use crate::machine::heap::*;
 use crate::machine::stack::*;
 use crate::types::*;
 
-use std::mem;
+use scryer_modular_bitfield::specifiers::*;
-use std::ops::IndexMut;
+use scryer_modular_bitfield::*;
 
-type Trail = Vec<(Ref, HeapCellValue)>;
+use std::collections::BTreeMap;
+use std::mem;
+use std::ops::{IndexMut, Range};
+
+#[derive(BitfieldSpecifier, Copy, Clone, Debug)]
+#[bits = 6]
+enum TrailRefTag {
+    HeapCell = 0b001011,
+    StackCell = 0b001101,
+    AttrVar = 0b010001,
+    PStrLoc = 0b001111,
+}
+
+#[bitfield]
+#[repr(u64)]
+#[derive(Copy, Clone, Debug, Hash, PartialEq, Eq)]
+struct TrailRef {
+    val: B56,
+    #[allow(unused)]
+    m: bool,
+    #[allow(unused)]
+    f: bool,
+    tag: TrailRefTag,
+}
+
+impl TrailRef {
+    #[inline(always)]
+    fn heap_cell(h: usize) -> Self {
+        TrailRef::new()
+            .with_tag(TrailRefTag::HeapCell)
+            .with_val(h as u64)
+    }
+
+    #[inline(always)]
+    fn stack_cell(h: usize) -> Self {
+        TrailRef::new()
+            .with_tag(TrailRefTag::StackCell)
+            .with_val(h as u64)
+    }
+
+    #[inline(always)]
+    fn attr_var(h: usize) -> Self {
+        TrailRef::new()
+            .with_tag(TrailRefTag::AttrVar)
+            .with_val(h as u64)
+    }
+
+    #[inline(always)]
+    fn pstr_loc(h: usize) -> Self {
+        TrailRef::new()
+            .with_tag(TrailRefTag::PStrLoc)
+            .with_val(h as u64)
+    }
+}
+
+type Trail = Vec<(TrailRef, HeapCellValue)>;
 
 #[derive(Debug, Clone, Copy)]
 pub enum AttrVarPolicy {
@@ -17,22 +76,39 @@ pub enum AttrVarPolicy {
 pub trait CopierTarget: IndexMut<usize, Output = HeapCellValue> {
     fn store(&self, value: HeapCellValue) -> HeapCellValue;
     fn deref(&self, value: HeapCellValue) -> HeapCellValue;
-    fn push(&mut self, value: HeapCellValue);
     fn push_attr_var_queue(&mut self, attr_var_loc: usize);
     fn stack(&mut self) -> &mut Stack;
     fn threshold(&self) -> usize;
+    // returns the tail location of the pstr on success
+    fn as_slice_from<'a>(&'a self, from: usize) -> Box<dyn Iterator<Item = u8> + 'a>;
+    fn copy_pstr_to_threshold(&mut self, pstr_loc: usize) -> Result<usize, usize>;
+    fn reserve(&mut self, num_cells: usize) -> Result<HeapWriter, usize>;
+    fn copy_slice_to_end(&mut self, bounds: Range<usize>) -> Result<(), usize>;
 }
 
 pub(crate) fn copy_term<T: CopierTarget>(
     target: T,
     addr: HeapCellValue,
     attr_var_policy: AttrVarPolicy,
-) {
+) -> Result<usize, usize> {
     let mut copy_term_state = CopyTermState::new(target, attr_var_policy);
+    let old_threshold = copy_term_state.target.threshold();
 
-    copy_term_state.copy_term_impl(addr);
+    copy_term_state.copy_term_impl(addr)?;
-    copy_term_state.copy_attr_var_lists();
+    copy_term_state.copy_attr_var_lists()?;
     copy_term_state.unwind_trail();
+
+    let new_threshold = copy_term_state.target.threshold();
+    copy_term_state.copy_pstrs()?;
+
+    Ok(new_threshold - old_threshold)
+}
+
+#[derive(Debug)]
+pub struct PStrData {
+    pre_old_h_tail_loc: usize,
+    post_old_h_tail_loc: usize,
+    post_old_h_pstr_loc_locs: IndexSet<usize, FxBuildHasher>,
 }
 
 #[derive(Debug)]
@@ -43,6 +119,9 @@ struct CopyTermState<T: CopierTarget> {
     target: T,
     attr_var_policy: AttrVarPolicy,
     attr_var_list_locs: Vec<(usize, HeapCellValue)>,
+    // keys of pstr_loc_locs are byte indices rounded down to the
+    // nearest cell boundary
+    pstr_loc_locs: BTreeMap<usize, PStrData>,
 }
 
 impl<T: CopierTarget> CopyTermState<T> {
@@ -54,6 +133,7 @@ impl<T: CopierTarget> CopyTermState<T> {
             target,
             attr_var_policy,
             attr_var_list_locs: vec![],
+            pstr_loc_locs: BTreeMap::new(),
         }
     }
 
@@ -64,17 +144,17 @@ impl<T: CopierTarget> CopyTermState<T> {
 
     fn trail_list_cell(&mut self, addr: usize, threshold: usize) {
         let trail_item = mem::replace(&mut self.target[addr], list_loc_as_cell!(threshold));
-        self.trail.push((Ref::heap_cell(addr), trail_item));
+        self.trail.push((TrailRef::heap_cell(addr), trail_item));
     }
 
-    fn copy_list(&mut self, addr: usize) {
+    fn copy_list(&mut self, addr: usize) -> Result<(), usize> {
         for offset in 0..2 {
             read_heap_cell!(self.target[addr + offset],
                 (HeapCellValueTag::Lis, h) => {
                     if h >= self.old_h {
                         *self.value_at_scan() = list_loc_as_cell!(h);
                         self.scan += 1;
-                        return;
+                        return Ok(());
                     }
                 }
                 _ => {
@@ -83,14 +163,10 @@ impl<T: CopierTarget> CopyTermState<T> {
         }
 
         let threshold = self.target.threshold();
+        self.target.copy_slice_to_end(addr..addr + 2)?;
 
         *self.value_at_scan() = list_loc_as_cell!(threshold);
 
-        for i in 0..2 {
-            let hcv = self.target[addr + i];
-            self.target.push(hcv);
-        }
-
         let cdr = self
             .target
             .store(self.target.deref(heap_loc_as_cell!(addr + 1)));
@@ -113,80 +189,108 @@ impl<T: CopierTarget> CopyTermState<T> {
         }
 
         self.scan += 1;
+        Ok(())
     }
 
-    fn copy_partial_string(&mut self, scan_tag: HeapCellValueTag, pstr_loc: usize) {
+    fn copy_partial_string(&mut self, pstr_loc: usize) -> Result<(), usize> {
-        read_heap_cell!(self.target[pstr_loc],
+        match self.pstr_loc_locs.range_mut(..=pstr_loc).next_back() {
-            (HeapCellValueTag::PStrLoc, h) => {
+            Some((
-                debug_assert!(h >= self.old_h);
+                _prev_pstr_loc,
-
+                &mut PStrData {
-                *self.value_at_scan() = match scan_tag {
+                    pre_old_h_tail_loc,
-                    HeapCellValueTag::PStrLoc => {
+                    ref mut post_old_h_pstr_loc_locs,
-                        pstr_loc_as_cell!(h)
+                    ..
-                    }
+                },
-                    tag => {
+            )) if pre_old_h_tail_loc >= cell_index!(pstr_loc) => {
-                        debug_assert_eq!(tag, HeapCellValueTag::PStrOffset);
+                post_old_h_pstr_loc_locs.insert(self.scan);
-                        pstr_offset_as_cell!(h)
-                    }
-                };
-
                 self.scan += 1;
-                return;
+                return Ok(());
-            }
-            (HeapCellValueTag::Var, h) => {
-                debug_assert!(h >= self.old_h);
-                debug_assert_eq!(scan_tag, HeapCellValueTag::PStrOffset);
-
-                *self.value_at_scan() = pstr_offset_as_cell!(h);
-                self.scan += 1;
-
-                return;
             }
             _ => {}
-        );
+        }
 
-        let threshold = self.target.threshold();
+        let offset = self
+            .target
+            .as_slice_from(pstr_loc)
+            .take_while(|b| *b != 0u8)
+            .count();
 
-        let replacement = read_heap_cell!(self.target[pstr_loc],
+        let left_pstr_boundary = cell_index!(pstr_loc + offset);
-            (HeapCellValueTag::CStr) => {
+        let flag = u64::from_be_bytes(self.target[left_pstr_boundary].into_bytes());
-                debug_assert_eq!(scan_tag, HeapCellValueTag::PStrOffset);
+        let pstr_loc_idx = cell_index!(pstr_loc);
 
-                *self.value_at_scan() = pstr_offset_as_cell!(threshold);
+        if flag == 1 {
-                self.target.push(self.target[pstr_loc]);
+            if left_pstr_boundary != pstr_loc_idx {
+                let mut pstr_data = self
+                    .pstr_loc_locs
+                    .remove(&heap_index!(left_pstr_boundary))
+                    .unwrap();
 
-                heap_loc_as_cell!(threshold)
+                pstr_data.post_old_h_pstr_loc_locs.insert(self.scan);
+                self.pstr_loc_locs
+                    .insert(heap_index!(cell_index!(pstr_loc)), pstr_data);
+
+                let old_cell = self.target[pstr_loc_idx];
+                self.target[pstr_loc_idx] = HeapCellValue::from_bytes(u64::to_be_bytes(1));
+                self.trail
+                    .push((TrailRef::pstr_loc(pstr_loc_idx), old_cell));
+            } else {
+                let pstr_data = self
+                    .pstr_loc_locs
+                    .get_mut(&heap_index!(left_pstr_boundary))
+                    .unwrap();
+                pstr_data.post_old_h_pstr_loc_locs.insert(self.scan);
             }
-            _ => {
+        } else {
-                *self.value_at_scan() = if scan_tag == HeapCellValueTag::PStrLoc {
+            let old_cell = self.target[pstr_loc_idx];
-                    pstr_loc_as_cell!(threshold)
+            self.target[pstr_loc_idx] = HeapCellValue::from_bytes(u64::to_be_bytes(1));
-                } else {
+            self.trail
-                    debug_assert_eq!(scan_tag, HeapCellValueTag::PStrOffset);
+                .push((TrailRef::pstr_loc(pstr_loc_idx), old_cell));
-                    pstr_offset_as_cell!(threshold)
-                };
 
-                self.target.push(self.target[pstr_loc]);
+            let old_tail_idx = if (pstr_loc + offset + 1) % Heap::heap_cell_alignment() == 0 {
-                self.target.push(self.target[pstr_loc + 1]);
+                cell_index!(pstr_loc + offset) + 2
+            } else {
+                cell_index!(pstr_loc + offset) + 1
+            };
 
-                pstr_loc_as_cell!(threshold)
+            let tail_cell = self.target[old_tail_idx];
-            }
+
-        );
+            let new_tail_idx = self.target.threshold();
+            let mut writer = self.target.reserve(1)?;
+
+            writer.write_with(|section| {
+                section.push_cell(tail_cell);
+            });
+
+            let mut post_old_h_pstr_loc_locs = IndexSet::with_hasher(FxBuildHasher::default());
+            post_old_h_pstr_loc_locs.insert(self.scan);
+
+            let pstr_data = PStrData {
+                pre_old_h_tail_loc: old_tail_idx,
+                post_old_h_tail_loc: new_tail_idx,
+                post_old_h_pstr_loc_locs,
+            };
+
+            self.pstr_loc_locs
+                .insert(heap_index!(pstr_loc_idx), pstr_data);
+        }
 
         self.scan += 1;
-
+        Ok(())
-        let trail_item = mem::replace(&mut self.target[pstr_loc], replacement);
-        self.trail.push((Ref::heap_cell(pstr_loc), trail_item));
     }
 
-    fn copy_attr_var_lists(&mut self) {
+    fn copy_attr_var_lists(&mut self) -> Result<(), usize> {
         while !self.attr_var_list_locs.is_empty() {
-            let iter = std::mem::take(&mut self.attr_var_list_locs);
+            let mut list_loc_vec = std::mem::take(&mut self.attr_var_list_locs);
 
-            for (threshold, list_loc) in iter {
+            while let Some((threshold, list_loc)) = list_loc_vec.pop() {
                 self.target[threshold] = list_loc_as_cell!(self.target.threshold());
                 self.target.push_attr_var_queue(threshold - 1);
-                self.copy_attr_var_list(list_loc);
+                self.copy_attr_var_list(list_loc)?;
             }
         }
+
+        Ok(())
     }
 
     /*
@@ -194,48 +298,49 @@ impl<T: CopierTarget> CopyTermState<T> {
      * structure which is ensured by this function and not at all by
      * the vanilla copier.
      */
-    fn copy_attr_var_list(&mut self, mut list_addr: HeapCellValue) {
+    fn copy_attr_var_list(&mut self, mut list_addr: HeapCellValue) -> Result<(), usize> {
         while let HeapCellValueTag::Lis = list_addr.get_tag() {
             let threshold = self.target.threshold();
             let heap_loc = list_addr.get_value() as usize;
             let str_loc = self.target[heap_loc].get_value() as usize;
+            let str_cell = self.target[str_loc];
+            let mut writer = self.target.reserve(3).unwrap();
 
-            self.target.push(heap_loc_as_cell!(threshold + 2));
+            writer.write_with(|section| {
-            self.target.push(heap_loc_as_cell!(threshold + 1));
+                section.push_cell(heap_loc_as_cell!(threshold + 2));
+                section.push_cell(heap_loc_as_cell!(threshold + 1));
 
-            read_heap_cell!(self.target[str_loc],
+                if str_cell.to_atom().is_some() {
-                (HeapCellValueTag::Atom) => {
+                    section.push_cell(str_cell);
-                    self.target.push(self.target[str_loc]);
                 }
-                (HeapCellValueTag::Str) => {
+            });
-                    self.copy_term_impl(self.target[str_loc]);
-                }
-                _ => {
-                    unreachable!();
-                }
-            );
 
+            debug_assert_eq!(str_cell.get_tag(), HeapCellValueTag::Str);
+
+            self.copy_term_impl(str_cell)?;
             list_addr = self.target[heap_loc + 1];
 
             if HeapCellValueTag::Lis == list_addr.get_tag() {
                 self.target[threshold + 1] = list_loc_as_cell!(self.target.threshold());
             }
         }
+
+        Ok(())
     }
 
-    fn reinstantiate_var(&mut self, addr: HeapCellValue, frontier: usize) {
+    fn reinstantiate_var(&mut self, addr: HeapCellValue, frontier: usize) -> Result<(), usize> {
         read_heap_cell!(addr,
             (HeapCellValueTag::Var, h) => {
                 self.target[frontier] = heap_loc_as_cell!(frontier);
                 self.target[h] = heap_loc_as_cell!(frontier);
 
-                self.trail.push((Ref::heap_cell(h), heap_loc_as_cell!(h)));
+                self.trail.push((TrailRef::heap_cell(h), heap_loc_as_cell!(h)));
             }
             (HeapCellValueTag::StackVar, s) => {
                 self.target[frontier] = heap_loc_as_cell!(frontier);
                 self.target.stack()[s] = heap_loc_as_cell!(frontier);
 
-                self.trail.push((Ref::stack_cell(s), stack_loc_as_cell!(s)));
+                self.trail.push((TrailRef::stack_cell(s), stack_loc_as_cell!(s)));
             }
             (HeapCellValueTag::AttrVar, h) => {
                 let threshold = if let AttrVarPolicy::DeepCopy = self.attr_var_policy {
@@ -247,14 +352,18 @@ impl<T: CopierTarget> CopyTermState<T> {
                 self.target[frontier] = heap_loc_as_cell!(threshold);
                 self.target[h] = heap_loc_as_cell!(threshold);
 
-                self.trail.push((Ref::attr_var(h), attr_var_as_cell!(h)));
+                self.trail.push((TrailRef::attr_var(h), attr_var_as_cell!(h)));
 
                 if let AttrVarPolicy::DeepCopy = self.attr_var_policy {
-                    self.target.push(attr_var_as_cell!(threshold));
+                    let mut writer = self.target.reserve(2)?;
-                    self.target.push(heap_loc_as_cell!(threshold + 1));
+
+                    writer.write_with(|section| {
+                        section.push_cell(attr_var_as_cell!(threshold));
+                        section.push_cell(heap_loc_as_cell!(threshold + 1));
+                    });
 
                     let old_list_link = self.target[h + 1];
-                    self.trail.push((Ref::heap_cell(h + 1), old_list_link));
+                    self.trail.push((TrailRef::heap_cell(h + 1), old_list_link));
                     self.target[h + 1] = heap_loc_as_cell!(threshold + 1);
 
                     if old_list_link.get_tag() == HeapCellValueTag::Lis {
@@ -266,9 +375,11 @@ impl<T: CopierTarget> CopyTermState<T> {
                 unreachable!()
             }
         );
+
+        Ok(())
     }
 
-    fn copy_var(&mut self, addr: HeapCellValue) {
+    fn copy_var(&mut self, addr: HeapCellValue) -> Result<(), usize> {
         let index = addr.get_value() as usize;
         let rd = self.target.deref(addr);
         let ra = self.target.store(rd);
@@ -278,7 +389,7 @@ impl<T: CopierTarget> CopyTermState<T> {
                 if h >= self.old_h {
                     *self.value_at_scan() = ra;
                     self.scan += 1;
-                    return;
+                    return Ok(());
                 }
             }
             (HeapCellValueTag::Lis, h) => {
@@ -292,47 +403,52 @@ impl<T: CopierTarget> CopyTermState<T> {
                     );
 
                     self.scan += 1;
-                    return;
+                    return Ok(());
                 }
             }
             _ => {}
         );
 
         if rd == ra {
-            self.reinstantiate_var(ra, self.scan);
+            self.reinstantiate_var(ra, self.scan)?;
             self.scan += 1;
         } else {
             *self.value_at_scan() = ra;
         }
+
+        Ok(())
     }
 
-    fn copy_structure(&mut self, addr: usize) {
+    fn copy_structure(&mut self, addr: usize) -> Result<(), usize> {
         read_heap_cell!(self.target[addr],
-            (HeapCellValueTag::Atom, (name, arity)) => {
+            (HeapCellValueTag::Atom, (_name, arity)) => {
                 let threshold = self.target.threshold();
 
-                *self.value_at_scan() = str_loc_as_cell!(threshold);
+                let index_cell = self.target[addr.saturating_sub(1)];
+
+                let str_cell = if get_structure_index(index_cell).is_some() {
+                    // copy the index pointer trailing this
+                    // inlined or expanded goal.
+                    let mut writer = self.target.reserve(1).unwrap();
+
+                    writer.write_with(|section| {
+                        section.push_cell(index_cell);
+                    });
+
+                    str_loc_as_cell!(threshold + 1)
+                } else {
+                    str_loc_as_cell!(threshold)
+                };
+
+                *self.value_at_scan() = str_cell;
+                self.target.copy_slice_to_end(addr .. addr + 1 + arity)?;
 
                 let trail_item = mem::replace(
                     &mut self.target[addr],
-                    str_loc_as_cell!(threshold),
+                    str_cell,
                 );
 
-                self.trail.push((Ref::heap_cell(addr), trail_item));
+                self.trail.push((TrailRef::heap_cell(addr), trail_item));
-                self.target.push(atom_as_cell!(name, arity));
-
-                for i in 0..arity {
-                    let hcv = self.target[addr + 1 + i];
-                    self.target.push(hcv);
-                }
-
-                let index_cell = self.target[addr + 1 + arity];
-
-                if get_structure_index(index_cell).is_some() {
-                    // copy the index pointer trailing this
-                    // inlined or expanded goal.
-                    self.target.push(index_cell);
-                }
             }
             (HeapCellValueTag::Str, h) => {
                 *self.value_at_scan() = str_loc_as_cell!(h);
@@ -343,11 +459,16 @@ impl<T: CopierTarget> CopyTermState<T> {
         );
 
         self.scan += 1;
+        Ok(())
     }
 
-    fn copy_term_impl(&mut self, addr: HeapCellValue) {
+    fn copy_term_impl(&mut self, addr: HeapCellValue) -> Result<(), usize> {
         self.scan = self.target.threshold();
-        self.target.push(addr);
+        let mut writer = self.target.reserve(1)?;
+
+        writer.write_with(|section| {
+            section.push_cell(addr);
+        });
 
         while self.scan < self.target.threshold() {
             let addr = *self.value_at_scan();
@@ -356,37 +477,64 @@ impl<T: CopierTarget> CopyTermState<T> {
                 (HeapCellValueTag::Lis, h) => {
                     if h >= self.old_h {
                         self.scan += 1;
+                        continue;
                     } else {
-                        self.copy_list(h);
+                        self.copy_list(h)
                     }
                 }
                 (HeapCellValueTag::AttrVar | HeapCellValueTag::Var) => {
-                    self.copy_var(addr);
+                    self.copy_var(addr)
                 }
                 (HeapCellValueTag::Str, h) => {
-                    self.copy_structure(h);
+                    self.copy_structure(h)
                 }
-                (HeapCellValueTag::PStrLoc | HeapCellValueTag::PStrOffset, pstr_loc) => {
+                (HeapCellValueTag::PStrLoc, pstr_loc) => {
-                    self.copy_partial_string(addr.get_tag(), pstr_loc);
+                    self.copy_partial_string(pstr_loc)
                 }
                 _ => {
                     self.scan += 1;
+                    continue;
                 }
-            );
+            )?;
         }
+
+        Ok(())
     }
 
-    fn unwind_trail(mut self) {
+    fn copy_pstrs(&mut self) -> Result<(), usize> {
-        for (r, value) in self.trail {
+        while let Some((least_pstr_loc, pstr_data)) = self.pstr_loc_locs.pop_first() {
-            let index = r.get_value() as usize;
+            let threshold = heap_index!(self.target.threshold());
 
-            match r.get_tag() {
+            for pstr_loc_loc in pstr_data.post_old_h_pstr_loc_locs {
-                RefTag::AttrVar | RefTag::HeapCell => {
+                let pstr_loc = self.target[pstr_loc_loc].get_value() as usize;
+                self.target[pstr_loc_loc] =
+                    pstr_loc_as_cell!(threshold + pstr_loc - least_pstr_loc);
+            }
+
+            self.target.copy_pstr_to_threshold(least_pstr_loc)?;
+
+            let mut writer = self.target.reserve(1)?;
+
+            writer.write_with(|section| {
+                section.push_cell(heap_loc_as_cell!(pstr_data.post_old_h_tail_loc));
+            });
+        }
+
+        Ok(())
+    }
+
+    fn unwind_trail(&mut self) {
+        for (r, value) in self.trail.drain(..) {
+            let index = r.val() as usize;
+
+            match r.tag() {
+                TrailRefTag::AttrVar | TrailRefTag::HeapCell => {
                     self.target[index] = value;
                     self.target[index].set_mark_bit(false);
                     self.target[index].set_forwarding_bit(false);
                 }
-                RefTag::StackCell => self.target.stack()[index] = value,
+                TrailRefTag::StackCell => self.target.stack()[index] = value,
+                TrailRefTag::PStrLoc => self.target[index] = value,
             }
         }
     }
@@ -395,19 +543,26 @@ impl<T: CopierTarget> CopyTermState<T> {
 #[cfg(test)]
 mod tests {
     use super::*;
+    use crate::functor_macro::*;
     use crate::machine::mock_wam::*;
 
     #[test]
     fn copier_tests() {
         let mut wam = MockWAM::new();
 
+        // clear the heap of resource error data etc
+        wam.machine_st.heap.clear();
+
         let f_atom = atom!("f");
         let a_atom = atom!("a");
         let b_atom = atom!("b");
 
-        wam.machine_st
+        let mut functor_writer = Heap::functor_writer(functor!(
-            .heap
+            f_atom,
-            .extend(functor!(f_atom, [atom(a_atom), atom(b_atom)]));
+            [atom_as_cell(a_atom), atom_as_cell(b_atom)]
+        ));
+
+        functor_writer(&mut wam.machine_st.heap).unwrap();
 
         assert_eq!(wam.machine_st.heap[0], atom_as_cell!(f_atom, 2));
         assert_eq!(wam.machine_st.heap[1], atom_as_cell!(a_atom));
@@ -415,7 +570,7 @@ mod tests {
 
         {
             let wam = TermCopyingMockWAM { wam: &mut wam };
-            copy_term(wam, str_loc_as_cell!(0), AttrVarPolicy::DeepCopy);
+            copy_term(wam, str_loc_as_cell!(0), AttrVarPolicy::DeepCopy).unwrap();
         }
 
         // check that the original heap state is still intact.
@@ -430,69 +585,266 @@ mod tests {
 
         wam.machine_st.heap.clear();
 
-        let pstr_var_cell =
+        let mut writer = wam.machine_st.heap.reserve(4).unwrap();
-            put_partial_string(&mut wam.machine_st.heap, "abc ", &wam.machine_st.atom_tbl);
-        let pstr_cell = wam.machine_st.heap[pstr_var_cell.get_value() as usize];
 
-        wam.machine_st.heap.pop();
+        writer.write_with(|section| {
-        wam.machine_st.heap.push(pstr_loc_as_cell!(2));
+            section.push_pstr("abc ");
+            section.push_cell(pstr_loc_as_cell!(heap_index!(2)));
 
-        let pstr_second_var_cell =
+            section.push_pstr("def");
-            put_partial_string(&mut wam.machine_st.heap, "def", &wam.machine_st.atom_tbl);
+            section.push_cell(pstr_loc_as_cell!(0));
-        let pstr_second_cell = wam.machine_st.heap[pstr_second_var_cell.get_value() as usize];
+        });
-
-        wam.machine_st.heap.pop();
-        wam.machine_st
-            .heap
-            .push(pstr_loc_as_cell!(wam.machine_st.heap.len() + 1));
-
-        wam.machine_st.heap.push(pstr_offset_as_cell!(0));
-        wam.machine_st
-            .heap
-            .push(fixnum_as_cell!(Fixnum::build_with(0i64)));
 
         {
             let wam = TermCopyingMockWAM { wam: &mut wam };
-            copy_term(wam, pstr_loc_as_cell!(0), AttrVarPolicy::DeepCopy);
+            copy_term(wam, pstr_loc_as_cell!(0), AttrVarPolicy::DeepCopy).unwrap();
         }
 
-        print_heap_terms(wam.machine_st.heap[6..].iter(), 6);
+        assert_eq!(wam.machine_st.heap.slice_to_str(0, "abc ".len()), "abc ");
-
+        assert_eq!(wam.machine_st.heap[1], pstr_loc_as_cell!(heap_index!(2)));
-        assert_eq!(wam.machine_st.heap[0], pstr_cell);
-        assert_eq!(wam.machine_st.heap[1], pstr_loc_as_cell!(2));
-        assert_eq!(wam.machine_st.heap[2], pstr_second_cell);
-        assert_eq!(wam.machine_st.heap[3], pstr_loc_as_cell!(4));
-        assert_eq!(wam.machine_st.heap[4], pstr_offset_as_cell!(0));
         assert_eq!(
-            wam.machine_st.heap[5],
+            wam.machine_st
-            fixnum_as_cell!(Fixnum::build_with(0i64))
+                .heap
+                .slice_to_str(heap_index!(2), "def".len()),
+            "def"
         );
+        assert_eq!(wam.machine_st.heap[3], pstr_loc_as_cell!(0));
+
+        assert_eq!(wam.machine_st.heap[4], pstr_loc_as_cell!(heap_index!(7)));
+        assert_eq!(wam.machine_st.heap[5], pstr_loc_as_cell!(heap_index!(9)));
+        assert_eq!(wam.machine_st.heap[6], pstr_loc_as_cell!(heap_index!(7)));
 
-        assert_eq!(wam.machine_st.heap[7], pstr_cell);
-        assert_eq!(wam.machine_st.heap[8], pstr_loc_as_cell!(9));
-        assert_eq!(wam.machine_st.heap[9], pstr_second_cell);
-        assert_eq!(wam.machine_st.heap[10], pstr_loc_as_cell!(11));
-        assert_eq!(wam.machine_st.heap[11], pstr_offset_as_cell!(7));
         assert_eq!(
-            wam.machine_st.heap[12],
+            wam.machine_st
-            fixnum_as_cell!(Fixnum::build_with(0i64))
+                .heap
+                .slice_to_str(heap_index!(7), "abc ".len()),
+            "abc "
         );
+        assert_eq!(wam.machine_st.heap[8], heap_loc_as_cell!(5));
+        assert_eq!(
+            wam.machine_st
+                .heap
+                .slice_to_str(heap_index!(9), "def".len()),
+            "def"
+        );
+        assert_eq!(wam.machine_st.heap[10], heap_loc_as_cell!(6));
 
         wam.machine_st.heap.clear();
 
-        wam.machine_st.heap.extend(functor!(
+        let mut writer = wam.machine_st.heap.reserve(4).unwrap();
-            f_atom,
+
-            [
+        writer.write_with(|section| {
-                atom(a_atom),
+            section.push_pstr("abc ");
-                atom(b_atom),
+            section.push_cell(pstr_loc_as_cell!(heap_index!(2) + 9));
-                atom(a_atom),
+
-                cell(str_loc_as_cell!(0))
+            section.push_pstr("defdefdefdef");
-            ]
+            section.push_cell(pstr_loc_as_cell!(0));
-        ));
+        });
 
         {
             let wam = TermCopyingMockWAM { wam: &mut wam };
-            copy_term(wam, str_loc_as_cell!(0), AttrVarPolicy::DeepCopy);
+            copy_term(wam, pstr_loc_as_cell!(0), AttrVarPolicy::DeepCopy).unwrap();
+        }
+
+        assert_eq!(wam.machine_st.heap.slice_to_str(0, "abc ".len()), "abc ");
+        assert_eq!(
+            wam.machine_st.heap[1],
+            pstr_loc_as_cell!(heap_index!(2) + 9)
+        );
+        assert_eq!(
+            wam.machine_st
+                .heap
+                .slice_to_str(heap_index!(2), "defdefdefdef".len()),
+            "defdefdefdef"
+        );
+        assert_eq!(wam.machine_st.heap[4], pstr_loc_as_cell!(0));
+
+        assert_eq!(wam.machine_st.heap[5], pstr_loc_as_cell!(heap_index!(8)));
+        assert_eq!(
+            wam.machine_st.heap[6],
+            pstr_loc_as_cell!(heap_index!(10) + 1)
+        );
+        assert_eq!(wam.machine_st.heap[7], pstr_loc_as_cell!(heap_index!(8)));
+
+        assert_eq!(
+            wam.machine_st
+                .heap
+                .slice_to_str(heap_index!(8), "abc ".len()),
+            "abc "
+        );
+        assert_eq!(wam.machine_st.heap[9], heap_loc_as_cell!(6));
+        assert_eq!(
+            wam.machine_st
+                .heap
+                .slice_to_str(heap_index!(10), "fdef".len()),
+            "fdef"
+        );
+        assert_eq!(wam.machine_st.heap[11], heap_loc_as_cell!(7));
+
+        wam.machine_st.heap.clear();
+
+        let mut writer = wam.machine_st.heap.reserve(4).unwrap();
+
+        writer.write_with(|section| {
+            section.push_pstr("012345678912345");
+            section.push_cell(pstr_loc_as_cell!(heap_index!(0)));
+        });
+
+        {
+            let wam = TermCopyingMockWAM { wam: &mut wam };
+            copy_term(wam, pstr_loc_as_cell!(0), AttrVarPolicy::DeepCopy).unwrap();
+        }
+
+        assert_eq!(
+            wam.machine_st.heap.slice_to_str(0, "012345678912345".len()),
+            "012345678912345"
+        );
+        assert_eq!(wam.machine_st.heap[3], pstr_loc_as_cell!(heap_index!(0)));
+
+        assert_eq!(wam.machine_st.heap[4], pstr_loc_as_cell!(heap_index!(6)));
+
+        assert_eq!(
+            wam.machine_st
+                .heap
+                .slice_to_str(heap_index!(6), "012345678912345".len()),
+            "012345678912345"
+        );
+        assert_eq!(wam.machine_st.heap[5], pstr_loc_as_cell!(heap_index!(6)));
+
+        wam.machine_st.heap.clear();
+
+        let mut writer = wam.machine_st.heap.reserve(4).unwrap();
+
+        writer.write_with(|section| {
+            section.push_pstr("012345678912345");
+            section.push_cell(pstr_loc_as_cell!(heap_index!(0) + 9));
+        });
+
+        {
+            let wam = TermCopyingMockWAM { wam: &mut wam };
+            copy_term(wam, pstr_loc_as_cell!(0), AttrVarPolicy::DeepCopy).unwrap();
+        }
+
+        assert_eq!(
+            wam.machine_st.heap.slice_to_str(0, "012345678912345".len()),
+            "012345678912345"
+        );
+        assert_eq!(
+            wam.machine_st.heap[3],
+            pstr_loc_as_cell!(heap_index!(0) + 9)
+        );
+
+        assert_eq!(wam.machine_st.heap[4], pstr_loc_as_cell!(heap_index!(6)));
+        assert_eq!(
+            wam.machine_st.heap[5],
+            pstr_loc_as_cell!(heap_index!(6) + 9)
+        );
+
+        assert_eq!(
+            wam.machine_st
+                .heap
+                .slice_to_str(heap_index!(6), "012345678912345".len()),
+            "012345678912345"
+        );
+        assert_eq!(wam.machine_st.heap[9], heap_loc_as_cell!(5));
+
+        wam.machine_st.heap.clear();
+
+        let mut writer = wam.machine_st.heap.reserve(4).unwrap();
+
+        writer.write_with(|section| {
+            section.push_pstr("012345678912345");
+            section.push_cell(pstr_loc_as_cell!(heap_index!(0) + 7));
+        });
+
+        {
+            let wam = TermCopyingMockWAM { wam: &mut wam };
+            copy_term(wam, pstr_loc_as_cell!(11), AttrVarPolicy::DeepCopy).unwrap();
+        }
+
+        assert_eq!(
+            wam.machine_st.heap.slice_to_str(0, "012345678912345".len()),
+            "012345678912345"
+        );
+        assert_eq!(
+            wam.machine_st.heap[3],
+            pstr_loc_as_cell!(heap_index!(0) + 7)
+        );
+
+        assert_eq!(
+            wam.machine_st.heap[4],
+            pstr_loc_as_cell!(heap_index!(6) + 11)
+        );
+        assert_eq!(
+            wam.machine_st.heap[5],
+            pstr_loc_as_cell!(heap_index!(6) + 7)
+        );
+
+        assert_eq!(
+            wam.machine_st
+                .heap
+                .slice_to_str(heap_index!(6), "012345678912345".len()),
+            "012345678912345"
+        );
+        assert_eq!(wam.machine_st.heap[9], heap_loc_as_cell!(5));
+
+        wam.machine_st.heap.clear();
+
+        let mut writer = wam.machine_st.heap.reserve(4).unwrap();
+
+        writer.write_with(|section| {
+            section.push_pstr("012345678912345");
+            section.push_cell(pstr_loc_as_cell!(heap_index!(0) + 12));
+        });
+
+        {
+            let wam = TermCopyingMockWAM { wam: &mut wam };
+            copy_term(wam, pstr_loc_as_cell!(11), AttrVarPolicy::DeepCopy).unwrap();
+        }
+
+        assert_eq!(
+            wam.machine_st.heap.slice_to_str(0, "012345678912345".len()),
+            "012345678912345"
+        );
+        assert_eq!(
+            wam.machine_st.heap[3],
+            pstr_loc_as_cell!(heap_index!(0) + 12)
+        );
+
+        assert_eq!(
+            wam.machine_st.heap[4],
+            pstr_loc_as_cell!(heap_index!(6) + 3)
+        );
+        assert_eq!(
+            wam.machine_st.heap[5],
+            pstr_loc_as_cell!(heap_index!(6) + 4)
+        );
+
+        assert_eq!(
+            wam.machine_st
+                .heap
+                .slice_to_str(heap_index!(6), "8912345".len()),
+            "8912345"
+        );
+        assert_eq!(wam.machine_st.heap[8], heap_loc_as_cell!(5));
+
+        wam.machine_st.heap.clear();
+
+        let mut functor_writer = Heap::functor_writer(functor!(
+            f_atom,
+            [
+                atom_as_cell(a_atom),
+                atom_as_cell(b_atom),
+                atom_as_cell(a_atom),
+                str_loc_as_cell(0)
+            ]
+        ));
+
+        functor_writer(&mut wam.machine_st.heap).unwrap();
+
+        {
+            let wam = TermCopyingMockWAM { wam: &mut wam };
+            copy_term(wam, str_loc_as_cell!(0), AttrVarPolicy::DeepCopy).unwrap();
         }
 
         assert_eq!(wam.machine_st.heap[0], atom_as_cell!(f_atom, 4));
@@ -500,7 +852,6 @@ mod tests {
         assert_eq!(wam.machine_st.heap[2], atom_as_cell!(b_atom));
         assert_eq!(wam.machine_st.heap[3], atom_as_cell!(a_atom));
         assert_eq!(wam.machine_st.heap[4], str_loc_as_cell!(0));
-
         assert_eq!(wam.machine_st.heap[5], str_loc_as_cell!(6));
         assert_eq!(wam.machine_st.heap[6], atom_as_cell!(f_atom, 4));
         assert_eq!(wam.machine_st.heap[7], atom_as_cell!(a_atom));

src/machine/cycle_detection.rs

@@ -1,4 +1,5 @@
 use crate::atom_table::*;
+use crate::machine::heap::*;
 use crate::types::*;
 
 /* Use the pointer reversal technique of the Deutsch-Schorr-Waite
@@ -11,7 +12,7 @@ use crate::types::*;
  * - Cells are only marked during the backward phase
  * - Visiting subterms of a visited compound does not immediately shift to the backward phase
  * - The heads of LIS structures are both marked and forwarded rather
- *   than just forwarded to distinguish them from tails;
+ *   than just forwarded to distinguish them from tails
  *   continue_forwarding() checks for this before entering the forward
  *   phase
  *
@@ -22,7 +23,7 @@ use crate::types::*;
 
 #[derive(Debug)]
 pub(crate) struct CycleDetectingIter<'a, const STOP_AT_CYCLES: bool> {
-    pub(crate) heap: &'a mut [HeapCellValue],
+    pub(crate) heap: &'a mut Heap,
     start: usize,
     current: usize,
     next: u64,
@@ -31,7 +32,7 @@ pub(crate) struct CycleDetectingIter<'a, const STOP_AT_CYCLES: bool> {
 }
 
 impl<'a, const STOP_AT_CYCLES: bool> CycleDetectingIter<'a, STOP_AT_CYCLES> {
-    pub(crate) fn new(heap: &'a mut [HeapCellValue], start: usize) -> Self {
+    pub(crate) fn new(heap: &'a mut Heap, start: usize) -> Self {
         heap[start].set_forwarding_bit(true);
         let next = heap[start].get_value();
 
@@ -127,7 +128,7 @@ impl<'a, const STOP_AT_CYCLES: bool> CycleDetectingIter<'a, STOP_AT_CYCLES> {
                         self.current = next;
                         self.next = temp;
 
-                        if self.next < self.heap.len() as u64 {
+                        if self.next < self.heap.cell_len() as u64 {
                             return Some(HeapCellValue::build_with(tag, next as u64));
                         }
                     }
@@ -136,10 +137,7 @@ impl<'a, const STOP_AT_CYCLES: bool> CycleDetectingIter<'a, STOP_AT_CYCLES> {
                         let cell = self.heap[h];
                         let arity = cell_as_atom_cell!(self.heap[h]).get_arity();
 
-                        let last_cell_loc = match self.traverse_subterm(h + 1, arity) {
+                        let last_cell_loc = self.traverse_subterm(h + 1, arity)?;
-                            Some(last_cell_loc) => last_cell_loc,
-                            None => return None,
-                        };
 
                         if last_cell_loc == h {
                             if self.backward() {
@@ -170,10 +168,7 @@ impl<'a, const STOP_AT_CYCLES: bool> CycleDetectingIter<'a, STOP_AT_CYCLES> {
                         let mut cell = self.heap[self.current];
                         cell.set_value(self.next);
 
-                        let last_cell_loc = match self.traverse_subterm(self.next as usize, 2) {
+                        let last_cell_loc = self.traverse_subterm(self.next as usize, 2)?;
-                            Some(last_cell_loc) => last_cell_loc,
-                            None => return None,
-                        };
 
                         if self.cycle_detection_active() {
                             for idx in (self.next as usize..last_cell_loc).rev() {
@@ -205,10 +200,9 @@ impl<'a, const STOP_AT_CYCLES: bool> CycleDetectingIter<'a, STOP_AT_CYCLES> {
                     }
                     HeapCellValueTag::PStrLoc => {
                         let h = self.next as usize;
-                        let cell = self.heap[h];
+                        let tail_idx = self.heap.scan_slice_to_str(h).tail_idx;
-                        let last_cell_loc = h + 1;
 
-                        if self.heap[last_cell_loc].get_forwarding_bit() {
+                        if self.heap[tail_idx].get_forwarding_bit() {
                             if self.cycle_detection_active() {
                                 self.cycle_found = true;
                                 return None;
@@ -219,45 +213,13 @@ impl<'a, const STOP_AT_CYCLES: bool> CycleDetectingIter<'a, STOP_AT_CYCLES> {
                             continue;
                         }
 
-                        self.heap[last_cell_loc].set_forwarding_bit(true);
+                        self.heap[tail_idx].set_forwarding_bit(true);
 
-                        self.next = self.heap[last_cell_loc].get_value();
+                        self.next = self.heap[tail_idx].get_value();
-                        self.heap[last_cell_loc].set_value(self.current as u64);
+                        self.heap[tail_idx].set_value(self.current as u64);
-                        self.current = last_cell_loc;
+                        self.current = tail_idx;
 
-                        return Some(cell);
+                        return Some(pstr_loc_as_cell!(h));
-                    }
-                    HeapCellValueTag::PStrOffset => {
-                        let h = self.next as usize;
-                        let cell = self.heap[h];
-                        let last_cell_loc = h + 1;
-
-                        if self.heap[h].get_tag() == HeapCellValueTag::PStr {
-                            if self.heap[last_cell_loc].get_forwarding_bit() {
-                                if self.cycle_detection_active() {
-                                    self.cycle_found = true;
-                                    return None;
-                                } else if self.backward() {
-                                    return None;
-                                }
-
-                                continue;
-                            }
-
-                            self.heap[last_cell_loc].set_forwarding_bit(true);
-
-                            self.next = self.heap[last_cell_loc].get_value();
-                            self.heap[last_cell_loc].set_value(self.current as u64);
-                            self.current = last_cell_loc;
-                        } else {
-                            debug_assert!(self.heap[h].get_tag() == HeapCellValueTag::CStr);
-
-                            self.next = self.heap[h].get_value();
-                            self.heap[h].set_value(self.current as u64);
-                            self.current = h;
-                        }
-
-                        return Some(cell);
                     }
                     tag @ HeapCellValueTag::Atom => {
                         let cell = HeapCellValue::build_with(tag, self.next);
@@ -269,11 +231,6 @@ impl<'a, const STOP_AT_CYCLES: bool> CycleDetectingIter<'a, STOP_AT_CYCLES> {
                             return None;
                         }
                     }
-                    HeapCellValueTag::PStr => {
-                        if self.backward() {
-                            return None;
-                        }
-                    }
                     _ => {
                         return Some(self.backward_and_return());
                     }

src/machine/disjuncts.rs

@@ -200,10 +200,12 @@ impl VarData {
 
             match build_stack.front_mut() {
                 Some(ChunkedTerms::Branch(_)) => {
-                    build_stack.push_front(ChunkedTerms::Chunk(VecDeque::from(vec![term])));
+                    build_stack.push_front(ChunkedTerms::Chunk {
+                        terms: VecDeque::from(vec![term]),
+                    });
                 }
-                Some(ChunkedTerms::Chunk(chunk)) => {
+                Some(ChunkedTerms::Chunk { terms, .. }) => {
-                    chunk.push_front(term);
+                    terms.push_front(term);
                 }
                 None => {
                     unreachable!()
@@ -423,7 +425,6 @@ impl VariableClassifier {
                         // "probe_head_var". note the difference between it
                         // and "probe_body_var".
                         let branch_info_v = self.branch_map.entry(var_ptr.clone()).or_default();
-
                         let needs_new_branch = branch_info_v.is_empty();
 
                         if needs_new_branch {
@@ -578,7 +579,7 @@ impl VariableClassifier {
                             mut terms,
                         ) if terms.len() == 3 => {
                             if let Some(last_arg) = terms.last() {
-                                if let Term::Literal(_, Literal::CodeIndex(_)) = last_arg {
+                                if let Term::Literal(_, Literal::CodeIndexOffset(_)) = last_arg {
                                     terms.pop();
                                     state_stack.push(TraversalState::Term(Term::Clause(
                                         Cell::default(),
@@ -801,7 +802,7 @@ impl VariableClassifier {
                                 self.call_policy,
                             ));
                         }
-                        Term::Literal(_, Literal::Atom(atom!("!")) | Literal::Char('!')) => {
+                        Term::Literal(_, Literal::Atom(atom!("!"))) => {
                             let (var_num, is_global) =
                                 if let Some(var_num) = self.global_cut_var_num_override {
                                     (var_num, false)
@@ -879,10 +880,10 @@ impl BranchMap {
 
                     for var_info in chunk.vars.iter_mut() {
                         if var_info.lvl == Level::Shallow {
-                            let term_loc = var_info.chunk_type.to_gen_context(chunk.chunk_num);
+                            let context = var_info.chunk_type.to_gen_context(chunk.chunk_num);
                             temp_var_data
                                 .use_set
-                                .insert((term_loc, var_info.classify_info.arg_c));
+                                .insert((context, var_info.classify_info.arg_c));
                         }
                     }
 

src/machine/lib_machine/mod.rs

@@ -1,14 +1,15 @@
 use std::cmp::Ordering;
 use std::collections::BTreeMap;
+use std::rc::Rc;
 
 use crate::atom_table;
 use crate::heap_iter::{stackful_post_order_iter, NonListElider};
 use crate::machine::machine_indices::VarKey;
 use crate::machine::mock_wam::CompositeOpDir;
 use crate::machine::{
-    ArenaHeaderTag, F64Offset, F64Ptr, Fixnum, Number, BREAK_FROM_DISPATCH_LOOP_LOC,
+    ArenaHeaderTag, Fixnum, Number, BREAK_FROM_DISPATCH_LOOP_LOC, LIB_QUERY_SUCCESS,
-    LIB_QUERY_SUCCESS,
 };
+use crate::offset_table::*;
 use crate::parser::ast::{Var, VarPtr};
 use crate::parser::parser::{Parser, Tokens};
 use crate::read::{write_term_to_heap, TermWriteResult};
@@ -175,10 +176,13 @@ impl Term {
     ) -> Self {
         // Adapted from MachineState::read_term_from_heap
         let mut term_stack = vec![];
-        let iter = stackful_post_order_iter::<NonListElider>(
+
+        machine.machine_st.heap[0] = heap_cell;
+
+        let mut iter = stackful_post_order_iter::<NonListElider>(
             &mut machine.machine_st.heap,
             &mut machine.machine_st.stack,
-            heap_cell,
+            0,
         );
 
         let mut anon_count: usize = 0;
@@ -193,7 +197,7 @@ impl Term {
             },
         };
 
-        for addr in iter {
+        while let Some(addr) = iter.next() {
             let addr = unmark_cell_bits!(addr);
 
             read_heap_cell!(addr,
@@ -244,11 +248,11 @@ impl Term {
                 (HeapCellValueTag::Var | HeapCellValueTag::AttrVar | HeapCellValueTag::StackVar) => {
                     let var = var_names.get(&addr).map(|x| x.borrow().clone());
                     match var {
-                        Some(Var::Named(name)) => term_stack.push(Term::Var(name)),
+                        Some(Var::Named(name)) => term_stack.push(Term::Var(name.as_ref().to_owned())),
                         _ => {
                             let anon_name = loop {
                                 // Generate a name for the anonymous variable
-                                let anon_name = count_to_letter_code(anon_count);
+                                let anon_name = Rc::new(count_to_letter_code(anon_count));
 
                                 // Find if this name is already being used
                                 var_names.sort_by(|_, a, _, b| {
@@ -269,21 +273,19 @@ impl Term {
                                     },
                                 }
                             };
-                            term_stack.push(Term::Var(anon_name));
+                            term_stack.push(Term::Var(anon_name.as_ref().to_owned()));
                         },
                     }
                 }
-                (HeapCellValueTag::F64, f) => {
+                (HeapCellValueTag::F64Offset, offset) => {
-                    term_stack.push(Term::Float((*f).into()));
+                    let f = machine.machine_st.arena.f64_tbl.get_entry(offset);
-                }
+                    term_stack.push(Term::Float(f.into()));
-                (HeapCellValueTag::Char, c) => {
-                    term_stack.push(Term::Atom(c.into()));
                 }
                 (HeapCellValueTag::Fixnum, n) => {
                     term_stack.push(Term::Integer(n.into()));
                 }
                 (HeapCellValueTag::Cons, ptr) => {
-                    if let Ok(n) = Number::try_from(addr) {
+                    if let Ok(n) = Number::try_from((addr, &machine.machine_st.arena.f64_tbl)) {
                         match n {
                             Number::Integer(i) => term_stack.push(Term::Integer((*i).clone())),
                             Number::Rational(r) => term_stack.push(Term::Rational((*r).clone())),
@@ -296,7 +298,7 @@ impl Term {
                                     Term::atom(alias.as_str().to_string())
                                 } else {
                                     Term::compound("$stream", [
-                                        Term::integer(stream.as_ptr() as usize)
+                                        Term::integer(stream.as_ptr().addr())
                                     ])
                                 };
                                 term_stack.push(stream_term);
@@ -310,35 +312,7 @@ impl Term {
                         );
                     }
                 }
-                (HeapCellValueTag::CStr, s) => {
-                    term_stack.push(Term::String(s.as_str().to_string()));
-                }
                 (HeapCellValueTag::Atom, (name, arity)) => {
-                    //let h = iter.focus().value() as usize;
-                    //let mut arity = arity;
-
-                    // Not sure why/if this is needed.
-                    // Might find out with better testing later.
-                    /*
-                    if iter.heap.len() > h + arity + 1 {
-                        let value = iter.heap[h + arity + 1];
-
-                        if let Some(idx) = get_structure_index(value) {
-                            // in the second condition, arity == 0,
-                            // meaning idx cannot pertain to this atom
-                            // if it is the direct subterm of a larger
-                            // structure.
-                            if arity > 0 || !iter.direct_subterm_of_str(h) {
-                                term_stack.push(
-                                    Term::Literal(Cell::default(), Literal::CodeIndex(idx))
-                                );
-
-                                arity += 1;
-                            }
-                        }
-                    }
-                    */
-
                     if arity == 0 {
                         let atom_name = name.as_str().to_string();
                         if atom_name == "[]" {
@@ -354,8 +328,9 @@ impl Term {
                         term_stack.push(Term::Compound(name.as_str().to_string(), subterms));
                     }
                 }
-                (HeapCellValueTag::PStr, atom) => {
+                (HeapCellValueTag::PStrLoc, pstr_loc) => {
                     let tail = term_stack.pop().unwrap();
+                    let char_iter = iter.base_iter.heap.char_iter(pstr_loc);
 
                     match tail {
                         Term::Atom(atom) => {
@@ -363,21 +338,18 @@ impl Term {
                                 term_stack.push(Term::String(atom.as_str().to_string()));
                             }
                         },
+                        Term::List(l) if l.is_empty() => {
+                            term_stack.push(Term::String(char_iter.collect()));
+                        }
                         Term::List(l) => {
-                            let mut list: Vec<Term> = atom
+                            let mut list: Vec<Term> = char_iter
-                                .as_str()
-                                .to_string()
-                                .chars()
                                 .map(|x| Term::Atom(x.to_string()))
                                 .collect();
                             list.extend(l.into_iter());
                             term_stack.push(Term::List(list));
                         },
                         _ => {
-                            let mut list: Vec<Term> = atom
+                            let mut list: Vec<Term> = char_iter
-                                .as_str()
-                                .to_string()
-                                .chars()
                                 .map(|x| Term::Atom(x.to_string()))
                                 .collect();
 
@@ -403,19 +375,6 @@ impl Term {
                         }
                     }
                 }
-                // I dont know if this is needed here.
-                /*
-                (HeapCellValueTag::PStrLoc, h) => {
-                    let atom = cell_as_atom_cell!(iter.heap[h]).get_name();
-                    let tail = term_stack.pop().unwrap();
-
-                    term_stack.push(Term::PartialString(
-                        Cell::default(),
-                        atom.as_str().to_owned(),
-                        Box::new(tail),
-                    ));
-                }
-                */
                 _ => {
                     unreachable!();
                 }
@@ -467,11 +426,20 @@ impl Iterator for QueryState<'_> {
             // this should halt the search for solutions as it
             // does in the Scryer top-level. the exception term is
             // contained in self.machine_st.ball.
-            let h = machine.machine_st.heap.len();
+            let h = machine.machine_st.heap.cell_len();
-            machine
+
+            if let Err(resource_err_loc) = machine
                 .machine_st
                 .heap
-                .extend(machine.machine_st.ball.stub.clone());
+                .append(&machine.machine_st.ball.stub)
+            {
+                return Some(Err(Term::from_heapcell(
+                    machine,
+                    machine.machine_st.heap[resource_err_loc],
+                    &mut IndexMap::new(),
+                )));
+            }
+
             let exception_term =
                 Term::from_heapcell(machine, machine.machine_st.heap[h], &mut var_names.clone());
 
@@ -503,7 +471,7 @@ impl Iterator for QueryState<'_> {
             let mut var_name = var_key.to_string();
             if var_name.starts_with('_') {
                 let should_print = var_names.values().any(|x| match x.borrow().clone() {
-                    Var::Named(v) => v == var_name,
+                    Var::Named(v) => *v == *var_name,
                     _ => false,
                 });
                 if !should_print {
@@ -522,10 +490,10 @@ impl Iterator for QueryState<'_> {
                 // Var dict is in the order things appear in the query. If var_name appears
                 // after term in the query, switch their places.
                 let var_name_idx = var_dict
-                    .get_index_of(&VarKey::VarPtr(Var::Named(var_name.clone()).into()))
+                    .get_index_of(&VarKey::VarPtr(Var::from(var_name.clone()).into()))
                     .unwrap();
                 let term_idx =
-                    var_dict.get_index_of(&VarKey::VarPtr(Var::Named(term_str.clone()).into()));
+                    var_dict.get_index_of(&VarKey::VarPtr(Var::from(term_str.clone()).into()));
                 if let Some(idx) = term_idx {
                     if idx < var_name_idx {
                         let new_term = Term::Var(var_name);
@@ -559,7 +527,7 @@ impl Machine {
     /// Consults a module into the [`Machine`] from a string.
     pub fn consult_module_string(&mut self, module_name: &str, program: impl Into<String>) {
         let stream = Stream::from_owned_string(program.into(), &mut self.machine_st.arena);
-        self.machine_st.registers[1] = stream.into();
+        self.machine_st.registers[1] = stream_as_cell!(stream);
         self.machine_st.registers[2] = atom_as_cell!(&atom_table::AtomTable::build_with(
             &self.machine_st.atom_tbl,
             module_name
@@ -588,7 +556,7 @@ impl Machine {
         or_frame.prelude.attr_var_queue_len = 0;
 
         self.machine_st.b = stub_b;
-        self.machine_st.hb = self.machine_st.heap.len();
+        self.machine_st.hb = self.machine_st.heap.cell_len();
         self.machine_st.block = stub_b;
     }
 
@@ -606,9 +574,8 @@ impl Machine {
         self.allocate_stub_choice_point();
 
         // Write parsed term to heap
-        let term_write_result =
+        let term_write_result = write_term_to_heap(&term, &mut self.machine_st.heap)
-            write_term_to_heap(&term, &mut self.machine_st.heap, &self.machine_st.atom_tbl)
+            .expect("couldn't write term to heap");
-                .expect("couldn't write term to heap");
 
         let var_names: IndexMap<_, _> = term_write_result
             .var_dict
@@ -630,9 +597,15 @@ impl Machine {
             .indices
             .code_dir
             .get(&(atom!("call"), 1))
-            .expect("couldn't get code index")
+            .cloned()
-            .local()
+            .map(|offset| {
-            .unwrap();
+                self.machine_st
+                    .arena
+                    .code_index_tbl
+                    .get_entry(offset.into())
+                    .p() as usize
+            })
+            .expect("couldn't get code index");
 
         self.machine_st.execute_at_index(1, call_index_p);
 

src/machine/load_state.rs

@@ -2,7 +2,6 @@ use crate::forms::*;
 use crate::machine::loader::*;
 use crate::machine::machine_errors::*;
 use crate::machine::machine_indices::*;
-use crate::machine::preprocessor::*;
 use crate::machine::term_stream::*;
 use crate::machine::*;
 use crate::parser::ast::*;
@@ -16,35 +15,38 @@ use std::mem;
 
 pub(super) type ModuleOpExports = Vec<(OpDecl, Option<OpDesc>)>;
 
-pub(super) fn set_code_index(
+pub(super) fn set_code_index<'a, LS: LoadState<'a>>(
-    retraction_info: &mut RetractionInfo,
+    payload: &mut <LS as LoadState<'a>>::LoaderFieldType,
     compilation_target: &CompilationTarget,
     key: PredicateKey,
-    mut code_index: CodeIndex,
+    code_idx: CodeIndex,
     code_ptr: IndexPtr,
 ) {
-    let record = match compilation_target {
+    let record = LS::machine_st(payload).arena.code_index_tbl.with_entry_mut(
-        CompilationTarget::User => {
+        code_idx.into(),
-            if IndexPtrTag::Undefined == code_index.get().tag() {
+        |code_idx_ptr| match compilation_target {
-                code_index.set(code_ptr);
+            CompilationTarget::User => {
-                RetractionRecord::AddedUserPredicate(key)
+                if IndexPtrTag::Undefined == code_idx_ptr.tag() {
-            } else {
+                    *code_idx_ptr = code_ptr;
-                let replaced = code_index.replace(code_ptr);
+                    RetractionRecord::AddedUserPredicate(key)
-                RetractionRecord::ReplacedUserPredicate(key, replaced)
+                } else {
+                    let replaced = mem::replace(code_idx_ptr, code_ptr);
+                    RetractionRecord::ReplacedUserPredicate(key, replaced)
+                }
             }
-        }
+            CompilationTarget::Module(ref module_name) => {
-        CompilationTarget::Module(ref module_name) => {
+                if IndexPtrTag::Undefined == code_idx_ptr.tag() {
-            if IndexPtrTag::Undefined == code_index.get().tag() {
+                    *code_idx_ptr = code_ptr;
-                code_index.set(code_ptr);
+                    RetractionRecord::AddedModulePredicate(*module_name, key)
-                RetractionRecord::AddedModulePredicate(*module_name, key)
+                } else {
-            } else {
+                    let replaced = mem::replace(code_idx_ptr, code_ptr);
-                let replaced = code_index.replace(code_ptr);
+                    RetractionRecord::ReplacedModulePredicate(*module_name, key, replaced)
-                RetractionRecord::ReplacedModulePredicate(*module_name, key, replaced)
+                }
             }
-        }
+        },
-    };
+    );
 
-    retraction_info.push_record(record);
+    payload.retraction_info.push_record(record);
 }
 
 fn add_op_decl_as_module_export<'a, LS: LoadState<'a>>(
@@ -134,21 +136,28 @@ pub(super) fn import_module_exports<'a, LS: LoadState<'a>>(
                 }
 
                 if let Some(src_code_index) = imported_module.code_dir.get(&key).cloned() {
-                    let arena = &mut LS::machine_st(payload).arena;
+                    let code_idx_tbl = &mut LS::machine_st(payload).arena.code_index_tbl;
 
                     let target_code_index = *code_dir
                         .entry(key)
-                        .or_insert_with(|| CodeIndex::default(arena));
+                        .or_insert_with(|| CodeIndex::default(code_idx_tbl));
 
-                    set_code_index(
+                    let src_code_index_ptr = code_idx_tbl.get_entry(src_code_index.into());
-                        &mut payload.retraction_info,
+
+                    set_code_index::<LS>(
+                        payload,
                         compilation_target,
                         key,
                         target_code_index,
-                        src_code_index.get(),
+                        src_code_index_ptr,
                     );
 
-                    if src_code_index.is_dynamic_undefined() {
+                    if LS::machine_st(payload)
+                        .arena
+                        .code_index_tbl
+                        .get_entry(src_code_index.into())
+                        .is_dynamic_undefined()
+                    {
                         code_dir.insert(key, src_code_index);
                     }
                 } else {
@@ -190,19 +199,20 @@ fn import_module_exports_into_module<'a, LS: LoadState<'a>>(
                     meta_predicates.insert(key, meta_specs.clone());
                 }
 
-                if let Some(src_code_index) = imported_module.code_dir.get(&key) {
+                if let Some(src_code_index) = imported_module.code_dir.get(&key).cloned() {
-                    let arena = &mut LS::machine_st(payload).arena;
+                    let code_index_tbl = &mut LS::machine_st(payload).arena.code_index_tbl;
 
+                    let src_code_ptr = code_index_tbl.get_entry(src_code_index.into());
                     let target_code_index = *code_dir
                         .entry(key)
-                        .or_insert_with(|| CodeIndex::default(arena));
+                        .or_insert_with(|| CodeIndex::default(code_index_tbl));
 
-                    set_code_index(
+                    set_code_index::<LS>(
-                        &mut payload.retraction_info,
+                        payload,
                         compilation_target,
                         key,
                         target_code_index,
-                        src_code_index.get(),
+                        src_code_ptr,
                     );
                 } else {
                     return Err(SessionError::ModuleDoesNotContainExport(
@@ -243,21 +253,21 @@ fn import_qualified_module_exports<'a, LS: LoadState<'a>>(
                         .insert(key, meta_specs.clone());
                 }
 
-                if let Some(src_code_index) = imported_module.code_dir.get(&key) {
+                if let Some(src_code_index) = imported_module.code_dir.get(&key).cloned() {
-                    let arena = &mut LS::machine_st(payload).arena;
+                    let code_index_tbl = &mut LS::machine_st(payload).arena.code_index_tbl;
 
-                    let target_code_index = *wam_prelude
+                    let src_code_ptr = code_index_tbl.get_entry(src_code_index.into());
-                        .indices
+                    let target_code_index =
-                        .code_dir
+                        *wam_prelude.indices.code_dir.entry(key).or_insert_with(|| {
-                        .entry(key)
+                            CodeIndex::new(IndexPtr::undefined(), code_index_tbl)
-                        .or_insert_with(|| CodeIndex::new(IndexPtr::undefined(), arena));
+                        });
 
-                    set_code_index(
+                    set_code_index::<LS>(
-                        &mut payload.retraction_info,
+                        payload,
                         compilation_target,
                         key,
                         target_code_index,
-                        src_code_index.get(),
+                        src_code_ptr,
                     );
                 } else {
                     return Err(SessionError::ModuleDoesNotContainExport(
@@ -304,19 +314,20 @@ fn import_qualified_module_exports_into_module<'a, LS: LoadState<'a>>(
                     meta_predicates.insert(key, meta_specs.clone());
                 }
 
-                if let Some(src_code_index) = imported_module.code_dir.get(&key) {
+                if let Some(src_code_index) = imported_module.code_dir.get(&key).cloned() {
-                    let arena = &mut LS::machine_st(payload).arena;
+                    let code_index_tbl = &mut LS::machine_st(payload).arena.code_index_tbl;
 
+                    let src_code_ptr = code_index_tbl.get_entry(src_code_index.into());
                     let target_code_index = *code_dir
                         .entry(key)
-                        .or_insert_with(|| CodeIndex::new(IndexPtr::undefined(), arena));
+                        .or_insert_with(|| CodeIndex::new(IndexPtr::undefined(), code_index_tbl));
 
-                    set_code_index(
+                    set_code_index::<LS>(
-                        &mut payload.retraction_info,
+                        payload,
                         &payload_compilation_target,
                         key,
                         target_code_index,
-                        src_code_index.get(),
+                        src_code_ptr,
                     );
                 } else {
                     return Err(SessionError::ModuleDoesNotContainExport(
@@ -434,19 +445,6 @@ impl<'a, LS: LoadState<'a>> Loader<'a, LS> {
         self.retract_local_clauses_impl(clause_clause_compilation_target, key, clause_locs);
     }
 
-    pub(super) fn try_term_to_tl(
-        &mut self,
-        term: Term,
-        preprocessor: &mut Preprocessor,
-    ) -> Result<PredicateClause, SessionError> {
-        let tl = preprocessor.try_term_to_tl(self, term)?;
-
-        Ok(match tl {
-            TopLevel::Fact(fact, var_data) => PredicateClause::Fact(fact, var_data),
-            TopLevel::Rule(rule, var_data) => PredicateClause::Rule(rule, var_data),
-        })
-    }
-
     #[inline]
     pub(super) fn remove_module_op_exports(&mut self) {
         for (mut op_decl, record) in self.payload.module_op_exports.drain(0..) {
@@ -482,11 +480,14 @@ impl<'a, LS: LoadState<'a>> Loader<'a, LS> {
                     .indices
                     .get_predicate_skeleton(local_compilation_target, key)
                 {
-                    let old_index_ptr = code_index.replace(if global_skeleton.core.is_dynamic {
+                    let old_index_ptr = code_index.replace(
-                        IndexPtr::dynamic_undefined()
+                        &mut LS::machine_st(&mut self.payload).arena.code_index_tbl,
-                    } else {
+                        if global_skeleton.core.is_dynamic {
-                        IndexPtr::undefined()
+                            IndexPtr::dynamic_undefined()
-                    });
+                        } else {
+                            IndexPtr::undefined()
+                        },
+                    );
 
                     self.payload.retraction_info.push_record(
                         RetractionRecord::ReplacedModulePredicate(module_name, *key, old_index_ptr),
@@ -500,8 +501,11 @@ impl<'a, LS: LoadState<'a>> Loader<'a, LS> {
                 continue;
             }
 
-            if !code_index.is_undefined() && !code_index.is_dynamic_undefined() {
+            let code_index_tbl = &mut LS::machine_st(&mut self.payload).arena.code_index_tbl;
-                let old_index_ptr = code_index.replace(IndexPtr::undefined());
+            let code_ptr = code_index_tbl.get_entry((*code_index).into());
+
+            if !code_ptr.is_undefined() && !code_ptr.is_dynamic_undefined() {
+                let old_index_ptr = code_index.replace(code_index_tbl, IndexPtr::undefined());
 
                 self.payload.retraction_info.push_record(
                     RetractionRecord::ReplacedModulePredicate(module_name, *key, old_index_ptr),
@@ -531,27 +535,32 @@ impl<'a, LS: LoadState<'a>> Loader<'a, LS> {
             None => return,
         };
 
-        fn remove_module_exports(
+        fn remove_module_exports<'b, LS: LoadState<'b>>(
+            payload: &mut <LS as LoadState<'b>>::LoaderFieldType,
             removed_module: &Module,
             code_dir: &mut CodeDir,
             op_dir: &mut OpDir,
-            retraction_info: &mut RetractionInfo,
             predicate_retractor: impl Fn(PredicateKey, IndexPtr) -> RetractionRecord,
             op_retractor: impl Fn(OpDecl, OpDesc) -> RetractionRecord,
         ) {
             for export in removed_module.module_decl.exports.iter() {
                 match export {
                     ModuleExport::PredicateKey(ref key) => {
-                        match (removed_module.code_dir.get(key), code_dir.get_mut(key)) {
+                        if let (Some(module_code_idx), Some(target_code_idx)) = (
-                            (Some(module_code_index), Some(target_code_index))
+                            removed_module.code_dir.get(key).cloned(),
-                                if module_code_index.get() == target_code_index.get() =>
+                            code_dir.get_mut(key).cloned(),
-                            {
+                        ) {
+                            let code_index_tbl = &mut LS::machine_st(payload).arena.code_index_tbl;
+                            let module_code_ptr = code_index_tbl.get_entry(module_code_idx.into());
+                            let target_code_ptr = code_index_tbl.get_entry(target_code_idx.into());
+
+                            if module_code_ptr == target_code_ptr {
                                 let old_index_ptr =
-                                    target_code_index.replace(IndexPtr::undefined());
+                                    target_code_idx.replace(code_index_tbl, IndexPtr::undefined());
-                                retraction_info
+                                payload
+                                    .retraction_info
                                     .push_record(predicate_retractor(*key, old_index_ptr));
                             }
-                            _ => {}
                         }
                     }
                     ModuleExport::OpDecl(op_decl) => {
@@ -559,7 +568,9 @@ impl<'a, LS: LoadState<'a>> Loader<'a, LS> {
                             .swap_remove(&(op_decl.name, op_decl.op_desc.get_spec().fixity()));
 
                         if let Some(op_desc) = op_dir_value_opt {
-                            retraction_info.push_record(op_retractor(*op_decl, op_desc));
+                            payload
+                                .retraction_info
+                                .push_record(op_retractor(*op_decl, op_desc));
                         }
                     }
                 }
@@ -568,11 +579,11 @@ impl<'a, LS: LoadState<'a>> Loader<'a, LS> {
 
         match self.payload.compilation_target {
             CompilationTarget::User => {
-                remove_module_exports(
+                remove_module_exports::<LS>(
+                    &mut self.payload,
                     &removed_module,
                     &mut self.wam_prelude.indices.code_dir,
                     &mut self.wam_prelude.indices.op_dir,
-                    &mut self.payload.retraction_info,
                     RetractionRecord::ReplacedUserPredicate,
                     RetractionRecord::ReplacedUserOp,
                 );
@@ -592,11 +603,11 @@ impl<'a, LS: LoadState<'a>> Loader<'a, LS> {
                     .modules
                     .get_mut(&target_module_name)
                 {
-                    remove_module_exports(
+                    remove_module_exports::<LS>(
+                        &mut self.payload,
                         &removed_module,
                         &mut module.code_dir,
                         &mut module.op_dir,
-                        &mut self.payload.retraction_info,
                         predicate_retractor,
                         op_retractor,
                     );
@@ -622,7 +633,7 @@ impl<'a, LS: LoadState<'a>> Loader<'a, LS> {
             Some(ref mut module) => *module.code_dir.entry(key).or_insert_with(|| {
                 CodeIndex::new(
                     IndexPtr::undefined(),
-                    &mut LS::machine_st(&mut self.payload).arena,
+                    &mut LS::machine_st(&mut self.payload).arena.code_index_tbl,
                 )
             }),
             None => {
@@ -632,7 +643,7 @@ impl<'a, LS: LoadState<'a>> Loader<'a, LS> {
                     Some(ref mut module) => *module.code_dir.entry(key).or_insert_with(|| {
                         CodeIndex::new(
                             IndexPtr::undefined(),
-                            &mut LS::machine_st(&mut self.payload).arena,
+                            &mut LS::machine_st(&mut self.payload).arena.code_index_tbl,
                         )
                     }),
                     None => {
@@ -648,7 +659,7 @@ impl<'a, LS: LoadState<'a>> Loader<'a, LS> {
         key: PredicateKey,
         compilation_target: CompilationTarget,
     ) -> CodeIndex {
-        let arena = &mut LS::machine_st(&mut self.payload).arena;
+        let code_index_tbl = &mut LS::machine_st(&mut self.payload).arena.code_index_tbl;
 
         match compilation_target {
             CompilationTarget::User => *self
@@ -656,7 +667,7 @@ impl<'a, LS: LoadState<'a>> Loader<'a, LS> {
                 .indices
                 .code_dir
                 .entry(key)
-                .or_insert_with(|| CodeIndex::new(IndexPtr::undefined(), arena)),
+                .or_insert_with(|| CodeIndex::new(IndexPtr::undefined(), code_index_tbl)),
             CompilationTarget::Module(module_name) => {
                 self.get_or_insert_local_code_index(module_name, key)
             }
@@ -668,15 +679,15 @@ impl<'a, LS: LoadState<'a>> Loader<'a, LS> {
         module_name: Atom,
         key: PredicateKey,
     ) -> CodeIndex {
-        let arena = &mut LS::machine_st(&mut self.payload).arena;
+        let code_index_tbl = &mut LS::machine_st(&mut self.payload).arena.code_index_tbl;
 
         if module_name == atom!("user") {
-            return *self
+            *self
                 .wam_prelude
                 .indices
                 .code_dir
                 .entry(key)
-                .or_insert_with(|| CodeIndex::new(IndexPtr::undefined(), arena));
+                .or_insert_with(|| CodeIndex::new(IndexPtr::undefined(), code_index_tbl))
         } else {
             self.get_or_insert_local_code_index(module_name, key)
         }

src/machine/loader.rs

@@ -20,6 +20,7 @@ use std::collections::VecDeque;
 use std::convert::TryFrom;
 use std::fmt;
 use std::ops::{Deref, DerefMut};
+use std::rc::Rc;
 
 /*
  * The loader compiles Prolog terms read from a TermStream instance,
@@ -382,7 +383,6 @@ impl<'a> LoadState<'a> for BootstrappingLoadState<'a> {
         let repo_len = loader.wam_prelude.code.len();
 
         loader.payload.retraction_info.reset(repo_len);
-
         loader.remove_module_op_exports();
 
         Ok(loader.payload.compilation_target)
@@ -720,7 +720,9 @@ impl<'a, LS: LoadState<'a>> Loader<'a, LS> {
                         self.wam_prelude.indices.modules.get_mut(&module_name)
                     {
                         if let Some(code_idx) = module.code_dir.get_mut(&key) {
-                            code_idx.set(old_code_idx)
+                            let code_index_tbl =
+                                &mut LS::machine_st(&mut self.payload).arena.code_index_tbl;
+                            code_idx.set(code_index_tbl, old_code_idx);
                         }
                     }
                 }
@@ -741,7 +743,9 @@ impl<'a, LS: LoadState<'a>> Loader<'a, LS> {
                 }
                 RetractionRecord::ReplacedUserPredicate(key, old_code_idx) => {
                     if let Some(code_idx) = self.wam_prelude.indices.code_dir.get_mut(&key) {
-                        code_idx.set(old_code_idx)
+                        let code_index_tbl =
+                            &mut LS::machine_st(&mut self.payload).arena.code_index_tbl;
+                        code_idx.set(code_index_tbl, old_code_idx)
                     }
                 }
                 RetractionRecord::AddedIndex(index_key, clause_loc) => {
@@ -762,7 +766,7 @@ impl<'a, LS: LoadState<'a>> Loader<'a, LS> {
                             ) => {
                                 remove_constant_indices(
                                     constant,
-                                    &overlapping_constants,
+                                    overlapping_constants,
                                     indexing_code,
                                     clause_loc - index_loc, // WAS: &inner_index_locs,
                                 );
@@ -1046,8 +1050,7 @@ impl<'a, LS: LoadState<'a>> Loader<'a, LS> {
         let cell = machine_st[r];
 
         let export_list = machine_st.read_term_from_heap(cell);
-        let atom_tbl = &mut LS::machine_st(&mut self.payload).atom_tbl;
+        let export_list = setup_module_export_list(export_list)?;
-        let export_list = setup_module_export_list(export_list, atom_tbl)?;
 
         Ok(export_list.into_iter().collect())
     }
@@ -1060,7 +1063,7 @@ impl<'a, LS: LoadState<'a>> Loader<'a, LS> {
 
                 self.payload.clause_clauses.push((head, body));
             }
-            head @ Term::Literal(_, Literal::Atom(..)) | head @ Term::Clause(..) => {
+            head @ (Term::Clause(..) | Term::Literal(_, Literal::Atom(_))) => {
                 let body = Term::Literal(Cell::default(), Literal::Atom(atom!("true")));
                 self.payload.clause_clauses.push((head, body));
             }
@@ -1218,14 +1221,18 @@ impl<'a, LS: LoadState<'a>> Loader<'a, LS> {
          * but to multifile and discontiguous predicates as well.
          */
 
-        let code_index = self.get_or_insert_code_index(key, compilation_target);
+        let offset = self.get_or_insert_code_index(key, compilation_target);
+        let code_idx_ptr = LS::machine_st(&mut self.payload)
+            .arena
+            .code_index_tbl
+            .get_entry(offset.into());
 
-        if code_index.is_undefined() {
+        if code_idx_ptr.is_undefined() {
-            set_code_index(
+            set_code_index::<LS>(
-                &mut self.payload.retraction_info,
+                &mut self.payload,
                 &compilation_target,
                 key,
-                code_index,
+                offset,
                 IndexPtr::dynamic_undefined(),
             );
         }
@@ -1289,13 +1296,16 @@ impl<'a, LS: LoadState<'a>> Loader<'a, LS> {
 
     fn add_clause_clause_if_dynamic(&mut self, term: &Term) -> Result<(), SessionError> {
         if let Some(predicate_name) = ClauseInfo::name(term) {
-            let arity = ClauseInfo::arity(term);
+            let predicate_arity = ClauseInfo::arity(term);
             let predicates_compilation_target = self.payload.predicates.compilation_target;
 
             let is_dynamic = self
                 .wam_prelude
                 .indices
-                .get_predicate_skeleton(&predicates_compilation_target, &(predicate_name, arity))
+                .get_predicate_skeleton(
+                    &predicates_compilation_target,
+                    &(predicate_name, predicate_arity),
+                )
                 .map(|skeleton| skeleton.core.is_dynamic)
                 .unwrap_or(false);
 
@@ -1369,8 +1379,9 @@ impl<'a> MachinePreludeView<'a> {
 impl MachineState {
     pub(super) fn read_term_from_heap(&mut self, term_addr: HeapCellValue) -> Term {
         let mut term_stack = vec![];
+        self.heap[0] = term_addr;
         let mut iter =
-            stackful_post_order_iter::<NonListElider>(&mut self.heap, &mut self.stack, term_addr);
+            stackful_post_order_iter::<NonListElider>(&mut self.heap, &mut self.stack, 0);
 
         while let Some(addr) = iter.next() {
             let addr = unmark_cell_bits!(addr);
@@ -1384,45 +1395,31 @@ impl MachineState {
 
                     match as_partial_string(head, tail) {
                         Ok((string, Some(tail))) => {
-                            term_stack.push(Term::PartialString(Cell::default(), string, tail));
+                            term_stack.push(Term::PartialString(Cell::default(), Rc::new(string), tail));
                         }
                         Ok((string, None)) => {
-                            let atom = AtomTable::build_with(&self.atom_tbl, &string);
+                            term_stack.push(Term::CompleteString(Cell::default(), Rc::new(string)));
-                            term_stack.push(Term::CompleteString(Cell::default(), atom));
                         }
                         Err(cons_term) => term_stack.push(cons_term),
                     }
                 }
+                (HeapCellValueTag::Cons | HeapCellValueTag::Fixnum | HeapCellValueTag::F64Offset) => {
+                    term_stack.push(Term::Literal(Cell::default(), Literal::try_from(addr).unwrap()));
+                }
                 (HeapCellValueTag::StackVar, h) => {
-                    term_stack.push(Term::Var(Cell::default(), VarPtr::from(format!("s_{}", h))));
+                    term_stack.push(Term::Var(Cell::default(), VarPtr::from(format!("s_{h}"))));
                 }
                 (HeapCellValueTag::Var | HeapCellValueTag::AttrVar, h) => {
-                    term_stack.push(Term::Var(Cell::default(), VarPtr::from(format!("_{}", h))));
+                    term_stack.push(Term::Var(Cell::default(), VarPtr::from(format!("_{h}"))));
-                }
-                (HeapCellValueTag::Cons | HeapCellValueTag::CStr | HeapCellValueTag::Fixnum |
-                 HeapCellValueTag::Char | HeapCellValueTag::F64) => {
-                    term_stack.push(Term::Literal(Cell::default(), Literal::try_from(addr).unwrap()));
                 }
                 (HeapCellValueTag::Atom, (name, arity)) => {
                     let h = iter.focus().value() as usize;
                     let mut arity = arity;
+                    let value = iter.heap[h.saturating_sub(1)];
 
-                    if iter.heap.len() > h + arity + 1 {
+                    if let Some(idx) = get_structure_index(value) {
-                        let value = iter.heap[h + arity + 1];
+                        term_stack.push(Term::Literal(Cell::default(), Literal::CodeIndexOffset(idx.into())));
-
+                        arity += 1;
-                        if let Some(idx) = get_structure_index(value) {
-                            // in the second condition, arity == 0,
-                            // meaning idx cannot pertain to this atom
-                            // if it is the direct subterm of a larger
-                            // structure.
-                            if arity > 0 || !iter.direct_subterm_of_str(h) {
-                                term_stack.push(
-                                    Term::Literal(Cell::default(), Literal::CodeIndex(idx))
-                                );
-
-                                arity += 1;
-                            }
-                        }
                     }
 
                     if arity == 0 {
@@ -1435,28 +1432,22 @@ impl MachineState {
                         term_stack.push(Term::Clause(Cell::default(), name, subterms));
                     }
                 }
-                (HeapCellValueTag::PStr, atom) => {
-                    let tail = term_stack.pop().unwrap();
-
-                    if let Term::Literal(_, Literal::Atom(atom!("[]"))) = &tail {
-                        term_stack.push(Term::CompleteString(Cell::default(), atom));
-                    } else {
-                        term_stack.push(Term::PartialString(
-                            Cell::default(),
-                            atom.as_str().to_owned(),
-                            Box::new(tail),
-                        ));
-                    }
-                }
                 (HeapCellValueTag::PStrLoc, h) => {
-                    let atom = cell_as_atom_cell!(iter.heap[h]).get_name();
+                    let HeapStringScan { string, .. } = iter.heap.scan_slice_to_str(h);
                     let tail = term_stack.pop().unwrap();
 
-                    term_stack.push(Term::PartialString(
+                    term_stack.push(if matches!(tail, Term::Literal(_, Literal::Atom(atom!("[]")))) {
-                        Cell::default(),
+                        Term::CompleteString(
-                        atom.as_str().to_owned(),
+                            Cell::default(),
-                        Box::new(tail),
+                            Rc::new(string.to_owned()),
-                    ));
+                        )
+                    } else {
+                        Term::PartialString(
+                            Cell::default(),
+                            Rc::new(string.to_owned()),
+                            Box::new(tail),
+                        )
+                    });
                 }
                 _ => {
                 }
@@ -1605,7 +1596,7 @@ impl Machine {
         let predicate_name = cell_as_atom!(self.deref_register(2));
 
         let arity = self.deref_register(3);
-        let arity = match Number::try_from(arity) {
+        let arity = match Number::try_from((arity, &self.machine_st.arena.f64_tbl)) {
             Ok(Number::Integer(n)) if *n >= Integer::ZERO && *n <= Integer::from(MAX_ARITY) => {
                 let value: usize = (&*n).try_into().unwrap();
                 Ok(value)
@@ -1981,7 +1972,6 @@ impl Machine {
         };
 
         let stub_gen = || functor_stub(key.0, key.1);
-
         let head = self.deref_register(2);
 
         if head.is_var() {
@@ -2017,7 +2007,14 @@ impl Machine {
                     .wam_prelude
                     .indices
                     .get_predicate_code_index(name, arity, module_name)
-                    .map(|code_idx| code_idx.get_tag())
+                    .map(|offset| {
+                        loader
+                            .payload
+                            .machine_st
+                            .arena
+                            .code_index_tbl
+                            .with_entry(offset.into(), |idx| idx.tag())
+                    })
                     .unwrap_or(IndexPtrTag::DynamicUndefined);
 
                 if idx_tag == IndexPtrTag::Index {
@@ -2123,14 +2120,16 @@ impl Machine {
                 .indices
                 .remove_predicate_skeleton(&compilation_target, &key)
                 .map(|skeleton| {
-                    let mut clause_clause_skeleton = loader
+                    let mut clause_clause_skeleton =
-                        .wam_prelude
+                        match loader.wam_prelude.indices.remove_predicate_skeleton(
-                        .indices
-                        .remove_predicate_skeleton(
                             &clause_clause_compilation_target,
                             &(atom!("$clause"), 2),
-                        )
+                        ) {
-                        .unwrap();
+                            Some(skeleton) => skeleton,
+                            None => {
+                                return vec![];
+                            }
+                        };
 
                     let result = skeleton
                         .core
@@ -2160,9 +2159,16 @@ impl Machine {
                 .indices
                 .remove_predicate_skeleton(&compilation_target, &key);
 
-            let mut code_index = loader.get_or_insert_code_index(key, compilation_target);
+            let offset = loader.get_or_insert_code_index(key, compilation_target);
 
-            code_index.set(IndexPtr::undefined());
+            loader
+                .payload
+                .machine_st
+                .arena
+                .code_index_tbl
+                .with_entry_mut(offset.into(), |code_idx| {
+                    *code_idx = IndexPtr::undefined();
+                });
 
             loader.payload.compilation_target = clause_clause_compilation_target;
 
@@ -2192,7 +2198,7 @@ impl Machine {
             .machine_st
             .store(self.machine_st.deref(self.machine_st[temp_v!(3)]));
 
-        let target_pos = match Number::try_from(target_pos) {
+        let target_pos = match Number::try_from((target_pos, &self.machine_st.arena.f64_tbl)) {
             Ok(Number::Integer(n)) => {
                 let value: usize = (&*n).try_into().unwrap();
                 value
@@ -2342,29 +2348,38 @@ impl Machine {
             .get_meta_predicate_spec(predicate_name, arity, &compilation_target)
         {
             Some(meta_specs) => {
-                let term_loc = self.machine_st.heap.len();
+                let term_loc = self.machine_st.heap.cell_len();
 
-                self.machine_st
+                let mut writer = match self.machine_st.heap.reserve(3 + meta_specs.len()) {
-                    .heap
+                    Ok(writer) => writer,
-                    .push(atom_as_cell!(predicate_name, arity));
+                    Err(err_loc) => {
-                self.machine_st
+                        self.machine_st.throw_resource_error(err_loc);
-                    .heap
+                        return;
-                    .extend(meta_specs.iter().map(|meta_spec| match meta_spec {
+                    }
-                        MetaSpec::Minus => atom_as_cell!(atom!("+")),
+                };
-                        MetaSpec::Plus => atom_as_cell!(atom!("-")),
-                        MetaSpec::Either => atom_as_cell!(atom!("?")),
-                        MetaSpec::Colon => atom_as_cell!(atom!(":")),
-                        MetaSpec::RequiresExpansionWithArgument(ref arg_num) => {
-                            fixnum_as_cell!(Fixnum::build_with(*arg_num as i64))
-                        }
-                    }));
 
-                let heap_loc = self.machine_st.heap.len();
+                writer.write_with(|section| {
+                    section.push_cell(atom_as_cell!(predicate_name, arity));
 
-                self.machine_st
+                    for meta_spec in meta_specs.iter() {
-                    .heap
+                        section.push_cell(match meta_spec {
-                    .push(atom_as_cell!(atom!("meta_predicate"), 1));
+                            MetaSpec::Minus => atom_as_cell!(atom!("+")),
-                self.machine_st.heap.push(str_loc_as_cell!(term_loc));
+                            MetaSpec::Plus => atom_as_cell!(atom!("-")),
+                            MetaSpec::Either => atom_as_cell!(atom!("?")),
+                            MetaSpec::Colon => atom_as_cell!(atom!(":")),
+                            MetaSpec::RequiresExpansionWithArgument(ref arg_num) => {
+                                fixnum_as_cell!(/* FIXME this is not safe */ unsafe {
+                                    Fixnum::build_with_unchecked(*arg_num as i64)
+                                })
+                            }
+                        });
+                    }
+
+                    section.push_cell(atom_as_cell!(atom!("meta_predicate"), 1));
+                    section.push_cell(str_loc_as_cell!(term_loc));
+                });
+
+                let heap_loc = self.machine_st.heap.cell_len() - 2;
 
                 unify!(
                     self.machine_st,

src/machine/machine_errors.rs

@@ -5,6 +5,7 @@ use crate::parser::ast::*;
 #[cfg(feature = "ffi")]
 use crate::ffi::FFIError;
 use crate::forms::*;
+use crate::functor_macro::*;
 use crate::machine::heap::*;
 use crate::machine::loader::CompilationTarget;
 use crate::machine::machine_state::*;
@@ -12,20 +13,13 @@ use crate::machine::streams::*;
 use crate::machine::system_calls::BrentAlgState;
 use crate::types::*;
 
-pub type MachineStub = Vec<HeapCellValue>;
+pub type MachineStub = Vec<FunctorElement>;
 pub type MachineStubGen = Box<dyn Fn(&mut MachineState) -> MachineStub>;
 
-#[derive(Debug, Clone, Copy)]
-enum ErrorProvenance {
-    Constructed, // if constructed, offset the addresses.
-    Received,    // otherwise, preserve the addresses.
-}
-
 #[derive(Debug)]
 pub(crate) struct MachineError {
     stub: MachineStub,
     location: Option<(usize, usize)>, // line_num, col_num
-    from: ErrorProvenance,
 }
 
 // from 7.12.2 b) of 13211-1:1995
@@ -50,6 +44,7 @@ pub(crate) enum ValidType {
     //    PredicateIndicator,
     //    Variable
     TcpListener,
+    Process,
 }
 
 impl ValidType {
@@ -73,6 +68,7 @@ impl ValidType {
             //            ValidType::PredicateIndicator => atom!("predicate_indicator"),
             //            ValidType::Variable => atom!("variable")
             ValidType::TcpListener => atom!("tcp_listener"),
+            ValidType::Process => atom!("process"),
         }
     }
 }
@@ -91,45 +87,26 @@ impl TypeError for HeapCellValue {
     fn type_error(self, _machine_st: &mut MachineState, valid_type: ValidType) -> MachineError {
         let stub = functor!(
             atom!("type_error"),
-            [atom(valid_type.as_atom()), cell(self)]
+            [atom_as_cell((valid_type.as_atom())), cell(self)]
         );
 
         MachineError {
             stub,
             location: None,
-            from: ErrorProvenance::Received,
         }
     }
 }
 
 impl TypeError for MachineStub {
-    fn type_error(self, machine_st: &mut MachineState, valid_type: ValidType) -> MachineError {
+    fn type_error(self, _machine_st: &mut MachineState, valid_type: ValidType) -> MachineError {
         let stub = functor!(
             atom!("type_error"),
-            [atom(valid_type.as_atom()), str(machine_st.heap.len(), 0)],
+            [atom_as_cell((valid_type.as_atom())), functor(self)]
-            [self]
         );
 
         MachineError {
             stub,
             location: None,
-            from: ErrorProvenance::Constructed,
-        }
-    }
-}
-
-impl TypeError for FunctorStub {
-    fn type_error(self, machine_st: &mut MachineState, valid_type: ValidType) -> MachineError {
-        let stub = functor!(
-            atom!("type_error"),
-            [atom(valid_type.as_atom()), str(machine_st.heap.len(), 0)],
-            [self]
-        );
-
-        MachineError {
-            stub,
-            location: None,
-            from: ErrorProvenance::Constructed,
         }
     }
 }
@@ -139,15 +116,14 @@ impl TypeError for Number {
         let stub = functor!(
             atom!("type_error"),
             [
-                atom(valid_type.as_atom()),
+                atom_as_cell((valid_type.as_atom())),
-                number(&mut machine_st.arena, self)
+                number(self, (&mut machine_st.arena))
             ]
         );
 
         MachineError {
             stub,
             location: None,
-            from: ErrorProvenance::Received,
         }
     }
 }
@@ -171,16 +147,15 @@ impl PermissionError for Atom {
         let stub = functor!(
             atom!("permission_error"),
             [
-                atom(perm.as_atom()),
+                atom_as_cell((perm.as_atom())),
-                atom(index_atom),
+                atom_as_cell(index_atom),
-                cell(atom_as_cell!(self))
+                atom_as_cell(self)
             ]
         );
 
         MachineError {
             stub,
             location: None,
-            from: ErrorProvenance::Received,
         }
     }
 }
@@ -214,13 +189,16 @@ impl PermissionError for HeapCellValue {
 
         let stub = functor!(
             atom!("permission_error"),
-            [atom(perm.as_atom()), atom(index_atom), cell(cell)]
+            [
+                atom_as_cell((perm.as_atom())),
+                atom_as_cell(index_atom),
+                cell(cell)
+            ]
         );
 
         MachineError {
             stub,
             location: None,
-            from: ErrorProvenance::Received,
         }
     }
 }
@@ -228,24 +206,22 @@ impl PermissionError for HeapCellValue {
 impl PermissionError for MachineStub {
     fn permission_error(
         self,
-        machine_st: &mut MachineState,
+        _machine_st: &mut MachineState,
         index_atom: Atom,
         perm: Permission,
     ) -> MachineError {
         let stub = functor!(
             atom!("permission_error"),
             [
-                atom(perm.as_atom()),
+                atom_as_cell((perm.as_atom())),
-                atom(index_atom),
+                atom_as_cell(index_atom),
-                str(machine_st.heap.len(), 0)
+                functor(self)
-            ],
+            ]
-            [self]
         );
 
         MachineError {
             stub,
             location: None,
-            from: ErrorProvenance::Constructed,
         }
     }
 }
@@ -256,32 +232,14 @@ pub(super) trait DomainError {
 
 impl DomainError for HeapCellValue {
     fn domain_error(self, _machine_st: &mut MachineState, error: DomainErrorType) -> MachineError {
-        let stub = functor!(atom!("domain_error"), [atom(error.as_atom()), cell(self)]);
-
-        MachineError {
-            stub,
-            location: None,
-            from: ErrorProvenance::Received,
-        }
-    }
-}
-
-impl DomainError for FunctorStub {
-    fn domain_error(
-        self,
-        machine_st: &mut MachineState,
-        valid_type: DomainErrorType,
-    ) -> MachineError {
         let stub = functor!(
             atom!("domain_error"),
-            [atom(valid_type.as_atom()), str(machine_st.heap.len(), 0)],
+            [atom_as_cell((error.as_atom())), cell(self)]
-            [self]
         );
 
         MachineError {
             stub,
             location: None,
-            from: ErrorProvenance::Constructed,
         }
     }
 }
@@ -290,26 +248,36 @@ impl DomainError for Number {
     fn domain_error(self, machine_st: &mut MachineState, error: DomainErrorType) -> MachineError {
         let stub = functor!(
             atom!("domain_error"),
-            [atom(error.as_atom()), number(&mut machine_st.arena, self)]
+            [
+                atom_as_cell((error.as_atom())),
+                number(self, (&mut machine_st.arena))
+            ]
         );
 
         MachineError {
             stub,
             location: None,
-            from: ErrorProvenance::Received,
         }
     }
 }
 
-pub(super) type FunctorStub = [HeapCellValue; 3];
+impl DomainError for MachineStub {
+    fn domain_error(self, _machine_st: &mut MachineState, error: DomainErrorType) -> MachineError {
+        let stub = functor!(
+            atom!("domain_error"),
+            [atom_as_cell((error.as_atom())), functor(self)]
+        );
+
+        MachineError {
+            stub,
+            location: None,
+        }
+    }
+}
 
 #[inline(always)]
-pub(super) fn functor_stub(name: Atom, arity: usize) -> FunctorStub {
+pub(super) fn functor_stub(name: Atom, arity: usize) -> MachineStub {
-    [
+    functor!(atom!("/"), [atom_as_cell(name), fixnum(arity)])
-        atom_as_cell!(atom!("/"), 2),
-        atom_as_cell!(name),
-        fixnum_as_cell!(Fixnum::build_with(arity as i64)),
-    ]
 }
 
 impl MachineState {
@@ -320,37 +288,40 @@ impl MachineState {
         MachineError {
             stub,
             location: None,
-            from: ErrorProvenance::Received,
         }
     }
 
     pub(super) fn evaluation_error(&mut self, eval_error: EvalError) -> MachineError {
-        let stub = functor!(atom!("evaluation_error"), [atom(eval_error.as_atom())]);
+        let stub = functor!(
+            atom!("evaluation_error"),
+            [atom_as_cell((eval_error.as_atom()))]
+        );
 
         MachineError {
             stub,
             location: None,
-            from: ErrorProvenance::Received,
         }
     }
 
-    pub(super) fn resource_error(&mut self, err: ResourceError) -> MachineError {
+    pub(super) fn resource_error(err: ResourceError) -> MachineError {
         let stub = match err {
             ResourceError::FiniteMemory(size_requested) => {
                 functor!(
                     atom!("resource_error"),
-                    [atom(atom!("finite_memory")), cell(size_requested)]
+                    [atom_as_cell((atom!("finite_memory"))), cell(size_requested)]
                 )
             }
             ResourceError::OutOfFiles => {
-                functor!(atom!("resource_error"), [atom(atom!("file_descriptors"))])
+                functor!(
+                    atom!("resource_error"),
+                    [atom_as_cell((atom!("file_descriptors")))]
+                )
             }
         };
 
         MachineError {
             stub,
             location: None,
-            from: ErrorProvenance::Received,
         }
     }
 
@@ -367,13 +338,12 @@ impl MachineState {
             ExistenceError::Module(name) => {
                 let stub = functor!(
                     atom!("existence_error"),
-                    [atom(atom!("source_sink")), atom(name)]
+                    [atom_as_cell((atom!("source_sink"))), atom_as_cell(name)]
                 );
 
                 MachineError {
                     stub,
                     location: None,
-                    from: ErrorProvenance::Received,
                 }
             }
             ExistenceError::QualifiedProcedure {
@@ -381,36 +351,30 @@ impl MachineState {
                 name,
                 arity,
             } => {
-                let h = self.heap.len();
+                let ind_stub = functor!(atom!("/"), [atom_as_cell(name), fixnum(arity)]);
-
+                let res_stub = functor!(atom!(":"), [atom_as_cell(module_name), functor(ind_stub)]);
-                let ind_stub = functor!(atom!("/"), [atom(name), fixnum(arity)]);
-                let res_stub = functor!(atom!(":"), [atom(module_name), str(h + 3, 0)], [ind_stub]);
 
                 let stub = functor!(
                     atom!("existence_error"),
-                    [atom(atom!("procedure")), str(h, 0)],
+                    [atom_as_cell((atom!("procedure"))), functor(res_stub)]
-                    [res_stub]
                 );
 
                 MachineError {
                     stub,
                     location: None,
-                    from: ErrorProvenance::Constructed,
                 }
             }
             ExistenceError::Procedure(name, arity) => {
-                let culprit = functor!(atom!("/"), [atom(name), fixnum(arity)]);
+                let culprit = functor!(atom!("/"), [atom_as_cell(name), fixnum(arity)]);
 
                 let stub = functor!(
                     atom!("existence_error"),
-                    [atom(atom!("procedure")), str(self.heap.len(), 0)],
+                    [atom_as_cell((atom!("procedure"))), functor(culprit)]
-                    [culprit]
                 );
 
                 MachineError {
                     stub,
                     location: None,
-                    from: ErrorProvenance::Constructed,
                 }
             }
             ExistenceError::ModuleSource(source) => {
@@ -418,40 +382,83 @@ impl MachineState {
 
                 let stub = functor!(
                     atom!("existence_error"),
-                    [atom(atom!("source_sink")), str(self.heap.len(), 0)],
+                    [atom_as_cell((atom!("source_sink"))), functor(source_stub)]
-                    [source_stub]
                 );
 
                 MachineError {
                     stub,
                     location: None,
-                    from: ErrorProvenance::Constructed,
                 }
             }
             ExistenceError::SourceSink(culprit) => {
                 let stub = functor!(
                     atom!("existence_error"),
-                    [atom(atom!("source_sink")), cell(culprit)]
+                    [atom_as_cell((atom!("source_sink"))), cell(culprit)]
                 );
 
                 MachineError {
                     stub,
                     location: None,
-                    from: ErrorProvenance::Received,
                 }
             }
             ExistenceError::Stream(culprit) => {
                 let stub = functor!(
                     atom!("existence_error"),
-                    [atom(atom!("stream")), cell(culprit)]
+                    [atom_as_cell((atom!("stream"))), cell(culprit)]
                 );
 
                 MachineError {
                     stub,
                     location: None,
-                    from: ErrorProvenance::Received,
                 }
             }
+            ExistenceError::Process(culprit) => {
+                let stub = functor!(
+                    atom!("existence_error"),
+                    [atom_as_cell((atom!("process"))), cell(culprit)]
+                );
+
+                MachineError {
+                    stub,
+                    location: None,
+                }
+            }
+        }
+    }
+
+    pub(crate) fn directive_error(&mut self, err: DirectiveError) -> MachineError {
+        match err {
+            DirectiveError::ExpectedDirective(_term) => self.domain_error(
+                DomainErrorType::Directive,
+                atom_as_cell!(atom!("todo_insert_invalid_term_here")),
+            ),
+            DirectiveError::InvalidDirective(name, arity) => {
+                self.domain_error(DomainErrorType::Directive, functor_stub(name, arity))
+            }
+            DirectiveError::InvalidOpDeclNameType(_term) => self.type_error(
+                ValidType::List,
+                atom_as_cell!(atom!("todo_insert_invalid_term_here")),
+            ),
+            DirectiveError::InvalidOpDeclSpecDomain(_term) => self.domain_error(
+                DomainErrorType::OperatorSpecifier,
+                atom_as_cell!(atom!("todo_insert_invalid_term_here")),
+            ),
+            DirectiveError::InvalidOpDeclSpecValue(atom) => {
+                self.domain_error(DomainErrorType::OperatorSpecifier, atom_as_cell!(atom))
+            }
+            DirectiveError::InvalidOpDeclPrecType(_term) => self.type_error(
+                ValidType::Integer,
+                atom_as_cell!(atom!("todo_insert_invalid_term_here")),
+            ),
+            DirectiveError::InvalidOpDeclPrecDomain(num) => {
+                self.domain_error(DomainErrorType::OperatorPriority, fixnum_as_cell!(num))
+            }
+            DirectiveError::ShallNotCreate(atom) => {
+                self.permission_error(Permission::Create, atom!("operator"), atom)
+            }
+            DirectiveError::ShallNotModify(atom) => {
+                self.permission_error(Permission::Modify, atom!("operator"), atom)
+            }
         }
     }
 
@@ -471,12 +478,11 @@ impl MachineState {
 
     fn arithmetic_error(&mut self, err: ArithmeticError) -> MachineError {
         match err {
-            ArithmeticError::UninstantiatedVar => self.instantiation_error(),
+            ArithmeticError::NonEvaluableFunctor(cell, arity) => {
-            ArithmeticError::NonEvaluableFunctor(literal, arity) => {
+                let culprit = functor!(atom!("/"), [literal(cell), fixnum(arity)]);
-                let culprit = functor!(atom!("/"), [literal(literal), fixnum(arity)]);
-
                 self.type_error(ValidType::Evaluable, culprit)
             }
+            ArithmeticError::UninstantiatedVar => self.instantiation_error(),
         }
     }
 
@@ -495,7 +501,6 @@ impl MachineState {
         MachineError {
             stub,
             location: None,
-            from: ErrorProvenance::Received,
         }
     }
 
@@ -504,16 +509,12 @@ impl MachineState {
             SessionError::CannotOverwriteBuiltIn(key) => self.permission_error(
                 Permission::Modify,
                 atom!("static_procedure"),
-                functor_stub(key.0, key.1)
+                functor_stub(key.0, key.1),
-                    .into_iter()
-                    .collect::<MachineStub>(),
             ),
             SessionError::CannotOverwriteStaticProcedure(key) => self.permission_error(
                 Permission::Modify,
                 atom!("static_procedure"),
-                functor_stub(key.0, key.1)
+                functor_stub(key.0, key.1),
-                    .into_iter()
-                    .collect::<MachineStub>(),
             ),
             SessionError::CannotOverwriteBuiltInModule(module) => {
                 self.permission_error(Permission::Modify, atom!("static_module"), module)
@@ -524,8 +525,7 @@ impl MachineState {
 
                 let stub = functor!(
                     atom!("module_does_not_contain_claimed_export"),
-                    [atom(module_name), str(self.heap.len() + 4, 0)],
+                    [atom_as_cell(module_name), functor(functor_stub)]
-                    [functor_stub]
                 );
 
                 self.permission_error(Permission::Access, atom!("private_procedure"), stub)
@@ -536,7 +536,7 @@ impl MachineState {
                 self.permission_error(
                     Permission::Modify,
                     atom!("module"),
-                    functor!(error_atom, [atom(module_name)]),
+                    functor!(error_atom, [atom_as_cell(module_name)]),
                 )
             }
             SessionError::NamelessEntry => {
@@ -555,15 +555,12 @@ impl MachineState {
             }
             SessionError::CompilationError(err) => self.syntax_error(err),
             SessionError::PredicateNotMultifileOrDiscontiguous(compilation_target, key) => {
-                let functor_stub = functor_stub(key.0, key.1);
-
                 let stub = functor!(
                     atom!(":"),
                     [
-                        atom(compilation_target.module_name()),
+                        atom_as_cell((compilation_target.module_name())),
-                        str(self.heap.len() + 4, 0)
+                        functor((key.0), [fixnum((key.1))])
-                    ],
+                    ]
-                    [functor_stub]
                 );
 
                 self.permission_error(
@@ -587,30 +584,36 @@ impl MachineState {
         }
 
         let location = err.line_and_col_num();
-        let len = self.heap.len();
         let stub = err.as_functor();
 
-        let stub = functor!(atom!("syntax_error"), [str(len, 0)], [stub]);
+        let stub = functor!(atom!("syntax_error"), [functor(stub)]);
 
-        MachineError {
+        MachineError { stub, location }
-            stub,
-            location,
-            from: ErrorProvenance::Constructed,
-        }
     }
 
-    pub(super) fn representation_error(&mut self, flag: RepFlag) -> MachineError {
+    pub(super) fn representation_error(&self, flag: RepFlag) -> MachineError {
-        let stub = functor!(atom!("representation_error"), [atom(flag.as_atom())]);
+        let stub = functor!(
+            atom!("representation_error"),
+            [atom_as_cell((flag.as_atom()))]
+        );
+
+        MachineError {
+            stub,
+            location: None,
+        }
+    }
+
+    pub(super) fn unreachable_error(&self) -> MachineError {
+        let stub = functor!(atom!("system_error"));
 
         MachineError {
             stub,
             location: None,
-            from: ErrorProvenance::Received,
         }
     }
 
     #[cfg(feature = "ffi")]
-    pub(super) fn ffi_error(&mut self, err: FFIError) -> MachineError {
+    pub(super) fn ffi_error(&self, err: FFIError) -> MachineError {
         let error_atom = match err {
             FFIError::ValueCast => atom!("value_cast"),
             FFIError::ValueDontFit => atom!("value_dont_fit"),
@@ -619,62 +622,50 @@ impl MachineState {
             FFIError::FunctionNotFound => atom!("function_not_found"),
             FFIError::StructNotFound => atom!("struct_not_found"),
         };
-        let stub = functor!(atom!("ffi_error"), [atom(error_atom)]);
+        let stub = functor!(atom!("ffi_error"), [atom_as_cell(error_atom)]);
 
         MachineError {
             stub,
             location: None,
-            from: ErrorProvenance::Constructed,
         }
     }
 
-    pub(super) fn error_form(&mut self, err: MachineError, src: FunctorStub) -> MachineStub {
+    pub(super) fn error_form(&mut self, err: MachineError, src: MachineStub) -> MachineStub {
-        let h = self.heap.len();
+        if let Some((line_num, _col_num)) = err.location {
-        let location = err.location;
+            functor!(
-        let stub_addition_len = if err.len() == 1 {
+                atom!("error"),
-            0 // if err contains 1 cell, it can be inlined at stub[1].
+                [
+                    functor((err.stub)),
+                    functor(
+                        (atom!(":")),
+                        [functor(src), number(line_num, (&mut self.arena))]
+                    )
+                ]
+            )
         } else {
-            err.len()
+            functor!(atom!("error"), [functor((err.stub)), functor(src)])
-        };
-
-        let mut stub = vec![
-            atom_as_cell!(atom!("error"), 2),
-            str_loc_as_cell!(h + 3),
-            str_loc_as_cell!(h + 3 + stub_addition_len),
-        ];
-
-        if stub_addition_len > 0 {
-            stub.extend(err.into_iter(3));
-        } else {
-            stub[1] = err.stub[0];
         }
+    }
 
-        if let Some((line_num, _)) = location {
+    // throw an error pre-allocated in the heap
-            stub.push(atom_as_cell!(atom!(":"), 2));
+    pub(super) fn throw_resource_error(&mut self, err_loc: usize) {
-            stub.push(str_loc_as_cell!(h + 6 + stub_addition_len));
+        self.registers[1] = str_loc_as_cell!(err_loc);
-            stub.push(integer_as_cell!(Number::arena_from(
+        self.set_ball();
-                line_num,
+        self.unwind_stack();
-                &mut self.arena
-            )));
-        }
-
-        stub.extend(src.iter());
-        stub
     }
 
     pub(super) fn throw_exception(&mut self, err: MachineStub) {
-        let h = self.heap.len();
-        let err_len = err.len();
-
         self.ball.boundary = 0;
         self.ball.stub.truncate(0);
 
-        self.heap.extend(err);
+        let mut writer = Heap::functor_writer(err);
 
-        self.registers[1] = if err_len == 1 {
+        self.registers[1] = match writer(&mut self.heap) {
-            heap_loc_as_cell!(h)
+            Ok(loc) => loc,
-        } else {
+            Err(resource_err_loc) => {
-            str_loc_as_cell!(h)
+                self.throw_resource_error(resource_err_loc);
+                return;
+            }
         };
 
         self.set_ball();
@@ -682,21 +673,6 @@ impl MachineState {
     }
 }
 
-impl MachineError {
-    fn into_iter(self, offset: usize) -> Box<dyn Iterator<Item = HeapCellValue>> {
-        match self.from {
-            ErrorProvenance::Constructed => {
-                Box::new(self.stub.into_iter().map(move |hcv| hcv + offset))
-            }
-            ErrorProvenance::Received => Box::new(self.stub.into_iter()),
-        }
-    }
-
-    fn len(&self) -> usize {
-        self.stub.len()
-    }
-}
-
 #[derive(Debug)]
 pub enum CompilationError {
     Arithmetic(ArithmeticError),
@@ -711,6 +687,7 @@ pub enum CompilationError {
     InvalidRuleHead,
     InvalidUseModuleDecl,
     InvalidModuleResolution(Atom),
+    FiniteMemoryInHeap(usize),
 }
 
 #[derive(Debug)]
@@ -757,11 +734,9 @@ impl CompilationError {
                 functor!(atom!("exceeded_max_arity"))
             }
             CompilationError::InadmissibleFact => {
-                // TODO: type_error(callable, _).
                 functor!(atom!("inadmissible_fact"))
             }
             CompilationError::InadmissibleQueryTerm => {
-                // TODO: type_error(callable, _).
                 functor!(atom!("inadmissible_query_term"))
             }
             CompilationError::InvalidDirective(_) => {
@@ -776,8 +751,8 @@ impl CompilationError {
             CompilationError::InvalidModuleExport => {
                 functor!(atom!("invalid_module_export"))
             }
-            CompilationError::InvalidModuleResolution(ref module_name) => {
+            &CompilationError::InvalidModuleResolution(module_name) => {
-                functor!(atom!("no_such_module"), [atom(module_name)])
+                functor!(atom!("no_such_module"), [atom_as_cell(module_name)])
             }
             CompilationError::InvalidRuleHead => {
                 functor!(atom!("invalid_head_of_rule")) // TODO: type_error(callable, _).
@@ -788,6 +763,9 @@ impl CompilationError {
             CompilationError::ParserError(ref err) => {
                 functor!(err.as_atom())
             }
+            CompilationError::FiniteMemoryInHeap(h) => {
+                vec![FunctorElement::AbsoluteCell(str_loc_as_cell!(*h))]
+            }
         }
     }
 }
@@ -896,14 +874,29 @@ impl EvalError {
 // used by '$skip_max_list'.
 #[derive(Debug, Clone, Copy, PartialEq, Eq)]
 pub enum CycleSearchResult {
-    Cyclic(usize),
+    Cyclic {
+        lambda: usize,
+    }, // number of steps
     EmptyList,
-    NotList(usize, HeapCellValue), // the list length until the second argument in the heap
+    NotList {
-    PartialList(usize, Ref),       // the list length (up to max), and an offset into the heap.
+        num_steps: usize,
-    ProperList(usize),             // the list length.
+        heap_loc: HeapCellValue,
-    PStrLocation(usize, usize, usize), // list length (up to max), the heap address of the PStr, the offset
+    },
-    UntouchedList(usize, usize), // list length (up to max), the address of an uniterated Addr::Lis(address).
+    PartialList {
-    UntouchedCStr(Atom, usize),
+        num_steps: usize,
+        heap_loc: HeapCellValue,
+    },
+    ProperList {
+        num_steps: usize,
+    },
+    PStrLocation {
+        num_steps: usize,
+        pstr_loc: HeapCellValue,
+    },
+    UntouchedList {
+        num_steps: usize,
+        list_loc: usize,
+    },
 }
 
 impl MachineState {
@@ -915,11 +908,11 @@ impl MachineState {
         let sorted = self.store(self.deref(self.registers[2]));
 
         match BrentAlgState::detect_cycles(&self.heap, list) {
-            CycleSearchResult::PartialList(..) => {
+            CycleSearchResult::PartialList { .. } => {
                 let err = self.instantiation_error();
                 return Err(self.error_form(err, stub_gen()));
             }
-            CycleSearchResult::NotList(..) | CycleSearchResult::Cyclic(_) => {
+            CycleSearchResult::NotList { .. } | CycleSearchResult::Cyclic { .. } => {
                 let err = self.type_error(ValidType::List, list);
                 return Err(self.error_form(err, stub_gen()));
             }
@@ -927,7 +920,9 @@ impl MachineState {
         };
 
         match BrentAlgState::detect_cycles(&self.heap, sorted) {
-            CycleSearchResult::NotList(..) | CycleSearchResult::Cyclic(_) if !sorted.is_var() => {
+            CycleSearchResult::NotList { .. } | CycleSearchResult::Cyclic { .. }
+                if !sorted.is_var() =>
+            {
                 let err = self.type_error(ValidType::List, sorted);
                 Err(self.error_form(err, stub_gen()))
             }
@@ -939,7 +934,9 @@ impl MachineState {
         let stub_gen = || functor_stub(atom!("keysort"), 2);
 
         match BrentAlgState::detect_cycles(&self.heap, list) {
-            CycleSearchResult::NotList(..) | CycleSearchResult::Cyclic(_) if !list.is_var() => {
+            CycleSearchResult::NotList { .. } | CycleSearchResult::Cyclic { .. }
+                if !list.is_var() =>
+            {
                 let err = self.type_error(ValidType::List, list);
                 Err(self.error_form(err, stub_gen()))
             }
@@ -1001,11 +998,11 @@ impl MachineState {
         let sorted = self.store(self.deref(self[temp_v!(2)]));
 
         match BrentAlgState::detect_cycles(&self.heap, pairs) {
-            CycleSearchResult::PartialList(..) => {
+            CycleSearchResult::PartialList { .. } => {
                 let err = self.instantiation_error();
                 Err(self.error_form(err, stub_gen()))
             }
-            CycleSearchResult::NotList(..) | CycleSearchResult::Cyclic(_) => {
+            CycleSearchResult::NotList { .. } | CycleSearchResult::Cyclic { .. } => {
                 let err = self.type_error(ValidType::List, pairs);
                 Err(self.error_form(err, stub_gen()))
             }
@@ -1028,6 +1025,7 @@ pub enum ExistenceError {
     },
     SourceSink(HeapCellValue),
     Stream(HeapCellValue),
+    Process(HeapCellValue),
 }
 
 #[derive(Debug)]

src/machine/machine_indices.rs

@@ -2,7 +2,6 @@
 
 use crate::parser::ast::*;
 
-use crate::arena::*;
 use crate::atom_table::*;
 use crate::forms::*;
 use crate::machine::loader::*;
@@ -10,6 +9,7 @@ use crate::machine::machine_state::*;
 use crate::machine::streams::{Stream, StreamOptions};
 use crate::machine::ClauseType;
 use crate::machine::MachineStubGen;
+use crate::offset_table::*;
 
 use fxhash::FxBuildHasher;
 use indexmap::{IndexMap, IndexSet};
@@ -18,7 +18,6 @@ use scryer_modular_bitfield::{bitfield, BitfieldSpecifier};
 
 use std::cmp::Ordering;
 use std::collections::BTreeSet;
-use std::ops::{Deref, DerefMut};
 
 use crate::types::*;
 
@@ -126,10 +125,19 @@ impl IndexPtr {
     pub(crate) fn is_dynamic_undefined(&self) -> bool {
         matches!(self.tag(), IndexPtrTag::DynamicUndefined)
     }
+
+    #[inline]
+    pub(crate) fn local(&self) -> Option<usize> {
+        match self.tag() {
+            IndexPtrTag::Index => Some(self.p() as usize),
+            IndexPtrTag::DynamicIndex => Some(self.p() as usize),
+            _ => None,
+        }
+    }
 }
 
-#[derive(Debug, Clone, Copy, Ord, Hash, PartialOrd, Eq, PartialEq)]
+#[derive(Debug, Clone, Copy)] // , Ord, Hash, PartialOrd, Eq, PartialEq)]
-pub struct CodeIndex(TypedArenaPtr<IndexPtr>);
+pub struct CodeIndex(CodeIndexOffset);
 
 #[cfg(target_pointer_width = "32")]
 const_assert!(std::mem::align_of::<CodeIndex>() == 4);
@@ -137,78 +145,53 @@ const_assert!(std::mem::align_of::<CodeIndex>() == 4);
 #[cfg(target_pointer_width = "64")]
 const_assert!(std::mem::align_of::<CodeIndex>() == 8);
 
-impl Deref for CodeIndex {
+impl From<CodeIndex> for HeapCellValue {
-    type Target = TypedArenaPtr<IndexPtr>;
-
     #[inline(always)]
-    fn deref(&self) -> &TypedArenaPtr<IndexPtr> {
+    fn from(idx: CodeIndex) -> HeapCellValue {
-        &self.0
+        HeapCellValue::from(idx.0)
     }
 }
 
-impl DerefMut for CodeIndex {
+impl From<CodeIndexOffset> for CodeIndex {
     #[inline(always)]
-    fn deref_mut(&mut self) -> &mut TypedArenaPtr<IndexPtr> {
+    fn from(offset: CodeIndexOffset) -> CodeIndex {
-        &mut self.0
+        CodeIndex(offset)
     }
 }
 
-impl From<CodeIndex> for UntypedArenaPtr {
+impl From<CodeIndex> for CodeIndexOffset {
     #[inline(always)]
-    fn from(ptr: CodeIndex) -> UntypedArenaPtr {
+    fn from(value: CodeIndex) -> CodeIndexOffset {
-        UntypedArenaPtr::build_with(ptr.0.as_ptr() as usize)
+        value.0
     }
 }
 
-impl From<TypedArenaPtr<IndexPtr>> for CodeIndex {
+impl From<&'_ CodeIndex> for CodeIndexOffset {
     #[inline(always)]
-    fn from(ptr: TypedArenaPtr<IndexPtr>) -> CodeIndex {
+    fn from(value: &'_ CodeIndex) -> CodeIndexOffset {
-        CodeIndex(ptr)
+        value.0
     }
 }
 
 impl CodeIndex {
     #[inline]
-    pub(crate) fn new(ptr: IndexPtr, arena: &mut Arena) -> Self {
+    pub(crate) fn new(ptr: IndexPtr, code_index_tbl: &mut CodeIndexTable) -> Self {
-        CodeIndex(arena_alloc!(ptr, arena))
+        CodeIndex(code_index_tbl.build_with(ptr))
     }
 
     #[inline(always)]
-    pub(crate) fn default(arena: &mut Arena) -> Self {
+    pub(crate) fn default(code_index_tbl: &mut CodeIndexTable) -> Self {
-        CodeIndex::new(IndexPtr::undefined(), arena)
+        CodeIndex::new(IndexPtr::undefined(), code_index_tbl)
-    }
-
-    pub(crate) fn local(&self) -> Option<usize> {
-        match self.0.tag() {
-            IndexPtrTag::Index => Some(self.0.p() as usize),
-            IndexPtrTag::DynamicIndex => Some(self.0.p() as usize),
-            _ => None,
-        }
     }
 
     #[inline(always)]
-    pub(crate) fn get(&self) -> IndexPtr {
+    pub(crate) fn set(&self, code_index_tbl: &mut CodeIndexTable, value: IndexPtr) {
-        *self.0.deref()
+        code_index_tbl.with_entry_mut(self.0, |idx| *idx = value);
     }
 
     #[inline(always)]
-    pub(crate) fn set(&mut self, value: IndexPtr) {
+    pub(crate) fn replace(&self, code_index_tbl: &mut CodeIndexTable, value: IndexPtr) -> IndexPtr {
-        *self.0.deref_mut() = value;
+        code_index_tbl.with_entry_mut(self.0, |idx| std::mem::replace(idx, value))
-    }
-
-    #[inline(always)]
-    pub(crate) fn get_tag(self) -> IndexPtrTag {
-        self.0.tag()
-    }
-
-    #[inline(always)]
-    pub(crate) fn replace(&mut self, value: IndexPtr) -> IndexPtr {
-        std::mem::replace(self.0.deref_mut(), value)
-    }
-
-    #[inline(always)]
-    pub(crate) fn as_ptr(&self) -> *const IndexPtr {
-        self.0.as_ptr()
     }
 }
 
@@ -223,7 +206,7 @@ impl VarKey {
     #[inline]
     pub(crate) fn to_string(&self) -> String {
         match self {
-            VarKey::AnonVar(h) => format!("_{}", h),
+            VarKey::AnonVar(h) => format!("_{h}"),
             VarKey::VarPtr(var) => var.borrow().to_string(),
         }
     }
@@ -543,7 +526,7 @@ impl IndexStore {
         &'a self,
         range: R,
     ) -> impl Iterator<Item = Stream> + 'a {
-        self.streams.range(range).into_iter().copied()
+        self.streams.range(range).copied()
     }
 
     /// Forcibly sets `alias` to `stream`.

src/machine/machine_state.rs

@@ -1,6 +1,7 @@
 use crate::arena::*;
 use crate::atom_table::*;
 use crate::forms::*;
+use crate::functor_macro::*;
 use crate::heap_iter::*;
 use crate::heap_print::*;
 use crate::machine::attributed_variables::*;
@@ -21,7 +22,7 @@ use indexmap::IndexMap;
 
 use std::convert::TryFrom;
 use std::fmt;
-use std::ops::{Index, IndexMut};
+use std::ops::{Index, IndexMut, Range};
 use std::sync::Arc;
 
 pub(crate) type Registers = [HeapCellValue; MAX_ARITY + 1];
@@ -35,8 +36,8 @@ pub(super) enum MachineMode {
 #[derive(Debug, Clone)]
 pub(super) enum HeapPtr {
     HeapCell(usize),
-    PStrChar(usize, usize),
+    PStr(usize), // Char(usize),
-    PStrLocation(usize, usize),
+                 // PStrLocation(usize),
 }
 
 impl Default for HeapPtr {
@@ -183,47 +184,62 @@ impl IndexMut<RegType> for MachineState {
     }
 }
 
-pub type CallResult = Result<(), Vec<HeapCellValue>>;
+pub type CallResult = Result<(), Vec<FunctorElement>>;
-
-#[inline(always)]
-pub fn pstr_loc_and_offset(heap: &[HeapCellValue], index: usize) -> (usize, Fixnum) {
-    read_heap_cell!(heap[index],
-        (HeapCellValueTag::PStr | HeapCellValueTag::CStr) => {
-            (index, Fixnum::build_with(0))
-        }
-        (HeapCellValueTag::PStrOffset, h) => {
-            (h, cell_as_fixnum!(heap[index+1]))
-        }
-        _ => {
-            unreachable!()
-        }
-    )
-}
 
+// size may be an upper bound.
+// true_size is calculated to compute the exact offset.
 fn push_var_eq_functors<'a>(
     heap: &mut Heap,
+    size: usize,
     iter: impl Iterator<Item = (&'a VarKey, &'a HeapCellValue)>,
     atom_tbl: &AtomTable,
-) -> Vec<HeapCellValue> {
+) -> Result<HeapCellValue, usize> {
-    let mut list_of_var_eqs = vec![];
+    let src_h = heap.cell_len();
 
-    for (var, binding) in iter {
+    let true_size = if size > 0 {
-        let var_atom = AtomTable::build_with(atom_tbl, &var.to_string());
+        let mut writer = heap.reserve(2 + 5 * size)?;
-        let h = heap.len();
 
-        heap.push(atom_as_cell!(atom!("="), 2));
+        writer
-        heap.push(atom_as_cell!(var_atom));
+            .write_with(|section| {
-        heap.push(*binding);
+                let mut size = 0;
 
-        list_of_var_eqs.push(str_loc_as_cell!(h));
+                for (var, binding) in iter {
-    }
+                    let var_atom = AtomTable::build_with(atom_tbl, &var.to_string());
 
-    list_of_var_eqs
+                    section.push_cell(atom_as_cell!(atom!("="), 2));
+                    section.push_cell(atom_as_cell!(var_atom));
+                    section.push_cell(*binding);
+
+                    size += 1;
+                }
+
+                for idx in 0..size {
+                    section.push_cell(list_loc_as_cell!(section.cell_len() + 1));
+                    section.push_cell(str_loc_as_cell!(src_h + 3 * idx));
+                }
+
+                if size > 0 {
+                    section.push_cell(empty_list_as_cell!());
+                }
+
+                size
+            })
+            .result
+    } else {
+        size
+    };
+
+    Ok(if true_size > 0 {
+        heap_loc_as_cell!(src_h + 3 * true_size)
+    } else {
+        empty_list_as_cell!()
+    })
 }
 
 #[derive(Debug)]
 pub struct Ball {
     pub(super) boundary: usize,
+    pub(super) pstr_boundary: usize,
     pub(super) stub: Heap,
 }
 
@@ -231,23 +247,44 @@ impl Ball {
     pub(super) fn new() -> Self {
         Ball {
             boundary: 0,
+            pstr_boundary: 0,
             stub: Heap::new(),
         }
     }
 
     pub(super) fn reset(&mut self) {
         self.boundary = 0;
+        self.pstr_boundary = 0;
         self.stub.clear();
     }
 
-    pub(super) fn copy_and_align(&self, h: usize) -> Heap {
+    pub(super) fn copy_and_align_to(&self, dest: &mut Heap) -> Result<usize, usize> {
+        let h = dest.cell_len();
         let diff = self.boundary as i64 - h as i64;
 
-        self.stub
+        let mut dest_writer = dest.reserve(self.stub.cell_len())?;
-            .iter()
+
-            .cloned()
+        dest_writer.write_with(|section| {
-            .map(|heap_value| heap_value - diff)
+            for idx in 0..self.pstr_boundary {
-            .collect()
+                section.push_cell(self.stub[idx] - diff);
+            }
+        });
+
+        let mut pstr_threshold = heap_index!(self.pstr_boundary);
+
+        while pstr_threshold < heap_index!(self.stub.cell_len()) {
+            let HeapStringScan { string, tail_idx } = self.stub.scan_slice_to_str(pstr_threshold);
+
+            pstr_threshold += dest_writer
+                .write_with(|section| {
+                    if section.push_pstr(string).is_some() {
+                        section.push_cell(self.stub[tail_idx] - diff);
+                    }
+                })
+                .bytes_written;
+        }
+
+        Ok(h)
     }
 }
 
@@ -279,21 +316,6 @@ impl<'a> IndexMut<usize> for CopyTerm<'a> {
 }
 
 impl<'a> CopierTarget for CopyTerm<'a> {
-    #[inline(always)]
-    fn threshold(&self) -> usize {
-        self.state.heap.len()
-    }
-
-    #[inline(always)]
-    fn push(&mut self, hcv: HeapCellValue) {
-        self.state.heap.push(hcv);
-    }
-
-    #[inline(always)]
-    fn push_attr_var_queue(&mut self, attr_var_loc: usize) {
-        self.state.attr_var_init.attr_var_queue.push(attr_var_loc);
-    }
-
     #[inline(always)]
     fn store(&self, value: HeapCellValue) -> HeapCellValue {
         self.state.store(value)
@@ -304,10 +326,40 @@ impl<'a> CopierTarget for CopyTerm<'a> {
         self.state.deref(value)
     }
 
+    #[inline(always)]
+    fn push_attr_var_queue(&mut self, attr_var_loc: usize) {
+        self.state.attr_var_init.attr_var_queue.push(attr_var_loc);
+    }
+
     #[inline(always)]
     fn stack(&mut self) -> &mut Stack {
         &mut self.state.stack
     }
+
+    #[inline(always)]
+    fn threshold(&self) -> usize {
+        self.state.heap.cell_len()
+    }
+
+    #[inline(always)]
+    fn as_slice_from<'b>(&'b self, from: usize) -> Box<dyn Iterator<Item = u8> + 'b> {
+        Box::new(self.state.heap.as_slice()[from..].iter().cloned())
+    }
+
+    #[inline(always)]
+    fn copy_pstr_to_threshold(&mut self, pstr_loc: usize) -> Result<usize, usize> {
+        self.state.heap.copy_pstr_within(pstr_loc)
+    }
+
+    #[inline(always)]
+    fn reserve(&mut self, num_cells: usize) -> Result<HeapWriter, usize> {
+        self.state.heap.reserve(num_cells)
+    }
+
+    #[inline(always)]
+    fn copy_slice_to_end(&mut self, bounds: Range<usize>) -> Result<(), usize> {
+        self.state.heap.copy_slice_to_end(bounds)
+    }
 }
 
 #[derive(Debug)]
@@ -315,7 +367,6 @@ pub(super) struct CopyBallTerm<'a> {
     attr_var_queue: &'a mut Vec<usize>,
     stack: &'a mut Stack,
     heap: &'a mut Heap,
-    heap_boundary: usize,
     stub: &'a mut Heap,
 }
 
@@ -326,13 +377,10 @@ impl<'a> CopyBallTerm<'a> {
         heap: &'a mut Heap,
         stub: &'a mut Heap,
     ) -> Self {
-        let hb = heap.len();
-
         CopyBallTerm {
             attr_var_queue,
             stack,
             heap,
-            heap_boundary: hb,
             stub,
         }
     }
@@ -342,10 +390,10 @@ impl<'a> Index<usize> for CopyBallTerm<'a> {
     type Output = HeapCellValue;
 
     fn index(&self, index: usize) -> &Self::Output {
-        if index < self.heap_boundary {
+        if index < self.heap.cell_len() {
             &self.heap[index]
         } else {
-            let index = index - self.heap_boundary;
+            let index = index - self.heap.cell_len();
             &self.stub[index]
         }
     }
@@ -353,10 +401,10 @@ impl<'a> Index<usize> for CopyBallTerm<'a> {
 
 impl<'a> IndexMut<usize> for CopyBallTerm<'a> {
     fn index_mut(&mut self, index: usize) -> &mut Self::Output {
-        if index < self.heap_boundary {
+        if index < self.heap.cell_len() {
             &mut self.heap[index]
         } else {
-            let index = index - self.heap_boundary;
+            let index = index - self.heap.cell_len();
             &mut self.stub[index]
         }
     }
@@ -364,11 +412,7 @@ impl<'a> IndexMut<usize> for CopyBallTerm<'a> {
 
 impl<'a> CopierTarget for CopyBallTerm<'a> {
     fn threshold(&self) -> usize {
-        self.heap_boundary + self.stub.len()
+        self.heap.cell_len() + self.stub.cell_len()
-    }
-
-    fn push(&mut self, value: HeapCellValue) {
-        self.stub.push(value);
     }
 
     #[inline(always)]
@@ -379,10 +423,10 @@ impl<'a> CopierTarget for CopyBallTerm<'a> {
     fn store(&self, value: HeapCellValue) -> HeapCellValue {
         read_heap_cell!(value,
             (HeapCellValueTag::Var | HeapCellValueTag::AttrVar, h) => {
-                if h < self.heap_boundary {
+                if h < self.heap.cell_len() {
                     self.heap[h]
                 } else {
-                    let index = h - self.heap_boundary;
+                    let index = h - self.heap.cell_len();
                     self.stub[index]
                 }
             }
@@ -411,6 +455,45 @@ impl<'a> CopierTarget for CopyBallTerm<'a> {
     fn stack(&mut self) -> &mut Stack {
         self.stack
     }
+
+    fn copy_pstr_to_threshold(&mut self, pstr_loc: usize) -> Result<usize, usize> {
+        debug_assert!(pstr_loc < self.heap.byte_len());
+
+        let HeapStringScan { string, tail_idx } = self.heap.scan_slice_to_str(pstr_loc);
+        self.stub.allocate_pstr(string)?;
+        Ok(tail_idx)
+    }
+
+    fn as_slice_from<'b>(&'b self, from: usize) -> Box<dyn Iterator<Item = u8> + 'b> {
+        if from < self.heap.byte_len() {
+            Box::new(
+                self.heap.as_slice()[from..]
+                    .iter()
+                    .cloned()
+                    .chain(self.stub.as_slice().iter().cloned()),
+            )
+        } else {
+            Box::new(self.stub.as_slice()[from..].iter().cloned())
+        }
+    }
+
+    #[inline]
+    fn reserve(&mut self, num_cells: usize) -> Result<HeapWriter, usize> {
+        self.stub.reserve(num_cells)
+    }
+
+    fn copy_slice_to_end(&mut self, bounds: Range<usize>) -> Result<(), usize> {
+        let len = bounds.end - bounds.start;
+        let mut stub_writer = self.stub.reserve(len)?;
+
+        stub_writer.write_with(|section| {
+            for idx in bounds {
+                section.push_cell(self.heap[idx]);
+            }
+        });
+
+        Ok(())
+    }
 }
 
 impl MachineState {
@@ -461,10 +544,6 @@ impl MachineState {
             let addr = self.store(self.deref(addr));
 
             read_heap_cell!(addr,
-                (HeapCellValueTag::Char, c) => {
-                    chars.push(c);
-                    continue;
-                }
                 (HeapCellValueTag::Atom, (name, arity)) => {
                     if arity == 0 {
                         if let Some(c) = name.as_char() {
@@ -537,39 +616,26 @@ impl MachineState {
     pub fn write_read_term_options(
         &mut self,
         mut var_list: Vec<(VarKey, HeapCellValue, usize)>,
-        singleton_var_list: Vec<HeapCellValue>,
+        singleton_heap_list: HeapCellValue,
     ) -> CallResult {
         var_list.sort_by(|(_, _, idx_1), (_, _, idx_2)| idx_1.cmp(idx_2));
 
-        let list_of_var_eqs = push_var_eq_functors(
-            &mut self.heap,
-            var_list.iter().filter_map(|(var_name, var, _)| {
-                if var_name.is_anon() {
-                    None
-                } else {
-                    Some((var_name, var))
-                }
-            }),
-            &self.atom_tbl,
-        );
-
         let singleton_addr = self.registers[3];
-        let singletons_offset = heap_loc_as_cell!(iter_to_heap_list(
+        unify_fn!(*self, singleton_heap_list, singleton_addr);
-            &mut self.heap,
-            singleton_var_list.into_iter()
-        ));
-
-        unify_fn!(*self, singletons_offset, singleton_addr);
 
         if self.fail {
             return Ok(());
         }
 
         let vars_addr = self.registers[4];
-        let vars_offset = heap_loc_as_cell!(iter_to_heap_list(
+        let vars_offset = resource_error_call_result!(
-            &mut self.heap,
+            self,
-            var_list.into_iter().map(|(_, cell, _)| cell)
+            sized_iter_to_heap_list(
-        ));
+                &mut self.heap,
+                var_list.len(),
+                var_list.iter().map(|(_, cell, _)| *cell),
+            )
+        );
 
         unify_fn!(*self, vars_offset, vars_addr);
 
@@ -578,24 +644,27 @@ impl MachineState {
         }
 
         let var_names_addr = self.registers[5];
-        let var_names_offset = heap_loc_as_cell!(iter_to_heap_list(
+        let var_names_offset = resource_error_call_result!(
-            &mut self.heap,
+            self,
-            list_of_var_eqs.into_iter()
+            push_var_eq_functors(
-        ));
+                &mut self.heap,
-
+                var_list.len(),
-        Ok(unify_fn!(*self, var_names_offset, var_names_addr))
+                var_list.iter().filter_map(|(var_name, var, _)| {
+                    if var_name.is_anon() {
+                        None
+                    } else {
+                        Some((var_name, var))
+                    }
+                }),
+                &self.atom_tbl,
+            )
+        );
+        unify_fn!(*self, var_names_offset, var_names_addr);
+        Ok(())
     }
 
     pub fn read_term_body(&mut self, mut term_write_result: TermWriteResult) -> CallResult {
-        let heap_loc = read_heap_cell!(self.heap[term_write_result.heap_loc],
+        let heap_loc = heap_loc_as_cell!(term_write_result.heap_loc);
-            (HeapCellValueTag::PStr | HeapCellValueTag::PStrOffset) => {
-                pstr_loc_as_cell!(term_write_result.heap_loc)
-            }
-            _ => {
-                heap_loc_as_cell!(term_write_result.heap_loc)
-            }
-        );
-
         unify_fn!(*self, heap_loc, self.registers[2]);
 
         if self.fail {
@@ -607,10 +676,9 @@ impl MachineState {
         }
 
         let mut singleton_var_set: IndexMap<Ref, bool> = IndexMap::new();
+        self.heap[0] = heap_loc;
 
-        for cell in
+        for cell in stackful_preorder_iter::<NonListElider>(&mut self.heap, &mut self.stack, 0) {
-            stackful_preorder_iter::<NonListElider>(&mut self.heap, &mut self.stack, heap_loc)
-        {
             let cell = unmark_cell_bits!(cell);
 
             if let Some(var) = cell.as_var() {
@@ -622,29 +690,29 @@ impl MachineState {
             }
         }
 
-        let singleton_var_list = push_var_eq_functors(
+        let singleton_var_list = resource_error_call_result!(
-            &mut self.heap,
+            self,
-            term_write_result
+            push_var_eq_functors(
-                .var_dict
+                &mut self.heap,
-                .iter()
+                term_write_result.var_dict.len(),
-                .filter(|(var_name, binding)| {
+                term_write_result
-                    if var_name.is_anon() {
+                    .var_dict
-                        return false;
+                    .iter()
-                    }
+                    .filter(|(var_name, binding)| {
+                        if var_name.is_anon() {
+                            return false;
+                        }
 
-                    if let Some(r) = binding.as_var() {
+                        if let Some(r) = binding.as_var() {
-                        *singleton_var_set.get(&r).unwrap_or(&false)
+                            *singleton_var_set.get(&r).unwrap_or(&false)
-                    } else {
+                        } else {
-                        false
+                            false
-                    }
+                        }
-                }),
+                    }),
-            &self.atom_tbl,
+                &self.atom_tbl,
+            )
         );
 
-        for var in term_write_result.var_dict.values_mut() {
-            *var = heap_bound_deref(&self.heap, *var);
-        }
-
         let mut var_list = Vec::with_capacity(singleton_var_set.len());
 
         for (var_name, addr) in term_write_result.var_dict {
@@ -741,7 +809,8 @@ impl MachineState {
                         CompilationError::ParserError(e) if e.is_unexpected_eof() => {
                             match eof_handler(self, stream)? {
                                 OnEOF::Return => {
-                                    return self.write_read_term_options(vec![], vec![])
+                                    return self
+                                        .write_read_term_options(vec![], empty_list_as_cell!());
                                 }
                                 OnEOF::Continue => continue,
                             }
@@ -790,19 +859,16 @@ impl MachineState {
                                 }
 
                                 read_heap_cell!(atom,
-                                    (HeapCellValueTag::Char, c) => {
-                                        var_names.insert(var, VarPtr::from(c.to_string()));
-                                    }
                                     (HeapCellValueTag::Atom, (name, _arity)) => {
                                         debug_assert_eq!(_arity, 0);
-                                        var_names.insert(var, VarPtr::from(&*name.as_str()));
+                                        var_names.insert(var, VarPtr::from(name.as_str().to_owned()));
                                     }
                                     (HeapCellValueTag::Str, s) => {
                                         let (name, arity) = cell_as_atom_cell!(self.heap[s])
                                             .get_name_and_arity();
 
                                         debug_assert_eq!(arity, 0);
-                                        var_names.insert(var, VarPtr::from(&*name.as_str()));
+                                        var_names.insert(var, VarPtr::from(name.as_str().to_owned()));
                                     }
                                     _ => {
                                         unreachable!();
@@ -881,13 +947,15 @@ impl MachineState {
                     }
                 );
 
+                self.heap[0] = term_to_be_printed;
+
                 let mut printer = HCPrinter::new(
                     &mut self.heap,
-                    Arc::clone(&self.atom_tbl),
                     &mut self.stack,
+                    &self.arena,
                     op_dir,
                     PrinterOutputter::new(),
-                    term_to_be_printed,
+                    0,
                 );
 
                 printer.ignore_ops = ignore_ops;
@@ -895,7 +963,7 @@ impl MachineState {
                 printer.quoted = quoted;
                 printer.double_quotes = double_quotes;
 
-                match Number::try_from(max_depth) {
+                match Number::try_from((max_depth, &self.arena.f64_tbl)) {
                     Ok(Number::Fixnum(n)) => {
                         if let Ok(n) = usize::try_from(n.get_num()) {
                             printer.max_depth = n;
@@ -920,7 +988,6 @@ impl MachineState {
                 }
 
                 printer.var_names = var_names;
-
                 printer
             }
             Err(err) => {
@@ -937,7 +1004,10 @@ impl MachineState {
         arity: HeapCellValue,
     ) -> (Atom, usize) {
         let name = cell_as_atom!(self.store(self.deref(name)));
-        let arity = cell_as_fixnum!(self.store(self.deref(arity)));
+        let arity = unsafe {
+            self.store(self.deref(arity))
+                .to_fixnum_or_cut_point_unchecked()
+        };
 
         (name, usize::try_from(arity.get_num()).unwrap())
     }
@@ -978,42 +1048,6 @@ impl MachineState {
             }
         );
     }
-
-    pub(crate) fn directive_error(&mut self, err: DirectiveError) -> MachineError {
-        match err {
-            DirectiveError::ExpectedDirective(_term) => self.domain_error(
-                DomainErrorType::Directive,
-                atom_as_cell!(atom!("todo_insert_invalid_term_here")),
-            ),
-            DirectiveError::InvalidDirective(name, arity) => {
-                self.domain_error(DomainErrorType::Directive, functor_stub(name, arity))
-            }
-            DirectiveError::InvalidOpDeclNameType(_term) => self.type_error(
-                ValidType::List,
-                atom_as_cell!(atom!("todo_insert_invalid_term_here")),
-            ),
-            DirectiveError::InvalidOpDeclSpecDomain(_term) => self.domain_error(
-                DomainErrorType::OperatorSpecifier,
-                atom_as_cell!(atom!("todo_insert_invalid_term_here")),
-            ),
-            DirectiveError::InvalidOpDeclSpecValue(atom) => {
-                self.domain_error(DomainErrorType::OperatorSpecifier, atom_as_cell!(atom))
-            }
-            DirectiveError::InvalidOpDeclPrecType(_term) => self.type_error(
-                ValidType::Integer,
-                atom_as_cell!(atom!("todo_insert_invalid_term_here")),
-            ),
-            DirectiveError::InvalidOpDeclPrecDomain(num) => {
-                self.domain_error(DomainErrorType::OperatorPriority, fixnum_as_cell!(num))
-            }
-            DirectiveError::ShallNotCreate(atom) => {
-                self.permission_error(Permission::Create, atom!("operator"), atom)
-            }
-            DirectiveError::ShallNotModify(atom) => {
-                self.permission_error(Permission::Modify, atom!("operator"), atom)
-            }
-        }
-    }
 }
 
 #[allow(clippy::upper_case_acronyms)]

src/machine/mock_wam.rs

@@ -4,16 +4,13 @@ pub use crate::machine::machine_state::*;
 pub use crate::machine::streams::*;
 pub use crate::machine::*;
 pub use crate::parser::ast::*;
-use crate::read::*;
-pub use crate::types::*;
-
-use std::sync::Arc;
 
 #[cfg(test)]
 use crate::machine::copier::CopierTarget;
+use crate::read::TermWriteResult;
 
 #[cfg(test)]
-use std::ops::{Deref, DerefMut, Index, IndexMut};
+use std::ops::{Deref, DerefMut, Index, IndexMut, Range};
 
 // a mini-WAM for test purposes.
 
@@ -31,7 +28,6 @@ impl MockWAM {
         Self {
             machine_st: MachineState::new(),
             op_dir,
-            //flags: MachineFlags::default(),
         }
     }
 
@@ -55,16 +51,15 @@ impl MockWAM {
         term_string: &'static str,
     ) -> Result<String, CompilationError> {
         let term_write_result = self.parse_and_write_parsed_term_to_heap(term_string)?;
-
+        print_heap_terms(&self.machine_st.heap, term_write_result.heap_loc);
-        print_heap_terms(self.machine_st.heap.iter(), term_write_result.heap_loc);
 
         let mut printer = HCPrinter::new(
             &mut self.machine_st.heap,
-            Arc::clone(&self.machine_st.atom_tbl),
             &mut self.machine_st.stack,
+            &self.machine_st.arena,
             &self.op_dir,
             PrinterOutputter::new(),
-            heap_loc_as_cell!(term_write_result.heap_loc),
+            term_write_result.heap_loc,
         );
 
         printer.var_names = term_write_result
@@ -95,6 +90,7 @@ pub struct TermCopyingMockWAM<'a> {
 impl<'a> Index<usize> for TermCopyingMockWAM<'a> {
     type Output = HeapCellValue;
 
+    #[inline]
     fn index(&self, index: usize) -> &HeapCellValue {
         &self.wam.machine_st.heap[index]
     }
@@ -112,6 +108,7 @@ impl<'a> IndexMut<usize> for TermCopyingMockWAM<'a> {
 impl<'a> Deref for TermCopyingMockWAM<'a> {
     type Target = MockWAM;
 
+    #[inline]
     fn deref(&self) -> &Self::Target {
         self.wam
     }
@@ -119,6 +116,7 @@ impl<'a> Deref for TermCopyingMockWAM<'a> {
 
 #[cfg(test)]
 impl<'a> DerefMut for TermCopyingMockWAM<'a> {
+    #[inline]
     fn deref_mut(&mut self) -> &mut Self::Target {
         self.wam
     }
@@ -153,10 +151,6 @@ impl<'a> CopierTarget for TermCopyingMockWAM<'a> {
         }
     }
 
-    fn push(&mut self, val: HeapCellValue) {
-        self.wam.machine_st.heap.push(val);
-    }
-
     fn push_attr_var_queue(&mut self, attr_var_loc: usize) {
         self.wam
             .machine_st
@@ -170,43 +164,66 @@ impl<'a> CopierTarget for TermCopyingMockWAM<'a> {
     }
 
     fn threshold(&self) -> usize {
-        self.wam.machine_st.heap.len()
+        self.wam.machine_st.heap.cell_len()
+    }
+
+    #[inline(always)]
+    fn copy_pstr_to_threshold(&mut self, pstr_loc: usize) -> Result<usize, usize> {
+        self.wam.machine_st.heap.copy_pstr_within(pstr_loc)
+    }
+
+    #[inline(always)]
+    fn as_slice_from<'b>(&'b self, from: usize) -> Box<dyn Iterator<Item = u8> + 'b> {
+        Box::new(self.wam.machine_st.heap.as_slice()[from..].iter().cloned())
+    }
+
+    #[inline(always)]
+    fn reserve(&mut self, num_cells: usize) -> Result<HeapWriter, usize> {
+        self.wam.machine_st.heap.reserve(num_cells)
+    }
+
+    #[inline(always)]
+    fn copy_slice_to_end(&mut self, bounds: Range<usize>) -> Result<(), usize> {
+        self.wam.machine_st.heap.copy_slice_to_end(bounds)
     }
 }
 
 #[cfg(test)]
-pub fn all_cells_marked_and_unforwarded(heap: &[HeapCellValue]) {
+pub fn all_cells_marked_and_unforwarded(heap: &Heap, offset: usize) {
-    for (idx, cell) in heap.iter().enumerate() {
+    for curr_idx in offset..heap.cell_len() {
+        let cell = heap[curr_idx];
+
         assert!(
             cell.get_mark_bit(),
-            "cell {:?} at index {} is not marked",
+            "cell {cell:?} at index {curr_idx} is not marked"
-            cell,
-            idx
         );
         assert!(
             !cell.get_forwarding_bit(),
-            "cell {:?} at index {} is forwarded",
+            "cell {cell:?} at index {curr_idx} is forwarded"
-            cell,
-            idx
         );
     }
 }
 
 #[cfg(test)]
-pub fn all_cells_unmarked(heap: &Heap) {
+pub fn unmark_all_cells(heap: &mut Heap, offset: usize) {
-    for (idx, cell) in heap.iter().enumerate() {
+    for idx in offset..heap.cell_len() {
-        assert!(
+        heap[idx].set_mark_bit(false);
-            !cell.get_mark_bit(),
+    }
-            "cell {:?} at index {} is still marked",
+}
-            cell,
+
-            idx
+#[cfg(test)]
-        );
+pub fn all_cells_unmarked(iter: &impl SizedHeap) {
+    let mut idx = 0;
+    let cell_len = iter.cell_len();
+
+    while idx < cell_len {
+        let curr_idx = idx;
+        idx += 1;
+        let cell = iter[curr_idx];
 
         assert!(
-            !cell.get_forwarding_bit(),
+            !cell.get_mark_bit(),
-            "cell {:?} at index {} is still forwarded",
+            "cell {cell:?} at index {curr_idx} is still marked"
-            cell,
-            idx
         );
     }
 }
@@ -232,6 +249,7 @@ pub(crate) fn parse_and_write_parsed_term_to_heap(
 
 impl Machine {
     /// For use in tests.
+    #[allow(clippy::unbuffered_bytes)]
     pub fn test_load_file(&mut self, file: &str) -> Vec<u8> {
         let stream = Stream::from_owned_string(
             std::fs::read_to_string(AsRef::<std::path::Path>::as_ref(file)).unwrap(),
@@ -243,6 +261,7 @@ impl Machine {
     }
 
     /// For use in tests.
+    #[allow(clippy::unbuffered_bytes)]
     pub fn test_load_string(&mut self, code: &str) -> Vec<u8> {
         let stream = Stream::from_owned_string(code.to_owned(), &mut self.machine_st.arena);
 
@@ -255,6 +274,8 @@ impl Machine {
 mod tests {
     use super::*;
 
+    use crate::functor_macro::FunctorElement;
+
     #[test]
     fn unify_tests() {
         let mut wam = MachineState::new();
@@ -387,36 +408,66 @@ mod tests {
 
         wam.heap.clear();
 
-        wam.heap.push(pstr_as_cell!(atom!("this is a string")));
+        let mut writer = wam.heap.reserve(96).unwrap();
-        wam.heap.push(heap_loc_as_cell!(1));
 
-        wam.heap.push(pstr_as_cell!(atom!("this is a string")));
+        writer.write_with(|section| {
-        wam.heap.push(pstr_loc_as_cell!(4));
+            section.push_pstr("this is a string"); // 0
 
-        wam.heap.push(pstr_offset_as_cell!(0));
+            let h = section.cell_len();
-        wam.heap.push(fixnum_as_cell!(Fixnum::build_with(6)));
+            assert_eq!(h, 3);
 
-        unify!(wam, pstr_loc_as_cell!(0), pstr_loc_as_cell!(2));
+            section.push_cell(heap_loc_as_cell!(h)); // 3
+            section.push_pstr("this is a string"); // 4
+
+            let h = section.cell_len();
+            assert_eq!(h + 1, 8);
+
+            section.push_cell(pstr_loc_as_cell!(heap_index!(h + 1))); // 7
+            section.push_pstr("this is a string"); // 8
+
+            section.push_cell(pstr_loc_as_cell!(heap_index!(h + 1)));
+        });
+
+        unify!(wam, pstr_loc_as_cell!(0), pstr_loc_as_cell!(heap_index!(4)));
 
         assert!(!wam.fail);
 
-        assert_eq!(wam.heap[1], pstr_loc_as_cell!(4));
+        assert_eq!(
-
+            wam.heap
-        all_cells_unmarked(&wam.heap);
+                .slice_to_str(heap_index!(0), "this is a string".len()),
+            "this is a string"
+        );
+        assert_eq!(wam.heap[3], pstr_loc_as_cell!(heap_index!(8)));
+        assert_eq!(
+            wam.heap
+                .slice_to_str(heap_index!(4), "this is a string".len()),
+            "this is a string"
+        );
+        assert_eq!(wam.heap[7], pstr_loc_as_cell!(heap_index!(8)));
+        assert_eq!(
+            wam.heap
+                .slice_to_str(heap_index!(8), "this is a string".len()),
+            "this is a string"
+        );
+        assert_eq!(wam.heap[11], pstr_loc_as_cell!(heap_index!(8)));
 
         wam.heap.clear();
 
-        wam.heap.push(list_loc_as_cell!(1));
+        let mut writer = wam.heap.reserve(96).unwrap();
-        wam.heap.push(atom_as_cell!(atom!("a")));
-        wam.heap.push(list_loc_as_cell!(3));
-        wam.heap.push(atom_as_cell!(atom!("b")));
-        wam.heap.push(heap_loc_as_cell!(0));
 
-        wam.heap.push(list_loc_as_cell!(6));
+        writer.write_with(|section| {
-        wam.heap.push(atom_as_cell!(atom!("a")));
+            section.push_cell(list_loc_as_cell!(1));
-        wam.heap.push(list_loc_as_cell!(8));
+            section.push_cell(atom_as_cell!(atom!("a")));
-        wam.heap.push(atom_as_cell!(atom!("b")));
+            section.push_cell(list_loc_as_cell!(3));
-        wam.heap.push(heap_loc_as_cell!(5));
+            section.push_cell(atom_as_cell!(atom!("b")));
+            section.push_cell(heap_loc_as_cell!(0));
+
+            section.push_cell(list_loc_as_cell!(6));
+            section.push_cell(atom_as_cell!(atom!("a")));
+            section.push_cell(list_loc_as_cell!(8));
+            section.push_cell(atom_as_cell!(atom!("b")));
+            section.push_cell(heap_loc_as_cell!(5));
+        });
 
         unify!(wam, heap_loc_as_cell!(0), heap_loc_as_cell!(5));
 
@@ -426,17 +477,21 @@ mod tests {
 
         wam.heap.clear();
 
-        wam.heap.push(list_loc_as_cell!(1));
+        let mut writer = wam.heap.reserve(96).unwrap();
-        wam.heap.push(atom_as_cell!(atom!("a")));
-        wam.heap.push(list_loc_as_cell!(3));
-        wam.heap.push(atom_as_cell!(atom!("b")));
-        wam.heap.push(heap_loc_as_cell!(0));
 
-        wam.heap.push(list_loc_as_cell!(6));
+        writer.write_with(|section| {
-        wam.heap.push(atom_as_cell!(atom!("a")));
+            section.push_cell(list_loc_as_cell!(1));
-        wam.heap.push(list_loc_as_cell!(8));
+            section.push_cell(atom_as_cell!(atom!("a")));
-        wam.heap.push(atom_as_cell!(atom!("c")));
+            section.push_cell(list_loc_as_cell!(3));
-        wam.heap.push(heap_loc_as_cell!(5));
+            section.push_cell(atom_as_cell!(atom!("b")));
+            section.push_cell(heap_loc_as_cell!(0));
+
+            section.push_cell(list_loc_as_cell!(6));
+            section.push_cell(atom_as_cell!(atom!("a")));
+            section.push_cell(list_loc_as_cell!(8));
+            section.push_cell(atom_as_cell!(atom!("c")));
+            section.push_cell(heap_loc_as_cell!(5));
+        });
 
         unify!(wam, heap_loc_as_cell!(0), heap_loc_as_cell!(5));
 
@@ -444,19 +499,24 @@ mod tests {
 
         wam.fail = false;
         all_cells_unmarked(&wam.heap);
+
         wam.heap.clear();
 
-        wam.heap.push(list_loc_as_cell!(1));
+        let mut writer = wam.heap.reserve(96).unwrap();
-        wam.heap.push(atom_as_cell!(atom!("a")));
-        wam.heap.push(list_loc_as_cell!(3));
-        wam.heap.push(atom_as_cell!(atom!("b")));
-        wam.heap.push(heap_loc_as_cell!(5));
 
-        wam.heap.push(list_loc_as_cell!(6));
+        writer.write_with(|section| {
-        wam.heap.push(atom_as_cell!(atom!("a")));
+            section.push_cell(list_loc_as_cell!(1));
-        wam.heap.push(list_loc_as_cell!(8));
+            section.push_cell(atom_as_cell!(atom!("a")));
-        wam.heap.push(atom_as_cell!(atom!("b")));
+            section.push_cell(list_loc_as_cell!(3));
-        wam.heap.push(heap_loc_as_cell!(0));
+            section.push_cell(atom_as_cell!(atom!("b")));
+            section.push_cell(heap_loc_as_cell!(5));
+
+            section.push_cell(list_loc_as_cell!(6));
+            section.push_cell(atom_as_cell!(atom!("a")));
+            section.push_cell(list_loc_as_cell!(8));
+            section.push_cell(atom_as_cell!(atom!("b")));
+            section.push_cell(heap_loc_as_cell!(0));
+        });
 
         unify!(wam, heap_loc_as_cell!(0), heap_loc_as_cell!(5));
 
@@ -468,7 +528,7 @@ mod tests {
             let term_write_result_1 =
                 parse_and_write_parsed_term_to_heap(&mut wam, "X = g(X,y).", &op_dir).unwrap();
 
-            print_heap_terms(wam.heap.iter(), term_write_result_1.heap_loc);
+            print_heap_terms(&wam.heap, term_write_result_1.heap_loc);
 
             unify!(wam, heap_loc_as_cell!(2), str_loc_as_cell!(4));
 
@@ -510,8 +570,15 @@ mod tests {
 
         let mut wam = MachineState::new();
 
-        wam.heap.push(heap_loc_as_cell!(0));
+        // clear the heap of resource error data etc
-        wam.heap.push(heap_loc_as_cell!(1));
+        wam.heap.clear();
+
+        let mut writer = wam.heap.reserve(96).unwrap();
+
+        writer.write_with(|section| {
+            section.push_cell(heap_loc_as_cell!(0));
+            section.push_cell(heap_loc_as_cell!(1));
+        });
 
         assert_eq!(
             compare_term_test!(wam, wam.heap[0], wam.heap[1]),
@@ -533,12 +600,10 @@ mod tests {
             Some(Ordering::Equal)
         );
 
+        let cstr_cell = wam.heap.allocate_cstr("string").unwrap();
+
         assert_eq!(
-            compare_term_test!(
+            compare_term_test!(wam, atom_as_cell!(atom!("atom")), cstr_cell),
-                wam,
-                atom_as_cell!(atom!("atom")),
-                atom_as_cstr_cell!(atom!("string"))
-            ),
             Some(Ordering::Less)
         );
 
@@ -571,8 +636,12 @@ mod tests {
 
         wam.heap.clear();
 
-        wam.heap.push(atom_as_cell!(atom!("f"), 1));
+        let mut writer = wam.heap.reserve(96).unwrap();
-        wam.heap.push(heap_loc_as_cell!(1));
+
+        writer.write_with(|section| {
+            section.push_cell(atom_as_cell!(atom!("f"), 1));
+            section.push_cell(heap_loc_as_cell!(1));
+        });
 
         assert_eq!(
             compare_term_test!(wam, heap_loc_as_cell!(0), heap_loc_as_cell!(0)),
@@ -586,21 +655,25 @@ mod tests {
 
         wam.heap.clear();
 
-        // [1,2,3]
+        let mut writer = wam.heap.reserve(96).unwrap();
-        wam.heap.push(list_loc_as_cell!(1));
-        wam.heap.push(fixnum_as_cell!(Fixnum::build_with(1)));
-        wam.heap.push(list_loc_as_cell!(3));
-        wam.heap.push(fixnum_as_cell!(Fixnum::build_with(2)));
-        wam.heap.push(list_loc_as_cell!(5));
-        wam.heap.push(fixnum_as_cell!(Fixnum::build_with(3)));
-        wam.heap.push(empty_list_as_cell!());
 
-        // [1,2]
+        writer.write_with(|section| {
-        wam.heap.push(list_loc_as_cell!(8));
+            // [1,2,3]
-        wam.heap.push(fixnum_as_cell!(Fixnum::build_with(1)));
+            section.push_cell(list_loc_as_cell!(1));
-        wam.heap.push(list_loc_as_cell!(10));
+            section.push_cell(fixnum_as_cell!(Fixnum::build_with(1)));
-        wam.heap.push(fixnum_as_cell!(Fixnum::build_with(2)));
+            section.push_cell(list_loc_as_cell!(3));
-        wam.heap.push(empty_list_as_cell!());
+            section.push_cell(fixnum_as_cell!(Fixnum::build_with(2)));
+            section.push_cell(list_loc_as_cell!(5));
+            section.push_cell(fixnum_as_cell!(Fixnum::build_with(3)));
+            section.push_cell(empty_list_as_cell!());
+
+            // [1,2]
+            section.push_cell(list_loc_as_cell!(8));
+            section.push_cell(fixnum_as_cell!(Fixnum::build_with(1)));
+            section.push_cell(list_loc_as_cell!(10));
+            section.push_cell(fixnum_as_cell!(Fixnum::build_with(2)));
+            section.push_cell(empty_list_as_cell!());
+        });
 
         assert_eq!(
             compare_term_test!(wam, heap_loc_as_cell!(7), heap_loc_as_cell!(7)),
@@ -626,12 +699,10 @@ mod tests {
             Some(Ordering::Greater)
         );
 
+        let cstr_cell = wam.heap.allocate_cstr("string").unwrap();
+
         assert_eq!(
-            compare_term_test!(
+            compare_term_test!(wam, empty_list_as_cell!(), cstr_cell),
-                wam,
-                empty_list_as_cell!(),
-                atom_as_cstr_cell!(atom!("string"))
-            ),
             Some(Ordering::Less)
         );
 
@@ -662,55 +733,63 @@ mod tests {
     fn is_cyclic_term_tests() {
         let mut wam = MachineState::new();
 
-        assert!(!wam.is_cyclic_term(atom_as_cell!(atom!("f"))));
+        let mut writer = wam.heap.reserve(96).unwrap();
-        assert!(!wam.is_cyclic_term(fixnum_as_cell!(Fixnum::build_with(555))));
 
-        wam.heap.push(heap_loc_as_cell!(0));
+        writer.write_with(|section| {
+            section.push_cell(atom_as_cell!(atom!("f")));
+            section.push_cell(fixnum_as_cell!(Fixnum::build_with(555)));
+            section.push_cell(heap_loc_as_cell!(0));
+        });
 
-        assert!(!wam.is_cyclic_term(heap_loc_as_cell!(0)));
+        assert!(!wam.is_cyclic_term(0));
+        assert!(!wam.is_cyclic_term(1));
+        assert!(!wam.is_cyclic_term(2));
 
         all_cells_unmarked(&wam.heap);
         wam.heap.clear();
 
-        wam.heap
+        let mut functor_writer = Heap::functor_writer(functor!(
-            .extend(functor!(atom!("f"), [atom(atom!("a")), atom(atom!("b"))]));
+            atom!("f"),
+            [atom_as_cell((atom!("a"))), atom_as_cell((atom!("b")))]
+        ));
 
-        assert!(!wam.is_cyclic_term(str_loc_as_cell!(0)));
+        functor_writer(&mut wam.heap).unwrap();
+
+        let h = wam.heap.cell_len();
+        wam.heap.push_cell(str_loc_as_cell!(0)).unwrap();
+
+        assert!(!wam.is_cyclic_term(h));
 
         all_cells_unmarked(&wam.heap);
 
-        assert!(!wam.is_cyclic_term(heap_loc_as_cell!(1)));
+        assert!(!wam.is_cyclic_term(1));
 
         all_cells_unmarked(&wam.heap);
 
-        assert!(!wam.is_cyclic_term(heap_loc_as_cell!(2)));
+        assert!(!wam.is_cyclic_term(2));
 
         all_cells_unmarked(&wam.heap);
 
         wam.heap[2] = str_loc_as_cell!(0);
 
-        print_heap_terms(wam.heap.iter(), 0);
+        print_heap_terms(&wam.heap, 0);
 
-        assert!(wam.is_cyclic_term(str_loc_as_cell!(0)));
+        assert!(wam.is_cyclic_term(2));
 
         all_cells_unmarked(&wam.heap);
 
         wam.heap[2] = atom_as_cell!(atom!("b"));
         wam.heap[1] = str_loc_as_cell!(0);
 
-        assert!(wam.is_cyclic_term(str_loc_as_cell!(0)));
+        assert!(wam.is_cyclic_term(1));
-
-        all_cells_unmarked(&wam.heap);
-
-        assert!(wam.is_cyclic_term(heap_loc_as_cell!(1)));
 
         all_cells_unmarked(&wam.heap);
 
         wam.heap.clear();
 
-        wam.heap.push(pstr_as_cell!(atom!("a string")));
+        let h = wam.heap.cell_len();
-        wam.heap.push(empty_list_as_cell!());
+        wam.heap.allocate_cstr("a string").unwrap();
 
-        assert!(!wam.is_cyclic_term(pstr_loc_as_cell!(0)));
+        assert!(!wam.is_cyclic_term(h));
     }
 }

src/machine/mod.rs

@@ -45,6 +45,7 @@ use crate::machine::machine_indices::*;
 use crate::machine::machine_state::*;
 use crate::machine::stack::*;
 use crate::machine::streams::*;
+use crate::offset_table::*;
 use crate::parser::ast::*;
 use crate::parser::dashu::{Integer, Rational};
 use crate::types::*;
@@ -207,13 +208,8 @@ pub(crate) fn import_builtin_impls(code_dir: &CodeDir, builtins: &mut Module) {
 #[inline]
 pub(crate) fn get_structure_index(value: HeapCellValue) -> Option<CodeIndex> {
     read_heap_cell!(value,
-        (HeapCellValueTag::Cons, cons_ptr) => {
+        (HeapCellValueTag::CodeIndexOffset, offset) => {
-             match_untyped_arena_ptr!(cons_ptr,
+            return Some(CodeIndex::from(offset));
-                 (ArenaHeaderTag::IndexPtr, ip) => {
-                     return Some(CodeIndex::from(ip));
-                 }
-                 _ => {}
-             );
         }
         _ => {
         }
@@ -246,7 +242,7 @@ impl Machine {
     }
 
     /// Runs the predicate `key` in `module_name` until completion.
-    /// Siltently ignores failure, thrown errors and choice points.
+    /// Silently ignores failure, thrown errors and choice points.
     ///
     /// Consider using [`Machine::run_query`] if you wish to handle
     /// predicates that may fail, leave a choice point or throw.
@@ -256,8 +252,14 @@ impl Machine {
         key: PredicateKey,
     ) -> std::process::ExitCode {
         if let Some(module) = self.indices.modules.get(&module_name) {
-            if let Some(code_index) = module.code_dir.get(&key) {
+            if let Some(code_idx) = module.code_dir.get(&key) {
-                let p = code_index.local().unwrap();
+                let index_ptr = self
+                    .machine_st
+                    .arena
+                    .code_index_tbl
+                    .get_entry(code_idx.into());
+                let p = index_ptr.local().unwrap();
+
                 // Leave a halting choice point to backtrack to in case the predicate fails or throws.
                 self.allocate_stub_choice_point();
 
@@ -328,8 +330,13 @@ impl Machine {
         self.load_file(path_buf.to_str().unwrap(), stream);
 
         if let Some(module) = self.indices.modules.get(&atom!("$atts")) {
-            if let Some(code_index) = module.code_dir.get(&(atom!("driver"), 2)) {
+            if let Some(code_idx) = module.code_dir.get(&(atom!("driver"), 2)) {
-                self.machine_st.attr_var_init.verify_attrs_loc = code_index.local().unwrap();
+                let index_ptr = self
+                    .machine_st
+                    .arena
+                    .code_index_tbl
+                    .get_entry(code_idx.into());
+                self.machine_st.attr_var_init.verify_attrs_loc = index_ptr.local().unwrap();
             }
         }
     }
@@ -343,13 +350,16 @@ impl Machine {
             for arity in 1..66 {
                 let key = (atom!("call"), arity);
 
-                match loader.code_dir.get(&key) {
+                match loader.code_dir.get(&key).cloned() {
                     Some(src_code_index) => {
-                        let target_code_index = target_code_dir
+                        let code_index_tbl = &mut arena.code_index_tbl;
-                            .entry(key)
-                            .or_insert_with(|| CodeIndex::new(IndexPtr::undefined(), arena));
 
-                        target_code_index.set(src_code_index.get());
+                        let target_code_index = target_code_dir.entry(key).or_insert_with(|| {
+                            CodeIndex::new(IndexPtr::undefined(), code_index_tbl)
+                        });
+
+                        let src_code_ptr = code_index_tbl.get_entry(src_code_index.into());
+                        target_code_index.set(code_index_tbl, src_code_ptr);
                     }
                     None => {
                         unreachable!();
@@ -458,7 +468,7 @@ impl Machine {
                 key,
                 CodeIndex::new(
                     IndexPtr::index(p + impls_offset),
-                    &mut self.machine_st.arena,
+                    &mut self.machine_st.arena.code_index_tbl,
                 ),
             );
         }
@@ -485,7 +495,10 @@ impl Machine {
     #[inline(always)]
     pub(crate) fn run_verify_attr_interrupt(&mut self, arity: usize) {
         let p = self.machine_st.attr_var_init.verify_attrs_loc;
-        self.machine_st.verify_attr_interrupt(p, arity);
+        step_or_resource_error!(
+            self.machine_st,
+            self.machine_st.verify_attr_interrupt(p, arity)
+        );
     }
 
     fn next_clause_applicable(&mut self, mut offset: usize) -> bool {
@@ -509,8 +522,8 @@ impl Machine {
                                     .select_switch_on_term_index(cell, v, c, l, s)
                             }
                             IndexingLine::Indexing(IndexingInstruction::SwitchOnConstant(hm)) => {
-                                let lit = self.machine_st.constant_to_literal(cell);
+                                // let lit = self.machine_st.constant_to_literal(cell);
-                                hm.get(&lit).cloned().unwrap_or(IndexingCodePtr::Fail)
+                                hm.get(&cell).cloned().unwrap_or(IndexingCodePtr::Fail)
                             }
                             IndexingLine::Indexing(IndexingInstruction::SwitchOnStructure(hm)) => {
                                 self.machine_st.select_switch_on_structure_index(cell, hm)
@@ -536,34 +549,8 @@ impl Machine {
 
                     if cell.is_var() {
                         offset += 1;
-                    } else if lit.get_tag() == HeapCellValueTag::CStr {
-                        read_heap_cell!(cell,
-                            (HeapCellValueTag::CStr) => {
-                                if cell == lit {
-                                    offset += 1;
-                                } else {
-                                    return false;
-                                }
-                            }
-                            (HeapCellValueTag::Lis | HeapCellValueTag::PStrLoc) => {
-                                offset += 1;
-                            }
-                            (HeapCellValueTag::Str, s) => {
-                                let (name, arity) = cell_as_atom_cell!(self.machine_st.heap[s])
-                                    .get_name_and_arity();
-
-                                if name == atom!(".") && arity == 2 {
-                                    offset += 1;
-                                } else {
-                                    return false;
-                                }
-                            }
-                            _ => {
-                                return false;
-                            }
-                        );
                     } else {
-                        self.machine_st.write_literal_to_var(cell, lit);
+                        unify!(self.machine_st, cell, lit);
 
                         if self.machine_st.fail {
                             self.machine_st.fail = false;
@@ -577,7 +564,7 @@ impl Machine {
                     let cell = self.deref_register(t);
 
                     read_heap_cell!(cell,
-                        (HeapCellValueTag::Lis | HeapCellValueTag::PStrLoc | HeapCellValueTag::CStr) => {
+                        (HeapCellValueTag::Lis | HeapCellValueTag::PStrLoc) => {// | HeapCellValueTag::CStr) => {
                             offset += 1;
                         }
                         (HeapCellValueTag::Str, s) => {
@@ -616,27 +603,24 @@ impl Machine {
                         }
                     );
                 }
-                &Instruction::GetPartialString(
+                &Instruction::GetPartialString(Level::Shallow, ref string, RegType::Temp(t)) => {
-                    Level::Shallow,
-                    string,
-                    RegType::Temp(t),
-                    has_tail,
-                ) => {
                     let cell = self.deref_register(t);
 
                     read_heap_cell!(cell,
-                        (HeapCellValueTag::CStr, cstr) => {
+                        (HeapCellValueTag::PStrLoc, pstr_loc) => {
-                            if !has_tail && string != cstr {
+                            let heap_slice = &self.machine_st.heap.as_slice()[pstr_loc ..];
-                                return false;
-                            }
 
-                            offset += 1;
+                            match compare_pstr_slices(heap_slice, string.as_bytes()) {
+                                PStrSegmentCmpResult::Continue(..) => offset += 1,
+                                _ => return false,
+                            }
                         }
-                        (HeapCellValueTag::Lis | HeapCellValueTag::PStrLoc) => {
+                        (HeapCellValueTag::Lis) => {
                             offset += 1;
                         }
                         (HeapCellValueTag::Str, s) => {
-                            let (name, arity) = cell_as_atom_cell!(self.machine_st.heap[s]).get_name_and_arity();
+                            let (name, arity) = cell_as_atom_cell!(self.machine_st.heap[s])
+                                .get_name_and_arity();
 
                             if name == atom!(".") && arity == 2 {
                                 offset += 1;
@@ -759,7 +743,7 @@ impl Machine {
             or_frame.prelude.boip = 0;
             or_frame.prelude.biip = 0;
             or_frame.prelude.tr = self.machine_st.tr;
-            or_frame.prelude.h = self.machine_st.heap.len();
+            or_frame.prelude.h = self.machine_st.heap.cell_len();
             or_frame.prelude.b0 = self.machine_st.b0;
             or_frame.prelude.attr_var_queue_len =
                 self.machine_st.attr_var_init.attr_var_queue.len();
@@ -770,7 +754,7 @@ impl Machine {
                 or_frame[i] = self.machine_st.registers[i + 1];
             }
 
-            self.machine_st.hb = self.machine_st.heap.len();
+            self.machine_st.hb = self.machine_st.heap.cell_len();
         }
 
         self.machine_st.p += 1;
@@ -791,7 +775,7 @@ impl Machine {
             or_frame.prelude.boip = self.machine_st.oip;
             or_frame.prelude.biip = self.machine_st.iip + iip_offset; // 1
             or_frame.prelude.tr = self.machine_st.tr;
-            or_frame.prelude.h = self.machine_st.heap.len();
+            or_frame.prelude.h = self.machine_st.heap.cell_len();
             or_frame.prelude.b0 = self.machine_st.b0;
             or_frame.prelude.attr_var_queue_len =
                 self.machine_st.attr_var_init.attr_var_queue.len();
@@ -802,7 +786,7 @@ impl Machine {
                 or_frame[i] = self.machine_st.registers[i + 1];
             }
 
-            self.machine_st.hb = self.machine_st.heap.len();
+            self.machine_st.hb = self.machine_st.heap.cell_len();
 
             // self.machine_st.oip = 0;
             // self.machine_st.iip = 0;
@@ -1069,13 +1053,15 @@ impl Machine {
 
         if module_name == atom!("user") {
             if let Some(idx) = self.indices.code_dir.get(&(name, arity)).cloned() {
-                self.try_call(name, arity, idx.get())
+                let index_ptr = self.machine_st.arena.code_index_tbl.get_entry(idx.into());
+                self.try_call(name, arity, index_ptr)
             } else {
                 Err(self.machine_st.throw_undefined_error(name, arity))
             }
         } else if let Some(module) = self.indices.modules.get(&module_name) {
             if let Some(idx) = module.code_dir.get(&(name, arity)).cloned() {
-                self.try_call(name, arity, idx.get())
+                let index_ptr = self.machine_st.arena.code_index_tbl.get_entry(idx.into());
+                self.try_call(name, arity, index_ptr)
             } else {
                 self.undefined_procedure(name, arity)
             }
@@ -1098,14 +1084,24 @@ impl Machine {
         let (name, arity) = key;
 
         if module_name == atom!("user") {
-            if let Some(idx) = self.indices.code_dir.get(&(name, arity)).cloned() {
+            if let Some(offset) = self.indices.code_dir.get(&(name, arity)).cloned() {
-                self.try_execute(name, arity, idx.get())
+                let index_ptr = self
+                    .machine_st
+                    .arena
+                    .code_index_tbl
+                    .get_entry(offset.into());
+                self.try_execute(name, arity, index_ptr)
             } else {
                 self.undefined_procedure(name, arity)
             }
         } else if let Some(module) = self.indices.modules.get(&module_name) {
-            if let Some(idx) = module.code_dir.get(&(name, arity)).cloned() {
+            if let Some(offset) = module.code_dir.get(&(name, arity)).cloned() {
-                self.try_execute(name, arity, idx.get())
+                let index_ptr = self
+                    .machine_st
+                    .arena
+                    .code_index_tbl
+                    .get_entry(offset.into());
+                self.try_execute(name, arity, index_ptr)
             } else {
                 self.undefined_procedure(name, arity)
             }
@@ -1147,12 +1143,24 @@ impl Machine {
             let r_c_w_h = self
                 .indices
                 .get_predicate_code_index(r_c_w_h_atom, 0, iso_ext)
-                .and_then(|item| item.local())
+                .and_then(|code_idx| {
+                    self.machine_st
+                        .arena
+                        .code_index_tbl
+                        .get_entry(code_idx.into())
+                        .local()
+                })
                 .unwrap();
             let r_c_wo_h = self
                 .indices
                 .get_predicate_code_index(r_c_wo_h_atom, 1, iso_ext)
-                .and_then(|item| item.local())
+                .and_then(|code_idx| {
+                    self.machine_st
+                        .arena
+                        .code_index_tbl
+                        .get_entry(code_idx.into())
+                        .local()
+                })
                 .unwrap();
             (r_c_w_h, r_c_wo_h)
         });
@@ -1162,8 +1170,10 @@ impl Machine {
                 let (idx, arity) = if self.machine_st.effective_block() > prev_block {
                     (r_c_w_h, 0)
                 } else {
-                    self.machine_st.registers[1] =
+                    self.machine_st.registers[1] = fixnum_as_cell!(
-                        fixnum_as_cell!(Fixnum::build_with(b_cutoff as i64));
+                        /* FIXME this is not safe */
+                        unsafe { Fixnum::build_with_unchecked(b_cutoff as i64) }
+                    );
 
                     (r_c_wo_h, 1)
                 };

src/machine/preprocessor.rs

@@ -21,11 +21,10 @@ pub(crate) fn to_op_decl_spec(spec: Atom) -> Result<OpDeclSpec, CompilationError
     })
 }
 
-fn setup_op_decl(mut terms: Vec<Term>, atom_tbl: &AtomTable) -> Result<OpDecl, CompilationError> {
+fn setup_op_decl(mut terms: Vec<Term>) -> Result<OpDecl, CompilationError> {
     // should allow non-partial lists?
     let name = match terms.pop().unwrap() {
         Term::Literal(_, Literal::Atom(name)) => name,
-        Term::Literal(_, Literal::Char(c)) => AtomTable::build_with(atom_tbl, &c.to_string()),
         other => {
             return Err(CompilationError::InvalidDirective(
                 DirectiveError::InvalidOpDeclNameType(other),
@@ -112,16 +111,13 @@ fn setup_predicate_indicator(term: &mut Term) -> Result<PredicateKey, Compilatio
     }
 }
 
-fn setup_module_export(
+fn setup_module_export(mut term: Term) -> Result<ModuleExport, CompilationError> {
-    mut term: Term,
-    atom_tbl: &AtomTable,
-) -> Result<ModuleExport, CompilationError> {
     setup_predicate_indicator(&mut term)
         .map(ModuleExport::PredicateKey)
         .or_else(|_| {
             if let Term::Clause(_, name, terms) = term {
                 if terms.len() == 3 && name == atom!("op") {
-                    Ok(ModuleExport::OpDecl(setup_op_decl(terms, atom_tbl)?))
+                    Ok(ModuleExport::OpDecl(setup_op_decl(terms)?))
                 } else {
                     Err(CompilationError::InvalidModuleDecl)
                 }
@@ -140,12 +136,11 @@ pub(crate) fn build_rule_body(vars: &[Term], body_term: Term) -> Term {
 
 pub(super) fn setup_module_export_list(
     mut export_list: Term,
-    atom_tbl: &AtomTable,
 ) -> Result<Vec<ModuleExport>, CompilationError> {
     let mut exports = vec![];
 
     while let Term::Cons(_, t1, t2) = export_list {
-        let module_export = setup_module_export(*t1, atom_tbl)?;
+        let module_export = setup_module_export(*t1)?;
 
         exports.push(module_export);
         export_list = *t2;
@@ -158,10 +153,7 @@ pub(super) fn setup_module_export_list(
     }
 }
 
-fn setup_module_decl(
+fn setup_module_decl(mut terms: Vec<Term>) -> Result<ModuleDecl, CompilationError> {
-    mut terms: Vec<Term>,
-    atom_tbl: &AtomTable,
-) -> Result<ModuleDecl, CompilationError> {
     let export_list = terms.pop().unwrap();
     let name = terms.pop().unwrap();
 
@@ -171,8 +163,7 @@ fn setup_module_decl(
     }
     .ok_or(CompilationError::InvalidModuleDecl)?;
 
-    let exports = setup_module_export_list(export_list, atom_tbl)?;
+    let exports = setup_module_export_list(export_list)?;
-
     Ok(ModuleDecl { name, exports })
 }
 
@@ -191,10 +182,7 @@ fn setup_use_module_decl(mut terms: Vec<Term>) -> Result<ModuleSource, Compilati
 
 type UseModuleExport = (ModuleSource, IndexSet<ModuleExport>);
 
-fn setup_qualified_import(
+fn setup_qualified_import(mut terms: Vec<Term>) -> Result<UseModuleExport, CompilationError> {
-    mut terms: Vec<Term>,
-    atom_tbl: &AtomTable,
-) -> Result<UseModuleExport, CompilationError> {
     let mut export_list = terms.pop().unwrap();
     let module_src = match terms.pop().unwrap() {
         Term::Clause(_, name, mut terms) if name == atom!("library") && terms.len() == 1 => {
@@ -210,7 +198,7 @@ fn setup_qualified_import(
     let mut exports = IndexSet::new();
 
     while let Term::Cons(_, t1, t2) = export_list {
-        exports.insert(setup_module_export(*t1, atom_tbl)?);
+        exports.insert(setup_module_export(*t1)?);
         export_list = *t2;
     }
 
@@ -252,7 +240,7 @@ fn setup_qualified_import(
  * contained in src/lib/ops_and_meta_predicates.pl, which is loaded before
  * src/lib/builtins.pl.
  *
- * Meta-specs have three forms:
+ * Meta-specs have four forms:
  *
  * (:)  (the argument should be expanded with (:)/2 as described above)
  * +    (mode declarations under the mode syntax, which currently have no effect)
@@ -340,23 +328,15 @@ pub(super) fn setup_declaration<'a, LS: LoadState<'a>>(
                 let (name, arity) = setup_predicate_indicator(&mut terms.pop().unwrap())?;
                 Ok(Declaration::Dynamic(name, arity))
             }
-            (atom!("module"), 2) => {
+            (atom!("module"), 2) => Ok(Declaration::Module(setup_module_decl(terms)?)),
-                let atom_tbl = &mut LS::machine_st(&mut loader.payload).atom_tbl;
+            (atom!("op"), 3) => Ok(Declaration::Op(setup_op_decl(terms)?)),
-                Ok(Declaration::Module(setup_module_decl(terms, atom_tbl)?))
-            }
-            (atom!("op"), 3) => {
-                let atom_tbl = &mut LS::machine_st(&mut loader.payload).atom_tbl;
-                Ok(Declaration::Op(setup_op_decl(terms, atom_tbl)?))
-            }
             (atom!("non_counted_backtracking"), 1) => {
                 let (name, arity) = setup_predicate_indicator(&mut terms.pop().unwrap())?;
                 Ok(Declaration::NonCountedBacktracking(name, arity))
             }
             (atom!("use_module"), 1) => Ok(Declaration::UseModule(setup_use_module_decl(terms)?)),
             (atom!("use_module"), 2) => {
-                let atom_tbl = &mut LS::machine_st(&mut loader.payload).atom_tbl;
+                let (name, exports) = setup_qualified_import(terms)?;
-                let (name, exports) = setup_qualified_import(terms, atom_tbl)?;
-
                 Ok(Declaration::UseQualifiedModule(name, exports))
             }
             (atom!("meta_predicate"), 1) => {
@@ -444,7 +424,7 @@ fn build_meta_predicate_clause<'a, LS: LoadState<'a>>(
 
                 let term = match term {
                     Term::Clause(cell, name, mut terms) => {
-                        if let Some(Term::Literal(_, Literal::CodeIndex(_))) = terms.last() {
+                        if let Some(Term::Literal(_, Literal::CodeIndexOffset(_))) = terms.last() {
                             arg_terms
                                 .push(process_term(module_name, Term::Clause(cell, name, terms)));
 
@@ -453,7 +433,10 @@ fn build_meta_predicate_clause<'a, LS: LoadState<'a>>(
 
                         let idx = loader.get_or_insert_qualified_code_index(module_name, key);
 
-                        terms.push(Term::Literal(Cell::default(), Literal::CodeIndex(idx)));
+                        terms.push(Term::Literal(
+                            Cell::default(),
+                            Literal::CodeIndexOffset(idx.into()),
+                        ));
                         process_term(module_name, Term::Clause(cell, name, terms))
                     }
                     Term::Literal(cell, Literal::Atom(name)) => {
@@ -464,7 +447,10 @@ fn build_meta_predicate_clause<'a, LS: LoadState<'a>>(
                             Term::Clause(
                                 cell,
                                 name,
-                                vec![Term::Literal(Cell::default(), Literal::CodeIndex(idx))],
+                                vec![Term::Literal(
+                                    Cell::default(),
+                                    Literal::CodeIndexOffset(idx.into()),
+                                )],
                             ),
                         )
                     }
@@ -489,7 +475,7 @@ pub(super) fn clause_to_query_term<'a, LS: LoadState<'a>>(
     mut terms: Vec<Term>,
     call_policy: CallPolicy,
 ) -> QueryTerm {
-    if let Some(Term::Literal(_, Literal::CodeIndex(_))) = terms.last() {
+    if let Some(Term::Literal(_, Literal::CodeIndexOffset(_))) = terms.last() {
         // supplementary code vector indices are unnecessary for
         // root-level clauses.
         terms.pop();
@@ -524,7 +510,7 @@ pub(super) fn qualified_clause_to_query_term<'a, LS: LoadState<'a>>(
     mut terms: Vec<Term>,
     call_policy: CallPolicy,
 ) -> QueryTerm {
-    if let Some(Term::Literal(_, Literal::CodeIndex(_))) = terms.last() {
+    if let Some(Term::Literal(_, Literal::CodeIndexOffset(_))) = terms.last() {
         // supplementary code vector indices are unnecessary for
         // root-level clauses.
         terms.pop();
@@ -605,7 +591,7 @@ impl Preprocessor {
         &mut self,
         loader: &mut Loader<'a, LS>,
         term: Term,
-    ) -> Result<TopLevel, CompilationError> {
+    ) -> Result<PredicateClause, CompilationError> {
         match term {
             Term::Clause(r, name, mut terms) => {
                 let is_rule = name == atom!(":-") && terms.len() == 2;
@@ -615,16 +601,16 @@ impl Preprocessor {
                     let head = terms.pop().unwrap();
 
                     let (rule, var_data) = self.setup_rule(loader, head, tail)?;
-                    Ok(TopLevel::Rule(rule, var_data))
+                    Ok(PredicateClause::Rule(rule, var_data))
                 } else {
                     let term = Term::Clause(r, name, terms);
                     let (fact, var_data) = self.setup_fact(term)?;
-                    Ok(TopLevel::Fact(fact, var_data))
+                    Ok(PredicateClause::Fact(fact, var_data))
                 }
             }
             term => {
                 let (fact, var_data) = self.setup_fact(term)?;
-                Ok(TopLevel::Fact(fact, var_data))
+                Ok(PredicateClause::Fact(fact, var_data))
             }
         }
     }

src/machine/stack.rs

@@ -59,9 +59,10 @@ impl Index<usize> for AndFrame {
 
         unsafe {
             let ptr = self as *const crate::machine::stack::AndFrame as *const u8;
-            let ptr = ptr as usize + prelude_offset + index_offset;
 
-            &*(ptr as *const HeapCellValue)
+            // This address falls outside the provenance for self, therefore we have to get it
+            // from exposed provenance.
+            &*std::ptr::with_exposed_provenance(ptr.addr() + prelude_offset + index_offset)
         }
     }
 }
@@ -72,10 +73,11 @@ impl IndexMut<usize> for AndFrame {
         let index_offset = (index - 1) * mem::size_of::<HeapCellValue>();
 
         unsafe {
-            let ptr = self as *mut crate::machine::stack::AndFrame as *const u8;
+            let ptr = self as *mut crate::machine::stack::AndFrame as *mut u8;
-            let ptr = ptr as usize + prelude_offset + index_offset;
 
-            &mut *(ptr as *mut HeapCellValue)
+            // This address falls outside the provenance for self, therefore we have to get it
+            // from exposed provenance.
+            &mut *std::ptr::with_exposed_provenance_mut(ptr.addr() + prelude_offset + index_offset)
         }
     }
 }
@@ -85,20 +87,14 @@ impl Index<usize> for Stack {
 
     #[inline]
     fn index(&self, index: usize) -> &Self::Output {
-        unsafe {
+        unsafe { &*self.buf.base.add(index).cast() }
-            let ptr = self.buf.base as usize + index;
-            &*(ptr as *const HeapCellValue)
-        }
     }
 }
 
 impl IndexMut<usize> for Stack {
     #[inline]
     fn index_mut(&mut self, index: usize) -> &mut Self::Output {
-        unsafe {
+        unsafe { &mut *self.buf.base.add(index).cast_mut().cast() }
-            let ptr = self.buf.base as usize + index;
-            &mut *(ptr as *mut HeapCellValue)
-        }
     }
 }
 
@@ -132,9 +128,10 @@ impl Index<usize> for OrFrame {
 
         unsafe {
             let ptr = self as *const crate::machine::stack::OrFrame as *const u8;
-            let ptr = ptr as usize + prelude_offset + index_offset;
 
-            &*(ptr as *const HeapCellValue)
+            // This address falls outside the provenance for self, therefore we have to get it
+            // from exposed provenance.
+            &*std::ptr::with_exposed_provenance(ptr.addr() + prelude_offset + index_offset)
         }
     }
 }
@@ -146,10 +143,11 @@ impl IndexMut<usize> for OrFrame {
         let index_offset = index * mem::size_of::<HeapCellValue>();
 
         unsafe {
-            let ptr = self as *mut crate::machine::stack::OrFrame as *const u8;
+            let ptr = self as *mut crate::machine::stack::OrFrame as *mut u8;
-            let ptr = ptr as usize + prelude_offset + index_offset;
 
-            &mut *(ptr as *mut HeapCellValue)
+            // This address falls outside the provenance for self, therefore we have to get it
+            // from exposed provenance.
+            &mut *std::ptr::with_exposed_provenance_mut(ptr.addr() + prelude_offset + index_offset)
         }
     }
 }
@@ -187,15 +185,19 @@ impl Stack {
         let frame_size = AndFrame::size_of(num_cells);
 
         unsafe {
-            let e = (*self.buf.ptr.get_mut()) as usize - self.buf.base as usize;
+            let e = (*self.buf.ptr.get_mut()).addr() - self.buf.base.addr();
             let new_ptr = self.alloc(frame_size);
             let mut offset = prelude_size::<AndFramePrelude>();
 
             for idx in 0..num_cells {
-                ptr::write(
+                let cell_ptr = new_ptr.add(offset) as *mut HeapCellValue;
-                    new_ptr.add(offset) as *mut HeapCellValue,
+                ptr::write(cell_ptr, stack_loc_as_cell!(AndFrame, e, idx + 1));
-                    stack_loc_as_cell!(AndFrame, e, idx + 1),
+
-                );
+                // Because in the Index and IndexMut inplementations we need to get this from
+                // exposed provenance, we need to expose the provenance here, even though we don't
+                // actually use the value for anything. This is a reminder that `expose_provenance`
+                // isn't just a cast from a pointer to an integer but has actual side effects.
+                cell_ptr.expose_provenance();
 
                 offset += mem::size_of::<HeapCellValue>();
             }
@@ -208,22 +210,26 @@ impl Stack {
     }
 
     pub(crate) fn top(&self) -> usize {
-        unsafe { (*self.buf.ptr.get()) as usize - self.buf.base as usize }
+        unsafe { (*self.buf.ptr.get()).addr() - self.buf.base.addr() }
     }
 
     pub(crate) fn allocate_or_frame(&mut self, num_cells: usize) -> usize {
         let frame_size = OrFrame::size_of(num_cells);
 
         unsafe {
-            let b = (*self.buf.ptr.get_mut()) as usize - self.buf.base as usize;
+            let b = (*self.buf.ptr.get_mut()).addr() - self.buf.base.addr();
             let new_ptr = self.alloc(frame_size);
             let mut offset = prelude_size::<OrFramePrelude>();
 
             for idx in 0..num_cells {
-                ptr::write(
+                let cell_ptr = new_ptr.byte_add(offset) as *mut HeapCellValue;
-                    (new_ptr as usize + offset) as *mut HeapCellValue,
+                ptr::write(cell_ptr, stack_loc_as_cell!(OrFrame, b, idx));
-                    stack_loc_as_cell!(OrFrame, b, idx),
+
-                );
+                // Because in the Index and IndexMut inplementations we need to get this from
+                // exposed provenance, we need to expose the provenance here, even though we don't
+                // actually use the value for anything. This is a reminder that `expose_provenance`
+                // isn't just a cast from a pointer to an integer but has actual side effects.
+                cell_ptr.expose_provenance();
 
                 offset += mem::size_of::<HeapCellValue>();
             }
@@ -237,10 +243,7 @@ impl Stack {
 
     #[inline(always)]
     pub(crate) fn index_and_frame(&self, e: usize) -> &AndFrame {
-        unsafe {
+        unsafe { &*self.buf.base.add(e).cast() }
-            let ptr = self.buf.base as usize + e;
-            &*(ptr as *const AndFrame)
-        }
     }
 
     #[inline(always)]
@@ -254,26 +257,20 @@ impl Stack {
 
     #[inline(always)]
     pub(crate) fn index_or_frame(&self, b: usize) -> &OrFrame {
-        unsafe {
+        unsafe { &*self.buf.base.add(b).cast() }
-            let ptr = self.buf.base as usize + b;
-            &*(ptr as *const OrFrame)
-        }
     }
 
     #[inline(always)]
     pub(crate) fn index_or_frame_mut(&mut self, b: usize) -> &mut OrFrame {
-        unsafe {
+        unsafe { &mut *self.buf.base.add(b).cast_mut().cast() }
-            let ptr = self.buf.base as usize + b;
-            &mut *(ptr as *mut OrFrame)
-        }
     }
 
     #[inline(always)]
     pub(crate) fn truncate(&mut self, b: usize) {
-        let base = self.buf.base as usize + b;
+        let base = unsafe { self.buf.base.add(b) };
 
-        if base < (*self.buf.ptr.get_mut()) as usize {
+        if base < (*self.buf.ptr.get_mut()) {
-            *self.buf.ptr.get_mut() = base as *mut _;
+            *self.buf.ptr.get_mut() = base.cast_mut();
         }
     }
 }

src/machine/streams.rs

@@ -1,12 +1,12 @@
 use crate::arena::*;
 use crate::atom_table::*;
+use crate::functor_macro::*;
 use crate::parser::ast::*;
 use crate::parser::char_reader::*;
 use crate::read::*;
 
 #[cfg(feature = "http")]
 use crate::http::HttpResponse;
-use crate::machine::heap::*;
 use crate::machine::machine_errors::*;
 use crate::machine::machine_indices::*;
 use crate::machine::machine_state::*;
@@ -23,6 +23,8 @@ use std::fmt::Debug;
 use std::fs::{File, OpenOptions};
 use std::hash::Hash;
 use std::io;
+use std::io::PipeReader;
+use std::io::PipeWriter;
 use std::io::{Cursor, ErrorKind, Read, Seek, SeekFrom, Write};
 use std::mem::ManuallyDrop;
 use std::net::{Shutdown, TcpStream};
@@ -476,7 +478,7 @@ impl StreamOptions {
     #[inline]
     pub fn get_alias(self) -> Option<Atom> {
         if self.has_alias() {
-            Some(Atom::from(self.alias() << 3))
+            Some(Atom::from(self.alias()))
         } else {
             None
         }
@@ -487,7 +489,7 @@ impl StreamOptions {
         self.set_has_alias(alias.is_some());
 
         if let Some(alias) = alias {
-            self.set_alias(alias.flat_index());
+            self.set_alias(alias.index);
         }
     }
 }
@@ -588,6 +590,8 @@ arena_allocated_impl_for_stream!(StandardOutputStream, StandardOutputStream);
 arena_allocated_impl_for_stream!(StandardErrorStream, StandardErrorStream);
 arena_allocated_impl_for_stream!(CharReader<CallbackStream>, CallbackStream);
 arena_allocated_impl_for_stream!(CharReader<InputChannelStream>, InputChannelStream);
+arena_allocated_impl_for_stream!(CharReader<PipeReader>, PipeReader);
+arena_allocated_impl_for_stream!(CharReader<PipeWriter>, PipeWriter);
 
 #[derive(Debug, Copy, Clone)]
 pub enum Stream {
@@ -608,6 +612,8 @@ pub enum Stream {
     StandardError(TypedArenaPtr<StandardErrorStream>),
     Callback(TypedArenaPtr<CallbackStream>),
     InputChannel(TypedArenaPtr<InputChannelStream>),
+    PipeReader(TypedArenaPtr<PipeReader>),
+    PipeWriter(TypedArenaPtr<PipeWriter>),
 }
 
 impl From<TypedArenaPtr<ReadlineStream>> for Stream {
@@ -688,6 +694,8 @@ impl Stream {
             ArenaHeaderTag::InputChannelStream => {
                 Stream::InputChannel(unsafe { ptr.as_typed_ptr() })
             }
+            ArenaHeaderTag::PipeReader => Stream::PipeReader(unsafe { ptr.as_typed_ptr() }),
+            ArenaHeaderTag::PipeWriter => Stream::PipeWriter(unsafe { ptr.as_typed_ptr() }),
             _ => unreachable!(),
         }
     }
@@ -726,6 +734,8 @@ impl Stream {
             Stream::StandardError(ptr) => ptr.header_ptr(),
             Stream::Callback(ptr) => ptr.header_ptr(),
             Stream::InputChannel(ptr) => ptr.header_ptr(),
+            Stream::PipeReader(ptr) => ptr.header_ptr(),
+            Stream::PipeWriter(ptr) => ptr.header_ptr(),
         }
     }
 
@@ -748,6 +758,8 @@ impl Stream {
             Stream::StandardError(ref ptr) => &ptr.options,
             Stream::Callback(ref ptr) => &ptr.options,
             Stream::InputChannel(ref ptr) => &ptr.options,
+            Stream::PipeReader(ref ptr) => &ptr.options,
+            Stream::PipeWriter(ref ptr) => &ptr.options,
         }
     }
 
@@ -770,6 +782,8 @@ impl Stream {
             Stream::StandardError(ref mut ptr) => &mut ptr.options,
             Stream::Callback(ref mut ptr) => &mut ptr.options,
             Stream::InputChannel(ref mut ptr) => &mut ptr.options,
+            Stream::PipeReader(ref mut ptr) => &mut ptr.options,
+            Stream::PipeWriter(ref mut ptr) => &mut ptr.options,
         }
     }
 
@@ -793,6 +807,8 @@ impl Stream {
             Stream::StandardError(ptr) => ptr.lines_read += incr_num_lines_read,
             Stream::Callback(ptr) => ptr.lines_read += incr_num_lines_read,
             Stream::InputChannel(ptr) => ptr.lines_read += incr_num_lines_read,
+            Stream::PipeReader(ptr) => ptr.lines_read += incr_num_lines_read,
+            Stream::PipeWriter(_) => {}
         }
     }
 
@@ -816,6 +832,8 @@ impl Stream {
             Stream::StandardError(ptr) => ptr.lines_read = value,
             Stream::Callback(ptr) => ptr.lines_read = value,
             Stream::InputChannel(ptr) => ptr.lines_read = value,
+            Stream::PipeReader(ptr) => ptr.lines_read = value,
+            Stream::PipeWriter(_) => {}
         }
     }
 
@@ -839,6 +857,8 @@ impl Stream {
             Stream::StandardError(ptr) => ptr.lines_read,
             Stream::Callback(ptr) => ptr.lines_read,
             Stream::InputChannel(ptr) => ptr.lines_read,
+            Stream::PipeReader(ptr) => ptr.lines_read,
+            Stream::PipeWriter(_) => 0,
         }
     }
 }
@@ -856,6 +876,8 @@ impl CharRead for Stream {
             Stream::StaticString(src) => (*src).peek_char(),
             Stream::Byte(cursor) => (*cursor).peek_char(),
             Stream::InputChannel(cursor) => (*cursor).peek_char(),
+            Stream::PipeReader(cursor) => (*cursor).peek_char(),
+
             #[cfg(feature = "http")]
             Stream::HttpWrite(_) => Some(Err(std::io::Error::new(
                 ErrorKind::PermissionDenied,
@@ -865,7 +887,8 @@ impl CharRead for Stream {
             | Stream::StandardError(_)
             | Stream::StandardOutput(_)
             | Stream::Null(_)
-            | Stream::Callback(_) => Some(Err(std::io::Error::new(
+            | Stream::Callback(_)
+            | Stream::PipeWriter(_) => Some(Err(std::io::Error::new(
                 ErrorKind::PermissionDenied,
                 StreamError::ReadFromOutputStream,
             ))),
@@ -884,6 +907,7 @@ impl CharRead for Stream {
             Stream::StaticString(src) => (*src).read_char(),
             Stream::Byte(cursor) => (*cursor).read_char(),
             Stream::InputChannel(cursor) => (*cursor).read_char(),
+            Stream::PipeReader(cursor) => (*cursor).read_char(),
             #[cfg(feature = "http")]
             Stream::HttpWrite(_) => Some(Err(std::io::Error::new(
                 ErrorKind::PermissionDenied,
@@ -893,7 +917,8 @@ impl CharRead for Stream {
             | Stream::StandardError(_)
             | Stream::StandardOutput(_)
             | Stream::Null(_)
-            | Stream::Callback(_) => Some(Err(std::io::Error::new(
+            | Stream::Callback(_)
+            | Stream::PipeWriter(_) => Some(Err(std::io::Error::new(
                 ErrorKind::PermissionDenied,
                 StreamError::ReadFromOutputStream,
             ))),
@@ -911,13 +936,15 @@ impl CharRead for Stream {
             Stream::Readline(rl_stream) => rl_stream.put_back_char(c),
             Stream::StaticString(src) => src.put_back_char(c),
             Stream::Byte(cursor) => cursor.put_back_char(c),
+            Stream::PipeReader(cursor) => cursor.put_back_char(c),
             #[cfg(feature = "http")]
             Stream::HttpWrite(_) => {}
             Stream::OutputFile(_)
             | Stream::StandardError(_)
             | Stream::StandardOutput(_)
             | Stream::Null(_)
-            | Stream::Callback(_) => {}
+            | Stream::Callback(_)
+            | Stream::PipeWriter(_) => {}
             Stream::InputChannel(_) => {}
         }
     }
@@ -934,13 +961,15 @@ impl CharRead for Stream {
             Stream::StaticString(ref mut src) => src.consume(nread),
             Stream::Byte(ref mut cursor) => cursor.consume(nread),
             Stream::InputChannel(ref mut cursor) => cursor.consume(nread),
+            Stream::PipeReader(ref mut cursor) => cursor.consume(nread),
             #[cfg(feature = "http")]
             Stream::HttpWrite(_) => {}
             Stream::OutputFile(_)
             | Stream::StandardError(_)
             | Stream::StandardOutput(_)
             | Stream::Null(_)
-            | Stream::Callback(_) => {}
+            | Stream::Callback(_)
+            | Stream::PipeWriter(_) => {}
         }
     }
 }
@@ -959,6 +988,7 @@ impl Read for Stream {
             Stream::StaticString(src) => (*src).read(buf),
             Stream::Byte(cursor) => (*cursor).read(buf),
             Stream::InputChannel(cursor) => (*cursor).read(buf),
+            Stream::PipeReader(cursor) => (*cursor).read(buf),
             #[cfg(feature = "http")]
             Stream::HttpWrite(_) => Err(std::io::Error::new(
                 ErrorKind::PermissionDenied,
@@ -967,7 +997,8 @@ impl Read for Stream {
             Stream::OutputFile(_)
             | Stream::StandardError(_)
             | Stream::StandardOutput(_)
-            | Stream::Callback(_) => Err(std::io::Error::new(
+            | Stream::Callback(_)
+            | Stream::PipeWriter(_) => Err(std::io::Error::new(
                 ErrorKind::PermissionDenied,
                 StreamError::ReadFromOutputStream,
             )),
@@ -989,6 +1020,7 @@ impl Write for Stream {
             Stream::StandardError(stream) => stream.write(buf),
             #[cfg(feature = "http")]
             Stream::HttpWrite(ref mut stream) => stream.get_mut().write(buf),
+            Stream::PipeWriter(ref mut stream) => stream.get_mut().write(buf),
             #[cfg(feature = "http")]
             Stream::HttpRead(_) => Err(std::io::Error::new(
                 ErrorKind::PermissionDenied,
@@ -998,7 +1030,8 @@ impl Write for Stream {
             Stream::StaticString(_)
             | Stream::InputChannel(_)
             | Stream::Readline(_)
-            | Stream::InputFile(..) => Err(std::io::Error::new(
+            | Stream::InputFile(..)
+            | Stream::PipeReader(_) => Err(std::io::Error::new(
                 ErrorKind::PermissionDenied,
                 StreamError::WriteToInputStream,
             )),
@@ -1015,6 +1048,7 @@ impl Write for Stream {
             Stream::Callback(ref mut callback_stream) => callback_stream.stream.get_mut().flush(),
             Stream::StandardError(stream) => stream.stream.flush(),
             Stream::StandardOutput(stream) => stream.stream.flush(),
+            Stream::PipeWriter(ref mut stream) => stream.stream.get_mut().flush(),
             #[cfg(feature = "http")]
             Stream::HttpWrite(ref mut stream) => stream.stream.get_mut().flush(),
             #[cfg(feature = "http")]
@@ -1026,7 +1060,8 @@ impl Write for Stream {
             Stream::StaticString(_)
             | Stream::InputChannel(_)
             | Stream::Readline(_)
-            | Stream::InputFile(_) => Err(std::io::Error::new(
+            | Stream::InputFile(_)
+            | Stream::PipeReader(_) => Err(std::io::Error::new(
                 ErrorKind::PermissionDenied,
                 StreamError::FlushToInputStream,
             )),
@@ -1192,6 +1227,8 @@ impl Stream {
             Stream::StandardError(stream) => stream.past_end_of_stream,
             Stream::Callback(stream) => stream.past_end_of_stream,
             Stream::InputChannel(stream) => stream.past_end_of_stream,
+            Stream::PipeReader(stream) => stream.past_end_of_stream,
+            Stream::PipeWriter(stream) => stream.past_end_of_stream,
         }
     }
 
@@ -1220,6 +1257,8 @@ impl Stream {
             Stream::StandardError(stream) => stream.past_end_of_stream = value,
             Stream::Callback(stream) => stream.past_end_of_stream = value,
             Stream::InputChannel(stream) => stream.past_end_of_stream = value,
+            Stream::PipeReader(stream) => stream.past_end_of_stream = value,
+            Stream::PipeWriter(stream) => stream.past_end_of_stream = value,
         }
     }
 
@@ -1330,7 +1369,8 @@ impl Stream {
             | Stream::InputChannel(_)
             | Stream::Readline(_)
             | Stream::StaticString(_)
-            | Stream::InputFile(..) => atom!("read"),
+            | Stream::InputFile(..)
+            | Stream::PipeReader(_) => atom!("read"),
             Stream::NamedTcp(..) => atom!("read_append"),
             Stream::OutputFile(file) if file.is_append => atom!("append"),
             #[cfg(feature = "http")]
@@ -1338,7 +1378,8 @@ impl Stream {
             Stream::OutputFile(_)
             | Stream::StandardError(_)
             | Stream::StandardOutput(_)
-            | Stream::Callback(_) => {
+            | Stream::Callback(_)
+            | Stream::PipeWriter(_) => {
                 atom!("write")
             }
             Stream::Null(_) => atom!(""),
@@ -1372,6 +1413,20 @@ impl Stream {
         ))
     }
 
+    pub(crate) fn from_pipe_writer(writer: io::PipeWriter, arena: &mut Arena) -> Stream {
+        Stream::PipeWriter(arena_alloc!(
+            ManuallyDrop::new(StreamLayout::new(CharReader::new(writer))),
+            arena
+        ))
+    }
+
+    pub(crate) fn from_pipe_reader(reader: io::PipeReader, arena: &mut Arena) -> Stream {
+        Stream::PipeReader(arena_alloc!(
+            ManuallyDrop::new(StreamLayout::new(CharReader::new(reader))),
+            arena
+        ))
+    }
+
     #[inline]
     pub(crate) fn from_tcp_stream(address: Atom, tcp_stream: TcpStream, arena: &mut Arena) -> Self {
         tcp_stream.set_read_timeout(None).unwrap();
@@ -1512,6 +1567,16 @@ impl Stream {
                 Ok(())
             }
 
+            Stream::PipeReader(mut stream) => {
+                stream.drop_payload();
+                Ok(())
+            }
+
+            Stream::PipeWriter(mut stream) => {
+                stream.drop_payload();
+                Ok(())
+            }
+
             Stream::Null(_) => Ok(()),
 
             Stream::Readline(_) | Stream::StandardOutput(_) | Stream::StandardError(_) => {
@@ -1538,6 +1603,7 @@ impl Stream {
             | Stream::Readline(_)
             | Stream::StaticString(_)
             | Stream::InputFile(..)
+            | Stream::PipeReader(_)
             | Stream::Null(_) => true,
             _ => false,
         }
@@ -1556,6 +1622,7 @@ impl Stream {
             | Stream::Byte(_)
             | Stream::OutputFile(..)
             | Stream::Callback(_)
+            | Stream::PipeWriter(_)
             | Stream::Null(_) => true,
             _ => false,
         }
@@ -1653,7 +1720,8 @@ impl MachineState {
                 };
 
                 stream.set_past_end_of_stream(true);
-                Ok(unify!(self, result, end_of_stream))
+                unify!(self, result, end_of_stream);
+                Ok(())
             }
             EOFAction::Reset => {
                 if !stream.reset() {
@@ -1808,59 +1876,60 @@ impl MachineState {
         let addr = self.store(MachineState::deref(self, addr));
 
         read_heap_cell!(addr,
-                        (HeapCellValueTag::Atom, (name, arity)) => {
+            (HeapCellValueTag::Atom, (name, arity)) => {
-                            debug_assert_eq!(arity, 0);
+                debug_assert_eq!(arity, 0);
 
-                            return match indices.get_stream(name) {
+                return match indices.get_stream(name) {
-                                Some(stream) => Ok(stream),
+                    Some(stream) => Ok(stream),
-                                _ => {
+                    _ => {
-                                    let stub = functor_stub(caller, arity);
+                        let stub = functor_stub(caller, arity);
-                                    let addr = atom_as_cell!(name);
+                        let addr = atom_as_cell!(name);
 
-                                    let existence_error = self.existence_error(ExistenceError::Stream(addr));
+                        let existence_error = self.existence_error(ExistenceError::Stream(addr));
 
-                                    Err(self.error_form(existence_error, stub))
+                        Err(self.error_form(existence_error, stub))
-                                }
+                    }
-                            };
+                };
-                        }
+            }
-                        (HeapCellValueTag::Str, s) => {
+            (HeapCellValueTag::Str, s) => {
-                            let (name, arity) = cell_as_atom_cell!(self.heap[s])
+                let (name, arity) = cell_as_atom_cell!(self.heap[s])
-                                .get_name_and_arity();
+                    .get_name_and_arity();
 
-                            debug_assert_eq!(arity, 0);
+                debug_assert_eq!(arity, 0);
 
-                            return match indices.get_stream(name) {
+                return match indices.get_stream(name) {
-                                Some(stream) => Ok(stream),
+                    Some(stream) => Ok(stream),
-                                _ => {
+                    _ => {
-                                    let stub = functor_stub(caller, arity);
+                        let stub = functor_stub(caller, arity);
-                                    let addr = atom_as_cell!(name);
+                        let addr = atom_as_cell!(name);
 
-                                    let existence_error = self.existence_error(ExistenceError::Stream(addr));
+                        let existence_error = self.existence_error(ExistenceError::Stream(addr));
 
-                                    Err(self.error_form(existence_error, stub))
+                        Err(self.error_form(existence_error, stub))
-                                }
+                    }
-                            };
+                };
-                        }
+            }
-                        (HeapCellValueTag::Cons, ptr) => {
+            (HeapCellValueTag::Cons, ptr) => {
-                            match_untyped_arena_ptr!(ptr,
+                match_untyped_arena_ptr!(ptr,
-                                (ArenaHeaderTag::Stream, stream) => {
+                   (ArenaHeaderTag::Stream, stream) => {
-                                    if stream.is_null_stream() {
+                       return if stream.is_null_stream() {
-                                        unreachable!("Null streams have no Cons representation");
+                           Err(self.open_permission_error(stream_as_cell!(stream), caller, arity))
-                                    }
+                       } else {
-                                    return Ok(stream);
+                           Ok(stream)
-                                }
+                       };
-                                (ArenaHeaderTag::Dropped, _value) => {
+                   }
-                                    let stub = functor_stub(caller, arity);
+                   (ArenaHeaderTag::Dropped, _value) => {
-                                    let err = self.existence_error(ExistenceError::Stream(addr));
+                       let stub = functor_stub(caller, arity);
+                       let err = self.existence_error(ExistenceError::Stream(addr));
 
-                                    return Err(self.error_form(err, stub));
+                       return Err(self.error_form(err, stub));
-                                }
+                   }
-                                _ => {
+                   _ => {
-                                }
+                   }
-                            );
+                );
-                        }
+            }
-                        _ => {
+            _ => {
-                        }
+            }
         );
 
         let stub = functor_stub(caller, arity);
@@ -1953,7 +2022,7 @@ impl MachineState {
         let err = self.permission_error(
             Permission::Open,
             atom!("source_sink"),
-            functor!(atom!("alias"), [atom(alias)]),
+            functor!(atom!("alias"), [atom_as_cell(alias)]),
         );
 
         self.error_form(err, stub)
@@ -1961,7 +2030,7 @@ impl MachineState {
 
     pub(crate) fn reposition_error(&mut self, stub_name: Atom, stub_arity: usize) -> MachineStub {
         let stub = functor_stub(stub_name, stub_arity);
-        let rep_stub = functor!(atom!("reposition"), [atom(atom!("true"))]);
+        let rep_stub = functor!(atom!("reposition"), [atom_as_cell((atom!("true")))]);
         let err = self.permission_error(Permission::Open, atom!("source_sink"), rep_stub);
 
         self.error_form(err, stub)
@@ -2086,7 +2155,7 @@ impl MachineState {
                         _ => {
                             // assume the OS is out of file descriptors.
                             let stub = functor_stub(atom!("open"), 4);
-                            let err = self.resource_error(ResourceError::OutOfFiles);
+                            let err = Self::resource_error(ResourceError::OutOfFiles);
 
                             return Err(self.error_form(err, stub));
                         }

src/machine/term_stream.rs

@@ -4,6 +4,7 @@ use crate::machine::loader::*;
 use crate::machine::machine_errors::*;
 use crate::machine::*;
 use crate::parser::ast::*;
+use crate::parser::lexer::*;
 use crate::parser::parser::*;
 use crate::read::devour_whitespace;
 
@@ -61,7 +62,7 @@ impl<'a> TermStream for BootstrappingTermStream<'a> {
 
     #[inline]
     fn eof(&mut self) -> Result<bool, CompilationError> {
-        devour_whitespace(&mut self.parser) // eliminate dangling comments before checking for EOF.
+        devour_whitespace(&mut self.parser.lexer) // eliminate dangling comments before checking for EOF.
             .map_err(CompilationError::from)
     }
 

src/machine/unify.rs

@@ -2,11 +2,10 @@ use crate::arena::*;
 use crate::forms::*;
 use crate::heap_iter::{stackful_preorder_iter, NonListElider};
 use crate::machine::machine_state::*;
-use crate::machine::partial_string::*;
 use crate::machine::*;
+use crate::offset_table::*;
 use crate::types::*;
 
-use std::cmp::Ordering;
 use std::ops::{Deref, DerefMut};
 
 use derive_more::*;
@@ -14,6 +13,18 @@ use fxhash::FxBuildHasher;
 use indexmap::IndexSet;
 use num_order::NumOrd;
 
+impl MachineState {
+    pub(crate) fn partial_string_to_pdl(&mut self, pstr_loc: usize, l: usize) {
+        let (c, succ_cell) = self.heap.last_str_char_and_tail(pstr_loc);
+
+        self.pdl.push(heap_loc_as_cell!(l + 1));
+        self.pdl.push(succ_cell);
+
+        self.pdl.push(heap_loc_as_cell!(l));
+        self.pdl.push(char_as_cell!(c));
+    }
+}
+
 pub(crate) trait Unifier: DerefMut<Target = MachineState> {
     fn unify_structure(&mut self, s1: usize, value: HeapCellValue) {
         // s1 is the value of a STR cell.
@@ -82,8 +93,8 @@ pub(crate) trait Unifier: DerefMut<Target = MachineState> {
                     self.fail = true;
                 }
             }
-            (HeapCellValueTag::PStrLoc | HeapCellValueTag::CStr | HeapCellValueTag::PStr) => {
+            (HeapCellValueTag::PStrLoc, l) => {
-                Self::unify_partial_string(self, list_loc_as_cell!(l1), value)
+                Self::unify_partial_string(self, l, list_loc_as_cell!(l1))
             }
             (HeapCellValueTag::AttrVar, h) => {
                 Self::bind(self, Ref::attr_var(h), list_loc_as_cell!(l1));
@@ -100,261 +111,43 @@ pub(crate) trait Unifier: DerefMut<Target = MachineState> {
         );
     }
 
-    fn unify_complete_string(&mut self, atom: Atom, value: HeapCellValue) {
+    fn unify_partial_string(&mut self, pstr_loc: usize, value: HeapCellValue) {
         if let Some(r) = value.as_var() {
-            if atom == atom!("") {
+            Self::bind(self, r, pstr_loc_as_cell!(pstr_loc));
-                Self::bind(self, r, atom_as_cell!(atom!("[]")));
-            } else {
-                Self::bind(self, r, atom_as_cstr_cell!(atom));
-            }
-
-            return;
-        }
-
-        read_heap_cell!(value,
-            (HeapCellValueTag::Atom, (cstr_atom, arity)) if atom == atom!("") => {
-                debug_assert_eq!(arity, 0);
-                self.fail = cstr_atom != atom!("[]");
-            }
-            (HeapCellValueTag::Str, s) => {
-                let (name, arity) = cell_as_atom_cell!(self.heap[s])
-                    .get_name_and_arity();
-
-                if arity == 0 {
-                    self.fail = atom == atom!("") && name != atom!("[]");
-                } else {
-                    // this is intentionally the same policy for
-                    // value.tag() == Lis and PStrLoc. they're not
-                    // grouped together to allow for arity == 0.
-                    Self::unify_partial_string(self, atom_as_cstr_cell!(atom), value);
-
-                    if !self.pdl.is_empty() {
-                        Self::unify_internal(self);
-                    }
-                }
-            }
-            (HeapCellValueTag::CStr, cstr_atom) => {
-                self.fail = atom != cstr_atom;
-            }
-            (HeapCellValueTag::Lis | HeapCellValueTag::PStrLoc) => {
-                Self::unify_partial_string(self, atom_as_cstr_cell!(atom), value);
-
-                if !self.pdl.is_empty() {
-                    Self::unify_internal(self);
-                }
-            }
-            _ => {
-                self.fail = true;
-            }
-        );
-    }
-
-    // the return value of unify_partial_string is interpreted as
-    // follows:
-    //
-    // Some(None) -- the strings are equal, nothing to unify
-    // Some(Some(f2,f1)) -- prefixes equal, try to unify focus values f2, f1
-    // None -- prefixes not equal, unification fails
-    //
-    // d1's tag is assumed to be one of LIS, STR or PSTRLOC.
-    fn unify_partial_string(&mut self, value_1: HeapCellValue, value_2: HeapCellValue) {
-        if let Some(r) = value_2.as_var() {
-            Self::bind(self, r, value_1);
             return;
         }
 
         let machine_st = self.deref_mut();
 
-        let s1 = machine_st.heap.len();
+        read_heap_cell!(value,
+            (HeapCellValueTag::Str, s) => {
+                let (name, arity) = cell_as_atom_cell!(machine_st.heap[s])
+                    .get_name_and_arity();
 
-        machine_st.heap.push(value_1);
+                if name == atom!(".") && arity == 2 {
-        machine_st.heap.push(value_2);
+                    machine_st.partial_string_to_pdl(pstr_loc, s+1);
-
-        let mut pstr_iter1 = HeapPStrIter::new(&machine_st.heap, s1);
-        let mut pstr_iter2 = HeapPStrIter::new(&machine_st.heap, s1 + 1);
-
-        fn unify_sequence(
-            machine_st: &mut MachineState,
-            iter: PStrIteratee,
-            source_cell: HeapCellValue,
-        ) -> bool {
-            match iter {
-                PStrIteratee::Char(focus, _) => {
-                    machine_st.pdl.push(machine_st.heap[focus]);
-                    machine_st.pdl.push(source_cell);
-                }
-                PStrIteratee::PStrSegment(focus, _, n) => {
-                    read_heap_cell!(machine_st.heap[focus],
-                        (HeapCellValueTag::CStr | HeapCellValueTag::PStr, pstr_atom) => {
-                            if focus < machine_st.heap.len() - 2 {
-                                machine_st.heap.pop();
-                                machine_st.heap.pop();
-                            }
-
-                            if n == 0 {
-                                let target_cell = match machine_st.heap[focus].get_tag() {
-                                    HeapCellValueTag::CStr => {
-                                        atom_as_cstr_cell!(pstr_atom)
-                                    }
-                                    HeapCellValueTag::PStr => {
-                                        pstr_loc_as_cell!(focus)
-                                    }
-                                    _ => {
-                                        unreachable!()
-                                    }
-                                };
-
-                                machine_st.pdl.push(target_cell);
-                                machine_st.pdl.push(source_cell);
-                            } else {
-                                let h_len = machine_st.heap.len();
-
-                                machine_st.heap.push(pstr_offset_as_cell!(focus));
-                                machine_st.heap.push(fixnum_as_cell!(
-                                    Fixnum::build_with(n as i64)
-                                ));
-
-                                machine_st.pdl.push(pstr_loc_as_cell!(h_len));
-                                machine_st.pdl.push(source_cell);
-                            }
-
-                            return true;
-                        }
-                        (HeapCellValueTag::PStrOffset, pstr_loc) => {
-                            let n0 = cell_as_fixnum!(machine_st.heap[focus+1])
-                                .get_num() as usize;
-
-                            if pstr_loc < machine_st.heap.len() - 2 {
-                                machine_st.heap.pop();
-                                machine_st.heap.pop();
-                            }
-
-                            if n == n0 {
-                                machine_st.pdl.push(pstr_loc_as_cell!(focus));
-                                machine_st.pdl.push(source_cell);
-                            } else {
-                                let h_len = machine_st.heap.len();
-
-                                machine_st.heap.push(pstr_offset_as_cell!(pstr_loc));
-                                machine_st.heap.push(fixnum_as_cell!(
-                                    Fixnum::build_with(n as i64)
-                                ));
-
-                                machine_st.pdl.push(pstr_loc_as_cell!(h_len));
-                                machine_st.pdl.push(source_cell);
-                            }
-
-                            return true;
-                        }
-                        _ => {
-                        }
-                    );
-
-                    if focus < machine_st.heap.len() - 2 {
-                        machine_st.heap.pop();
-                        machine_st.heap.pop();
-                    }
-
-                    machine_st.pdl.push(machine_st.heap[focus]);
-                    machine_st.pdl.push(source_cell);
-
-                    return true;
-                }
-            }
-
-            false
-        }
-
-        match compare_pstr_prefixes(&mut pstr_iter1, &mut pstr_iter2) {
-            PStrCmpResult::Ordered(Ordering::Equal) => {}
-            PStrCmpResult::Ordered(Ordering::Less) => {
-                if pstr_iter2.focus.as_var().is_none() {
-                    machine_st.fail = true;
                 } else {
-                    machine_st.pdl.push(empty_list_as_cell!());
-                    machine_st.pdl.push(pstr_iter2.focus);
-                }
-            }
-            PStrCmpResult::Ordered(Ordering::Greater) => {
-                if pstr_iter1.focus.as_var().is_none() {
                     machine_st.fail = true;
-                } else {
-                    machine_st.pdl.push(empty_list_as_cell!());
-                    machine_st.pdl.push(pstr_iter1.focus);
                 }
             }
-            continuable @ PStrCmpResult::FirstIterContinuable(iteratee)
+            (HeapCellValueTag::Lis, l) => {
-            | continuable @ PStrCmpResult::SecondIterContinuable(iteratee) => {
+                machine_st.partial_string_to_pdl(pstr_loc, l);
-                if continuable.is_second_iter() {
+            }
-                    std::mem::swap(&mut pstr_iter1, &mut pstr_iter2);
+            (HeapCellValueTag::PStrLoc, other_pstr_loc) => {
-                }
+                match machine_st.heap.compare_pstr_segments(pstr_loc, other_pstr_loc) {
-
+                    PStrSegmentCmpResult::Continue(v1, v2) => {
-                let mut chars_iter = PStrCharsIter {
+                        machine_st.pdl.push(v1.offset_by(pstr_loc));
-                    iter: pstr_iter1,
+                        machine_st.pdl.push(v2.offset_by(other_pstr_loc));
-                    item: Some(iteratee),
+                    }
-                };
+                    _ => {
-
+                        machine_st.fail = true;
-                let mut focus = pstr_iter2.focus;
-
-                'outer: {
-                    while let Some(c) = chars_iter.peek() {
-                        read_heap_cell!(focus,
-                            (HeapCellValueTag::Lis, l) => {
-                                let val = pstr_iter2.heap[l];
-
-                                machine_st.pdl.push(val);
-                                machine_st.pdl.push(char_as_cell!(c));
-
-                                focus = pstr_iter2.heap[l+1];
-                            }
-                            (HeapCellValueTag::Str, s) => {
-                                let (name, arity) = cell_as_atom_cell!(pstr_iter2.heap[s])
-                                    .get_name_and_arity();
-
-                                if name == atom!(".") && arity == 2 {
-                                    machine_st.pdl.push(pstr_iter2.heap[s+1]);
-                                    machine_st.pdl.push(char_as_cell!(c));
-
-                                    focus = pstr_iter2.heap[s+2];
-                                } else {
-                                    machine_st.fail = true;
-                                    break 'outer;
-                                }
-                            }
-                            (HeapCellValueTag::CStr | HeapCellValueTag::PStrLoc) => {
-                                unify_sequence(machine_st, chars_iter.item.unwrap(), focus);
-                                return;
-                            }
-                            (HeapCellValueTag::AttrVar | HeapCellValueTag::Var, h) => {
-                                if unify_sequence(machine_st, chars_iter.item.unwrap(), heap_loc_as_cell!(h)) {
-                                    return;
-                                }
-
-                                break 'outer;
-                            }
-                            _ => {
-                                machine_st.fail = true;
-                                break 'outer;
-                            }
-                        );
-
-                        chars_iter.next();
                     }
-
-                    chars_iter.iter.next();
-
-                    machine_st.pdl.push(focus);
-                    machine_st.pdl.push(chars_iter.iter.focus);
                 }
             }
-            PStrCmpResult::Unordered => {
+            _ => {
-                machine_st.pdl.push(pstr_iter1.focus);
+                machine_st.fail = true;
-                machine_st.pdl.push(pstr_iter2.focus);
             }
-        }
+        );
-
-        machine_st.heap.pop();
-        machine_st.heap.pop();
     }
 
     fn unify_atom(&mut self, atom: Atom, value: HeapCellValue) {
@@ -368,16 +161,6 @@ pub(crate) trait Unifier: DerefMut<Target = MachineState> {
 
                 self.fail = !(arity == 0 && name == atom);
             }
-            (HeapCellValueTag::CStr, cstr_atom) if atom == atom!("[]") => {
-                self.fail = cstr_atom != atom!("");
-            }
-            (HeapCellValueTag::Char, c1) => {
-                if let Some(c2) = atom.as_char() {
-                    self.fail = c1 != c2;
-                } else {
-                    self.fail = true;
-                }
-            }
             (HeapCellValueTag::AttrVar, h) => {
                 Self::bind(self, Ref::attr_var(h), atom_as_cell!(atom));
             }
@@ -412,11 +195,6 @@ pub(crate) trait Unifier: DerefMut<Target = MachineState> {
                     self.fail = true;
                 }
             }
-            (HeapCellValueTag::Char, c2) => {
-                if c != c2 {
-                    self.fail = true;
-                }
-            }
             (HeapCellValueTag::AttrVar, h) => {
                 Self::bind(self, Ref::attr_var(h), char_as_cell!(c));
             }
@@ -438,7 +216,9 @@ pub(crate) trait Unifier: DerefMut<Target = MachineState> {
             return;
         }
 
-        match Number::try_from(value) {
+        let machine_st = self.deref();
+
+        match Number::try_from((value, &machine_st.arena.f64_tbl)) {
             Ok(n2) => match n2 {
                 Number::Fixnum(n2) if n1.get_num() == n2.get_num() => {}
                 Number::Integer(n2) if (*n2).num_eq(&n1.get_num()) => {}
@@ -459,7 +239,9 @@ pub(crate) trait Unifier: DerefMut<Target = MachineState> {
             return;
         }
 
-        match Number::try_from(value) {
+        let machine_st = self.deref();
+
+        match Number::try_from((value, &machine_st.arena.f64_tbl)) {
             Ok(n2) => match n2 {
                 Number::Fixnum(n2) if (*n1).num_eq(&n2.get_num()) => {}
                 Number::Integer(n2) if (*n1).num_eq(&*n2) => {}
@@ -480,7 +262,9 @@ pub(crate) trait Unifier: DerefMut<Target = MachineState> {
             return;
         }
 
-        match Number::try_from(value) {
+        let machine_st = self.deref_mut();
+
+        match Number::try_from((value, &machine_st.arena.f64_tbl)) {
             Ok(n2) => match n2 {
                 Number::Fixnum(n2) if (*n1).num_eq(&Integer::from(n2.get_num())) => {}
                 Number::Integer(n2) if (*n1).num_eq(&*n2) => {}
@@ -495,15 +279,20 @@ pub(crate) trait Unifier: DerefMut<Target = MachineState> {
         }
     }
 
-    fn unify_f64(&mut self, f1: F64Ptr, value: HeapCellValue) {
+    fn unify_f64(&mut self, f1: F64Offset, value: HeapCellValue) {
         if let Some(r) = value.as_var() {
             Self::bind(self, r, HeapCellValue::from(f1));
             return;
         }
 
         read_heap_cell!(value,
-            (HeapCellValueTag::F64, f2) => {
+            (HeapCellValueTag::F64Offset, f2) => {
-                self.fail = **f1 != **f2;
+                let machine_st = self.deref_mut();
+
+                let f1 = machine_st.arena.f64_tbl.get_entry(f1);
+                let f2 = machine_st.arena.f64_tbl.get_entry(f2);
+
+                self.fail = f1 != f2;
             }
             _ => {
                 self.fail = true;
@@ -610,7 +399,7 @@ pub(crate) trait Unifier: DerefMut<Target = MachineState> {
                             tabu_list.insert((d1, d2));
                         }
                     }
-                    (HeapCellValueTag::PStrLoc) => {
+                    (HeapCellValueTag::PStrLoc, l) => {
                         read_heap_cell!(d2,
                             (HeapCellValueTag::PStrLoc |
                              HeapCellValueTag::Lis |
@@ -619,8 +408,7 @@ pub(crate) trait Unifier: DerefMut<Target = MachineState> {
                                     continue;
                                 }
                             }
-                            (HeapCellValueTag::CStr |
+                            (HeapCellValueTag::AttrVar |
-                             HeapCellValueTag::AttrVar |
                              HeapCellValueTag::Var |
                              HeapCellValueTag::StackVar) => {
                             }
@@ -630,52 +418,19 @@ pub(crate) trait Unifier: DerefMut<Target = MachineState> {
                             }
                         );
 
-                        Self::unify_partial_string(self, d1, d2);
+                        Self::unify_partial_string(self, l, d2);
 
                         if !self.fail && !d2.is_constant() {
                             let d2 = self.store(d2);
                             tabu_list.insert((d1, d2));
                         }
                     }
-                    (HeapCellValueTag::CStr) => {
+                    (HeapCellValueTag::F64Offset, f1) => {
-                        read_heap_cell!(d2,
-                            (HeapCellValueTag::AttrVar, h) => {
-                                Self::bind(self, Ref::attr_var(h), d1);
-                                continue;
-                            }
-                            (HeapCellValueTag::Var, h) => {
-                                Self::bind(self, Ref::heap_cell(h), d1);
-                                continue;
-                            }
-                            (HeapCellValueTag::StackVar, s) => {
-                                Self::bind(self, Ref::stack_cell(s), d1);
-                                continue;
-                            }
-                            (HeapCellValueTag::Str |
-                             HeapCellValueTag::Lis |
-                             HeapCellValueTag::PStrLoc) => {
-                            }
-                            (HeapCellValueTag::CStr) => {
-                                self.fail = d1 != d2;
-                                continue;
-                            }
-                            _ => {
-                                self.fail = true;
-                                return;
-                            }
-                        );
-
-                        Self::unify_partial_string(self, d2, d1);
-                    }
-                    (HeapCellValueTag::F64, f1) => {
                         Self::unify_f64(self, f1, d2);
                     }
                     (HeapCellValueTag::Fixnum, n1) => {
                         Self::unify_fixnum(self, n1, d2);
                     }
-                    (HeapCellValueTag::Char, c1) => {
-                        Self::unify_char(self, c1, d2);
-                    }
                     (HeapCellValueTag::Cons, ptr_1) => {
                         Self::unify_constant(self, ptr_1, d2);
                     }
@@ -707,12 +462,11 @@ fn bind_with_occurs_check<U: Unifier>(unifier: &mut U, r: Ref, value: HeapCellVa
 
     if !value.is_constant() {
         let machine_st: &mut MachineState = unifier.deref_mut();
+        machine_st.heap[0] = value;
 
-        for cell in stackful_preorder_iter::<NonListElider>(
+        for cell in
-            &mut machine_st.heap,
+            stackful_preorder_iter::<NonListElider>(&mut machine_st.heap, &mut machine_st.stack, 0)
-            &mut machine_st.stack,
+        {
-            value,
-        ) {
             let cell = unmark_cell_bits!(cell);
 
             if let Some(inner_r) = cell.as_var() {

src/macros.rs

@@ -1,15 +1,10 @@
 /* A simple macro to count the arguments in a variadic list
  * of token trees.
  */
-macro_rules! count_tt {
-    () => { 0 };
-    ($odd:tt $($a:tt $b:tt)*) => { (count_tt!($($a)*) << 1) | 1 };
-    ($($a:tt $even:tt)*) => { count_tt!($($a)*) << 1 };
-}
 
 macro_rules! char_as_cell {
     ($c: expr) => {
-        HeapCellValue::build_with(HeapCellValueTag::Char, $c as u64)
+        HeapCellValue::from_bytes(AtomCell::new_char_inlined($c).into_bytes())
     };
 }
 
@@ -19,12 +14,6 @@ macro_rules! fixnum_as_cell {
     };
 }
 
-macro_rules! cell_as_fixnum {
-    ($cell:expr) => {
-        Fixnum::from_bytes($cell.into_bytes())
-    };
-}
-
 macro_rules! integer_as_cell {
     ($n: expr) => {{
         match $n {
@@ -45,31 +34,17 @@ macro_rules! empty_list_as_cell {
 
 macro_rules! atom_as_cell {
     ($atom:expr) => {
-        HeapCellValue::from_bytes(
+        HeapCellValue::from_bytes(AtomCell::build_with($atom.index, 0).into_bytes())
-            AtomCell::build_with($atom.flat_index(), 0, HeapCellValueTag::Atom).into_bytes(),
-        )
     };
     ($atom:expr, $arity:expr) => {
-        HeapCellValue::from_bytes(
+        HeapCellValue::from_bytes(AtomCell::build_with($atom.index, $arity as u8).into_bytes())
-            AtomCell::build_with($atom.flat_index(), $arity as u16, HeapCellValueTag::Atom)
-                .into_bytes(),
-        )
-    };
-}
-
-macro_rules! cell_as_string {
-    ($cell:expr) => {
-        PartialString::from(cell_as_atom!($cell))
     };
 }
 
 macro_rules! cell_as_atom {
-    ($cell:expr) => {{
+    ($cell:expr) => {
-        let cell = AtomCell::from_bytes($cell.into_bytes());
+        AtomCell::from_bytes($cell.into_bytes()).get_name()
-        let name = (cell.get_index() as u64) << 3;
+    };
-
-        Atom::from(name)
-    }};
 }
 
 macro_rules! cell_as_atom_cell {
@@ -78,10 +53,17 @@ macro_rules! cell_as_atom_cell {
     };
 }
 
-macro_rules! cell_as_f64_ptr {
+macro_rules! cell_as_f64_offset {
     ($cell:expr) => {{
         let offset = $cell.get_value() as usize;
-        F64Ptr::from_offset(F64Offset::new(offset))
+        F64Offset::from(offset)
+    }};
+}
+
+macro_rules! cell_as_code_index_offset {
+    ($cell:expr) => {{
+        let offset = $cell.get_value() as usize;
+        CodeIndexOffset::from(offset)
     }};
 }
 
@@ -91,26 +73,12 @@ macro_rules! cell_as_untyped_arena_ptr {
     };
 }
 
-macro_rules! pstr_as_cell {
-    ($atom:expr) => {
-        HeapCellValue::from_bytes(
-            AtomCell::build_with($atom.flat_index(), 0, HeapCellValueTag::PStr).into_bytes(),
-        )
-    };
-}
-
 macro_rules! pstr_loc_as_cell {
     ($h:expr) => {
         HeapCellValue::build_with(HeapCellValueTag::PStrLoc, $h as u64)
     };
 }
 
-macro_rules! pstr_offset_as_cell {
-    ($h:expr) => {
-        HeapCellValue::build_with(HeapCellValueTag::PStrOffset, $h as u64)
-    };
-}
-
 macro_rules! list_loc_as_cell {
     ($h:expr) => {
         HeapCellValue::build_with(HeapCellValueTag::Lis, $h as u64)
@@ -172,11 +140,11 @@ macro_rules! typed_arena_ptr_as_cell {
 macro_rules! raw_ptr_as_cell {
     ($ptr:expr) => {{
         // Cell is 64-bit, but raw ptr is 32-bit in 32-bit systems
-        // TODO use <*{const,mut} _>::addr instead of as when the strict_provenance feature is stable rust-lang/rust#95228
+        let ptr: *const _ = $ptr;
-        // we might need <*{const,mut} _>::expose_provenance for strict provenance, dependening on how we recreate a pointer later
+        // This needs to expose provenance because it needs to be turned back into a pointer
-        let ptr : *const _ = $ptr;
+        // in contexts where there is no available provenance locally. For example, in
-        debug_assert!(!$ptr.is_null());
+        // `ConsPtr::as_ptr`.
-        HeapCellValue::from_ptr_addr(ptr as usize)
+        HeapCellValue::from_ptr_addr(ptr.expose_provenance())
     }};
 }
 
@@ -186,36 +154,10 @@ macro_rules! untyped_arena_ptr_as_cell {
     };
 }
 
-macro_rules! atom_as_cstr_cell {
+macro_rules! stream_as_cell {
-    ($atom:expr) => {{
+    ($ptr:expr) => {
-        let offset = $atom.flat_index();
+        raw_ptr_as_cell!($ptr.as_ptr())
-
+    };
-        HeapCellValue::from_bytes(
-            AtomCell::build_with(offset as u64, 0, HeapCellValueTag::CStr).into_bytes(),
-        )
-    }};
-}
-
-macro_rules! string_as_cstr_cell {
-    ($ptr:expr) => {{
-        let atom: Atom = $ptr.into();
-        let offset = atom.flat_index();
-
-        HeapCellValue::from_bytes(
-            AtomCell::build_with(offset as u64, 0, HeapCellValueTag::CStr).into_bytes(),
-        )
-    }};
-}
-
-macro_rules! string_as_pstr_cell {
-    ($ptr:expr) => {{
-        let atom: Atom = $ptr.into();
-        let offset = atom.flat_index();
-
-        HeapCellValue::from_bytes(
-            AtomCell::build_with(offset as u64, 0, HeapCellValueTag::PStr).into_bytes(),
-        )
-    }};
 }
 
 macro_rules! cell_as_stream {
@@ -276,9 +218,21 @@ macro_rules! match_untyped_arena_ptr_pat_body {
         #[allow(unused_braces)]
         $code
     }};
-    ($ptr:ident, IndexPtr, $ip:ident, $code:expr) => {{
+    ($ptr:ident, PipeReader, $listener:ident, $code:expr) => {{
         #[allow(unused_mut)]
-        let mut $ip = unsafe { $ptr.as_typed_ptr::<IndexPtr>() };
+        let mut $listener = unsafe { $ptr.as_typed_ptr::<PipeReader>() };
+        #[allow(unused_braces)]
+        $code
+    }};
+    ($ptr:ident, PipeWriter, $listener:ident, $code:expr) => {{
+        #[allow(unused_mut)]
+        let mut $listener = unsafe { $ptr.as_typed_ptr::<PipeWriter>() };
+        #[allow(unused_braces)]
+        $code
+    }};
+    ($ptr:ident, ChildProcess, $listener:ident, $code:expr) => {{
+        #[allow(unused_mut)]
+        let mut $listener = unsafe { $ptr.as_typed_ptr::<std::process::Child>() };
         #[allow(unused_braces)]
         $code
     }};
@@ -304,12 +258,8 @@ macro_rules! match_untyped_arena_ptr_pat {
             | ArenaHeaderTag::InputChannelStream
             | ArenaHeaderTag::StandardOutputStream
             | ArenaHeaderTag::StandardErrorStream
-    };
+            | ArenaHeaderTag::PipeReader
-    (IndexPtr) => {
+            | ArenaHeaderTag::PipeWriter
-        ArenaHeaderTag::IndexPtrUndefined
-            | ArenaHeaderTag::IndexPtrDynamicUndefined
-            | ArenaHeaderTag::IndexPtrDynamicIndex
-            | ArenaHeaderTag::IndexPtrIndex
     };
     ($tag:ident) => {
         ArenaHeaderTag::$tag
@@ -336,8 +286,13 @@ macro_rules! read_heap_cell_pat_body {
         #[allow(unused_braces)]
         $code
     }};
-    ($cell:ident, F64, $n:ident, $code:expr) => {{
+    ($cell:ident, F64Offset, $n:ident, $code:expr) => {{
-        let $n = cell_as_f64_ptr!($cell);
+        let $n = cell_as_f64_offset!($cell);
+        #[allow(unused_braces)]
+        $code
+    }};
+    ($cell:ident, CodeIndexOffset, $n:ident, $code:expr) => {{
+        let $n = cell_as_code_index_offset!($cell);
         #[allow(unused_braces)]
         $code
     }};
@@ -346,26 +301,6 @@ macro_rules! read_heap_cell_pat_body {
         #[allow(unused_braces)]
         $code
     }};
-    ($cell:ident, PStr, $atom:ident, $code:expr) => {{
-        let $atom = cell_as_atom!($cell);
-        #[allow(unused_braces)]
-        $code
-    }};
-    ($cell:ident, CStr, $atom:ident, $code:expr) => {{
-        let $atom = cell_as_atom!($cell);
-        #[allow(unused_braces)]
-        $code
-    }};
-    ($cell:ident, CStr | PStr, $atom:ident, $code:expr) => {{
-        let $atom = cell_as_atom!($cell);
-        #[allow(unused_braces)]
-        $code
-    }};
-    ($cell:ident, PStr | CStr, $atom:ident, $code:expr) => {{
-        let $atom = cell_as_atom!($cell);
-        #[allow(unused_braces)]
-        $code
-    }};
     ($cell:ident, Fixnum, $value:ident, $code:expr) => {{
         let $value = Fixnum::from_bytes($cell.into_bytes());
         #[allow(unused_braces)]
@@ -386,11 +321,6 @@ macro_rules! read_heap_cell_pat_body {
         #[allow(unused_braces)]
         $code
     }};
-    ($cell:ident, Char, $value:ident, $code:expr) => {{
-        let $value = unsafe { char::from_u32_unchecked($cell.get_value() as u32) };
-        #[allow(unused_braces)]
-        $code
-    }};
     ($cell:ident, $($tags:tt)|+, $value:ident, $code:expr) => {{
         let $value = $cell.get_value() as usize;
         #[allow(unused_braces)]
@@ -432,119 +362,6 @@ macro_rules! read_heap_cell {
     });
 }
 
-macro_rules! functor {
-    ($name:expr, [$($dt:ident($($value:expr),*)),+], [$($aux:ident),*]) => ({
-        {
-            #[allow(unused_variables, unused_mut)]
-            let mut addendum = Heap::new();
-            let arity: usize = count_tt!($($dt) +);
-
-            #[allow(unused_variables)]
-            let aux_lens: [usize; count_tt!($($aux) *)] = [$($aux.len()),*];
-
-            let mut result =
-                vec![ atom_as_cell!($name, arity as u16),
-                      $(functor_term!( $dt($($value),*), arity, aux_lens, addendum ),)+ ];
-
-            $(
-                result.extend($aux.iter());
-            )*
-
-            result.extend(addendum.into_iter());
-            result
-        }
-    });
-    ($name:expr, [$($dt:ident($($value:expr),*)),+]) => ({
-        {
-            let arity: usize = count_tt!($($dt) +);
-
-            #[allow(unused_variables, unused_mut)]
-            let mut addendum = Heap::new();
-
-            let mut result =
-                vec![ atom_as_cell!($name, arity as u16),
-                      $(functor_term!( $dt($($value),*), arity, [], addendum ),)+ ];
-
-            result.extend(addendum.into_iter());
-            result
-        }
-    });
-    ($name:expr) => ({
-        vec![ atom_as_cell!($name) ]
-    });
-}
-
-macro_rules! functor_term {
-    (str(0), $arity:expr, $aux_lens:expr, $addendum:ident) => ({
-        str_loc_as_cell!($arity + 1)
-    });
-    (str($e:expr), $arity:expr, $aux_lens:expr, $addendum:ident) => ({
-        let len: usize = $aux_lens[0 .. $e].iter().sum();
-        str_loc_as_cell!($arity + 1 + len)
-    });
-    (str($h:expr, 0), $arity:expr, $aux_lens:expr, $addendum:ident) => ({
-        str_loc_as_cell!($arity + $h + 1)
-    });
-    (str($h:expr, $e:expr), $arity:expr, $aux_lens:expr, $addendum:ident) => ({
-        let len: usize = $aux_lens[0 .. $e].iter().sum();
-        str_loc_as_cell!($arity + $h + 1 + len)
-    });
-    (literal($e:expr), $arity:expr, $aux_lens:expr, $addendum:ident) => (
-        HeapCellValue::from($e)
-    );
-    (integer($e:expr, $arena:expr), $arity:expr, $aux_lens:expr, $addendum:ident) => (
-        HeapCellValue::arena_from(Number::arena_from($e, $arena), $arena)
-    );
-    (fixnum($e:expr), $arity:expr, $aux_lens:expr, $addendum:ident) => (
-        fixnum_as_cell!(Fixnum::build_with($e as i64))
-    );
-    (indexing_code_ptr($h:expr, $e:expr), $arity:expr, $aux_lens:expr, $addendum:ident) => ({
-        let stub =
-            match $e {
-                IndexingCodePtr::DynamicExternal(o) => functor!(atom!("dynamic_external"), [fixnum(o)]),
-                IndexingCodePtr::External(o) => functor!(atom!("external"), [fixnum(o)]),
-                IndexingCodePtr::Internal(o) => functor!(atom!("internal"), [fixnum(o)]),
-                IndexingCodePtr::Fail => {
-                    vec![atom_as_cell!(atom!("fail"))]
-                },
-            };
-
-        let len: usize = $aux_lens.iter().sum();
-        let h = len + $arity + 1 + $addendum.len() + $h;
-
-        $addendum.extend(stub.into_iter());
-
-        str_loc_as_cell!(h)
-    });
-    (number($arena:expr, $e:expr), $arity:expr, $aux_lens:expr, $addendum:ident) => (
-        HeapCellValue::from(($e, $arena))
-    );
-    (atom($e:expr), $arity:expr, $aux_lens:expr, $addendum:ident) => (
-        atom_as_cell!($e)
-    );
-    (string($h:expr, $e:expr), $arity:expr, $aux_lens:expr, $addendum: ident) => ({
-        let len: usize = $aux_lens.iter().sum();
-        let h = len + $arity + 1 + $addendum.len() + $h;
-
-        let cell = string_as_pstr_cell!($e);
-
-        $addendum.push(cell);
-        $addendum.push(empty_list_as_cell!());
-
-        heap_loc_as_cell!(h)
-    });
-    (boolean($e:expr), $arity:expr, $aux_lens:expr, $addendum: ident) => ({
-        if $e {
-            functor_term!(atom(atom!("true")), $arity, $aux_lens, $addendum)
-        } else {
-            functor_term!(atom(atom!("false")), $arity, $aux_lens, $addendum)
-        }
-    });
-    (cell($e:expr), $arity:expr, $aux_lens:expr, $addendum:ident) => (
-        $e
-    );
-}
-
 macro_rules! compare_number_instr {
     ($cmp: expr, $at_1: expr, $at_2: expr) => {{
         $cmp.set_terms($at_1, $at_2);
@@ -629,3 +446,44 @@ macro_rules! compare_term_test {
         $machine_st.compare_term_test($var_comparison)
     }};
 }
+
+macro_rules! step_or_resource_error {
+    ($machine_st:expr, $val:expr) => {{
+        match $val {
+            Ok(r) => r,
+            Err(err_loc) => {
+                $machine_st.throw_resource_error(err_loc);
+                return;
+            }
+        }
+    }};
+    ($machine_st:expr, $val:expr, $fail:block) => {{
+        match $val {
+            Ok(r) => r,
+            Err(err_loc) => {
+                $machine_st.throw_resource_error(err_loc);
+                $fail
+            }
+        }
+    }};
+}
+
+macro_rules! resource_error_call_result {
+    ($machine_st:expr, $val:expr) => {
+        step_or_resource_error!($machine_st, $val, {
+            return Err(vec![]);
+        })
+    };
+}
+
+macro_rules! heap_index {
+    ($idx:expr) => {
+        ($idx) * std::mem::size_of::<HeapCellValue>()
+    };
+}
+
+macro_rules! cell_index {
+    ($idx:expr) => {
+        (($idx) / std::mem::size_of::<HeapCellValue>())
+    };
+}

src/offset_table.rs

@@ -0,0 +1,422 @@
+use std::cell::UnsafeCell;
+use std::sync::Arc;
+use std::{fmt, mem, ptr};
+
+use arcu::atomic::Arcu;
+use arcu::epoch_counters::GlobalEpochCounterPool;
+use arcu::rcu_ref::RcuRef;
+use arcu::Rcu;
+use parking_lot::RwLock;
+
+use crate::machine::machine_indices::IndexPtr;
+use crate::raw_block::RawBlock;
+use crate::raw_block::RawBlockTraits;
+
+use ordered_float::OrderedFloat;
+
+const F64_TABLE_INIT_SIZE: usize = 1 << 16;
+const F64_TABLE_ALIGN: usize = 8;
+
+const CODE_INDEX_TABLE_INIT_SIZE: usize = 1 << 16;
+const CODE_INDEX_TABLE_ALIGN: usize = 8;
+
+impl RawBlockTraits for OrderedFloat<f64> {
+    #[inline]
+    fn init_size() -> usize {
+        F64_TABLE_INIT_SIZE
+    }
+
+    #[inline]
+    fn align() -> usize {
+        F64_TABLE_ALIGN
+    }
+}
+
+impl RawBlockTraits for IndexPtr {
+    #[inline]
+    fn init_size() -> usize {
+        CODE_INDEX_TABLE_INIT_SIZE
+    }
+
+    #[inline]
+    fn align() -> usize {
+        CODE_INDEX_TABLE_ALIGN
+    }
+}
+
+#[derive(Debug)]
+pub struct OffsetTableImpl<T: RawBlockTraits>(InnerOffsetTableImpl<T>);
+
+impl<T: RawBlockTraits> From<Arc<ConcurrentOffsetTable<T>>> for OffsetTableImpl<T> {
+    #[inline]
+    fn from(value: Arc<ConcurrentOffsetTable<T>>) -> Self {
+        OffsetTableImpl(InnerOffsetTableImpl::Concurrent(value))
+    }
+}
+
+impl<T: fmt::Debug + RawBlockTraits> OffsetTableImpl<T> {
+    #[inline(always)]
+    pub fn new() -> Self {
+        Self(InnerOffsetTableImpl::Serial(SerialOffsetTable::new()))
+    }
+
+    #[must_use = "the returned concurrent table must be absorbed into the owned OffsetTable"]
+    pub fn single_to_concurrent(&mut self) -> Arc<ConcurrentOffsetTable<T>> {
+        match &mut self.0 {
+            InnerOffsetTableImpl::Serial(serial_tbl) => {
+                let empty_serial_tbl = SerialOffsetTable {
+                    block: RawBlock::empty_block(),
+                };
+
+                let serial_tbl = mem::replace(serial_tbl, empty_serial_tbl);
+                let num_tbl_entries = serial_tbl.block.size() / size_of::<T>();
+                let block = Arcu::new(serial_tbl.block, GlobalEpochCounterPool);
+
+                let offset_locks: Vec<RwLock<()>> =
+                    (0..num_tbl_entries).map(|_| RwLock::new(())).collect();
+
+                let concurrent_tbl = Arc::new(ConcurrentOffsetTable {
+                    block,
+                    growth_lock: RwLock::new(()),
+                    offset_locks: RwLock::new(offset_locks),
+                });
+
+                self.0 = InnerOffsetTableImpl::Concurrent(concurrent_tbl.clone());
+
+                concurrent_tbl
+            }
+            InnerOffsetTableImpl::Concurrent(concurrent_tbl) => concurrent_tbl.clone(),
+        }
+    }
+
+    #[must_use = "the transition to a single-threaded offset table may fail if the concurrent table is held from multiple places"]
+    pub fn concurrent_to_single(&mut self) -> Result<(), ()> {
+        match &mut self.0 {
+            InnerOffsetTableImpl::Serial(_serial_tbl) => Ok(()),
+            InnerOffsetTableImpl::Concurrent(concurrent_tbl) => {
+                let table_arc = std::mem::replace(
+                    concurrent_tbl,
+                    Arc::new(ConcurrentOffsetTable {
+                        block: Arcu::new(RawBlock::empty_block(), GlobalEpochCounterPool),
+                        growth_lock: RwLock::new(()),
+                        offset_locks: RwLock::new(vec![]),
+                    }),
+                );
+
+                match Arc::try_unwrap(table_arc) {
+                    Ok(table) => {
+                        // this was the only instance of the concurrent table, as such
+                        // at this point no build_with/with_entry{_mut} call can be in-progress/made
+
+                        // this shouldn't be able to fail
+                        let raw_block =
+                            Arc::try_unwrap(table.block.replace(RawBlock::empty_block())).unwrap();
+                        self.0 =
+                            InnerOffsetTableImpl::Serial(SerialOffsetTable { block: raw_block });
+                        Ok(())
+                    }
+                    Err(table_arc) => {
+                        // restore the concurrent_tbl
+                        *concurrent_tbl = table_arc;
+                        Err(())
+                    }
+                }
+            }
+        }
+    }
+
+    #[inline]
+    pub fn get_entry(&self, offset: <Self as OffsetTable<T>>::Offset) -> T
+    where
+        Self: OffsetTable<T>,
+        T: Copy,
+    {
+        self.with_entry(offset, |value| *value)
+    }
+}
+
+impl<T: fmt::Debug + RawBlockTraits> Default for OffsetTableImpl<T> {
+    fn default() -> Self {
+        Self::new()
+    }
+}
+
+#[derive(Debug)]
+struct SerialOffsetTable<T: RawBlockTraits> {
+    block: RawBlock<T>,
+}
+
+#[derive(Debug)]
+pub struct ConcurrentOffsetTable<T: RawBlockTraits> {
+    block: Arcu<RawBlock<T>, GlobalEpochCounterPool>,
+    growth_lock: RwLock<()>,
+    offset_locks: RwLock<Vec<RwLock<()>>>,
+}
+
+#[derive(Debug)]
+enum InnerOffsetTableImpl<T: RawBlockTraits> {
+    Serial(SerialOffsetTable<T>),
+    #[allow(dead_code)]
+    Concurrent(Arc<ConcurrentOffsetTable<T>>),
+}
+
+impl<T: RawBlockTraits> InnerOffsetTableImpl<T> {
+    #[inline(always)]
+    fn build_with(&mut self, value: T) -> usize {
+        match self {
+            Self::Concurrent(concurrent_tbl) => concurrent_tbl.build_with(value),
+            Self::Serial(serial_tbl) => unsafe { serial_tbl.build_with(value) },
+        }
+    }
+
+    #[inline(always)]
+    fn with_entry<R, F: FnOnce(&T) -> R>(&self, offset: usize, f: F) -> R {
+        match self {
+            Self::Concurrent(concurrent_tbl) => concurrent_tbl.with_entry(offset, f),
+            Self::Serial(serial_tbl) => f(unsafe { serial_tbl.lookup(offset) }),
+        }
+    }
+
+    #[inline(always)]
+    fn with_entry_mut<R, F: FnOnce(&mut T) -> R>(&mut self, offset: usize, f: F) -> R {
+        match self {
+            Self::Concurrent(concurrent_tbl) => concurrent_tbl.with_entry_mut(offset, f),
+            Self::Serial(serial_tbl) => f(unsafe { serial_tbl.lookup_mut(offset) }),
+        }
+    }
+}
+
+pub trait OffsetTable<T: RawBlockTraits> {
+    type Offset: Copy + Into<usize>;
+
+    fn build_with(&mut self, value: T) -> Self::Offset;
+
+    fn with_entry<R, F: FnOnce(&T) -> R>(&self, offset: Self::Offset, f: F) -> R;
+    fn with_entry_mut<R, F: FnOnce(&mut T) -> R>(&mut self, offset: Self::Offset, f: F) -> R;
+}
+
+impl OffsetTable<OrderedFloat<f64>> for OffsetTableImpl<OrderedFloat<f64>> {
+    type Offset = F64Offset;
+
+    fn build_with(&mut self, value: OrderedFloat<f64>) -> F64Offset {
+        F64Offset(self.0.build_with(value))
+    }
+
+    #[inline]
+    fn with_entry<R, F: FnOnce(&OrderedFloat<f64>) -> R>(&self, offset: F64Offset, f: F) -> R {
+        self.0.with_entry(offset.into(), f)
+    }
+
+    #[inline]
+    fn with_entry_mut<R, F: FnOnce(&mut OrderedFloat<f64>) -> R>(
+        &mut self,
+        offset: F64Offset,
+        f: F,
+    ) -> R {
+        self.0.with_entry_mut(offset.into(), f)
+    }
+}
+
+impl OffsetTable<IndexPtr> for OffsetTableImpl<IndexPtr> {
+    type Offset = CodeIndexOffset;
+
+    fn build_with(&mut self, value: IndexPtr) -> CodeIndexOffset {
+        CodeIndexOffset(self.0.build_with(value))
+    }
+
+    #[inline]
+    fn with_entry<R, F: FnOnce(&IndexPtr) -> R>(&self, offset: CodeIndexOffset, f: F) -> R {
+        self.0.with_entry(offset.into(), f)
+    }
+
+    #[inline]
+    fn with_entry_mut<R, F: FnOnce(&mut IndexPtr) -> R>(
+        &mut self,
+        offset: CodeIndexOffset,
+        f: F,
+    ) -> R {
+        self.0.with_entry_mut(offset.into(), f)
+    }
+}
+
+impl<T: RawBlockTraits> SerialOffsetTable<T> {
+    #[inline]
+    fn new() -> Self {
+        Self {
+            block: RawBlock::new(),
+        }
+    }
+
+    unsafe fn build_with(&mut self, value: T) -> usize {
+        let mut ptr;
+
+        loop {
+            ptr = self.block.alloc(size_of::<T>());
+
+            if ptr.is_null() {
+                let new_block = self.block.grow_new().unwrap();
+                self.block = new_block;
+            } else {
+                break;
+            }
+        }
+
+        ptr::write(ptr as *mut T, value);
+        ptr.addr() - self.block.base.addr()
+    }
+
+    #[inline]
+    unsafe fn lookup(&self, offset: usize) -> &T {
+        &*self.block.base.add(offset).cast::<T>()
+    }
+
+    #[inline]
+    unsafe fn lookup_mut(&mut self, offset: usize) -> &mut T {
+        &mut *self.block.base.add(offset).cast::<T>().cast_mut()
+    }
+}
+
+impl<T: RawBlockTraits> ConcurrentOffsetTable<T> {
+    #[allow(clippy::missing_safety_doc)]
+    fn build_with(&self, value: T) -> usize {
+        let growth_lock = self.growth_lock.write();
+
+        // we don't have an index table for lookups as AtomTable does so
+        // just get the epoch after we take the upgrade lock
+        let mut block_epoch = self.block.read();
+        let mut ptr;
+
+        loop {
+            ptr = unsafe { block_epoch.alloc(mem::size_of::<T>()) };
+
+            if ptr.is_null() {
+                let new_block = unsafe { block_epoch.grow_new().unwrap() };
+                self.block.replace(new_block);
+                block_epoch = self.block.read();
+            } else {
+                break;
+            }
+        }
+
+        let new_tbl_sz = block_epoch.size() / size_of::<T>();
+        let mut offset_locks = self.offset_locks.write();
+
+        offset_locks.resize_with(new_tbl_sz, || RwLock::new(()));
+
+        unsafe {
+            ptr::write(ptr as *mut T, value);
+        }
+
+        let value = ptr.addr() - block_epoch.base.addr();
+
+        // AtomTable would have to update the index table at this point
+        // explicit drop to ensure we don't accidentally drop it early
+        drop(offset_locks);
+        drop(growth_lock);
+
+        value
+    }
+
+    fn with_entry<R, F: FnOnce(&T) -> R>(&self, offset: usize, f: F) -> R {
+        let outer_offset_lock = self.offset_locks.read();
+        let inner_offset_lock = outer_offset_lock[offset / size_of::<T>()].read();
+
+        let rcu_ref = RcuRef::try_map(self.block.read(), |raw_block| unsafe {
+            raw_block.base.add(offset).cast::<T>().as_ref()
+        })
+        .expect("offset valid");
+
+        let result = f(&*rcu_ref);
+
+        drop(inner_offset_lock);
+        drop(outer_offset_lock);
+
+        result
+    }
+
+    fn with_entry_mut<R, F: FnOnce(&mut T) -> R>(&self, offset: usize, f: F) -> R {
+        let growth_lock = self.growth_lock.read();
+        let outer_offset_lock = self.offset_locks.read();
+        let inner_offset_lock = outer_offset_lock[offset / size_of::<T>()].write();
+
+        let rcu_ref = RcuRef::try_map(self.block.read(), |raw_block| unsafe {
+            raw_block
+                .base
+                .add(offset)
+                .cast_mut()
+                .cast::<UnsafeCell<T>>()
+                .as_ref()
+        })
+        .expect("offset valid");
+
+        let result = f(unsafe { &mut *rcu_ref.get().as_mut().unwrap() });
+
+        drop(inner_offset_lock);
+        drop(outer_offset_lock);
+        drop(growth_lock);
+
+        result
+    }
+}
+
+pub type F64Table = OffsetTableImpl<OrderedFloat<f64>>;
+pub type CodeIndexTable = OffsetTableImpl<IndexPtr>;
+
+#[derive(Clone, Copy, Debug)]
+pub struct F64Offset(usize);
+
+impl From<usize> for F64Offset {
+    #[inline(always)]
+    fn from(offset: usize) -> Self {
+        Self(offset)
+    }
+}
+
+impl From<F64Offset> for usize {
+    fn from(val: F64Offset) -> Self {
+        val.0
+    }
+}
+
+#[derive(Debug, Clone, Copy)]
+pub struct CodeIndexOffset(usize);
+
+impl From<usize> for CodeIndexOffset {
+    #[inline(always)]
+    fn from(offset: usize) -> Self {
+        Self(offset)
+    }
+}
+
+impl From<CodeIndexOffset> for usize {
+    #[inline(always)]
+    fn from(val: CodeIndexOffset) -> Self {
+        val.0
+    }
+}
+
+impl CodeIndexOffset {
+    #[inline(always)]
+    pub fn to_u64(self) -> u64 {
+        self.0 as u64
+    }
+}
+
+impl fmt::Display for CodeIndexOffset {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        write!(f, "CodeIndexOffset({})", self.0)
+    }
+}
+
+impl F64Offset {
+    #[inline(always)]
+    pub fn to_u64(self) -> u64 {
+        self.0 as u64
+    }
+}
+
+impl fmt::Display for F64Offset {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        write!(f, "F64Offset({})", self.0)
+    }
+}

src/parser/ast.rs

@@ -2,21 +2,24 @@
 
 use crate::arena::*;
 use crate::atom_table::*;
-use crate::machine::machine_indices::*;
+use crate::offset_table::*;
 use crate::parser::char_reader::*;
 use crate::types::HeapCellValueTag;
 
 use std::cell::{Cell, Ref, RefCell, RefMut};
 use std::fmt;
-use std::hash::{Hash, Hasher};
+use std::hash::Hash;
+use std::hash::Hasher;
 use std::io::{Error as IOError, ErrorKind};
+use std::ops::Not;
+use std::ops::RangeInclusive;
 use std::ops::{Deref, Neg};
 use std::rc::Rc;
 use std::sync::Arc;
 use std::vec::Vec;
 
-use crate::parser::dashu::{Integer, Rational};
+use dashu::Integer;
-
+use dashu::Rational;
 use fxhash::FxBuildHasher;
 use indexmap::IndexMap;
 use scryer_modular_bitfield::error::OutOfBounds;
@@ -24,7 +27,7 @@ use scryer_modular_bitfield::prelude::*;
 
 pub type Specifier = u32;
 
-pub const MAX_ARITY: usize = 1023;
+pub const MAX_ARITY: usize = 255;
 
 #[allow(clippy::upper_case_acronyms)]
 #[derive(Debug, Clone, Copy, Eq, PartialEq)]
@@ -264,8 +267,8 @@ impl RegType {
 impl fmt::Display for RegType {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         match self {
-            RegType::Perm(val) => write!(f, "Y{}", val),
+            RegType::Perm(val) => write!(f, "Y{val}"),
-            RegType::Temp(val) => write!(f, "X{}", val),
+            RegType::Temp(val) => write!(f, "X{val}"),
         }
     }
 }
@@ -287,10 +290,10 @@ impl VarReg {
 impl fmt::Display for VarReg {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         match self {
-            VarReg::Norm(RegType::Perm(reg)) => write!(f, "Y{}", reg),
+            VarReg::Norm(RegType::Perm(reg)) => write!(f, "Y{reg}"),
-            VarReg::Norm(RegType::Temp(reg)) => write!(f, "X{}", reg),
+            VarReg::Norm(RegType::Temp(reg)) => write!(f, "X{reg}"),
-            VarReg::ArgAndNorm(RegType::Perm(reg), arg) => write!(f, "Y{} A{}", reg, arg),
+            VarReg::ArgAndNorm(RegType::Perm(reg), arg) => write!(f, "Y{reg} A{arg}"),
-            VarReg::ArgAndNorm(RegType::Temp(reg), arg) => write!(f, "X{} A{}", reg, arg),
+            VarReg::ArgAndNorm(RegType::Temp(reg), arg) => write!(f, "X{reg} A{arg}"),
         }
     }
 }
@@ -307,28 +310,6 @@ macro_rules! temp_v {
     };
 }
 
-#[derive(Debug, Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Hash)]
-pub enum GenContext {
-    Head,
-    Mid(usize),
-    Last(usize), // Mid & Last: chunk_num
-}
-
-impl GenContext {
-    #[inline]
-    pub fn chunk_num(self) -> usize {
-        match self {
-            GenContext::Head => 0,
-            GenContext::Mid(cn) | GenContext::Last(cn) => cn,
-        }
-    }
-
-    #[inline]
-    pub fn is_last(self) -> bool {
-        matches!(self, GenContext::Last(_))
-    }
-}
-
 #[bitfield]
 #[derive(Copy, Clone, Debug, PartialEq, Eq, Ord, PartialOrd, Hash)]
 pub struct OpDesc {
@@ -420,7 +401,7 @@ pub fn default_op_dir() -> OpDir {
     op_dir
 }
 
-#[derive(Debug, Clone)]
+#[derive(Debug, Copy, Clone)]
 pub enum ArithmeticError {
     NonEvaluableFunctor(Literal, usize),
     UninstantiatedVar,
@@ -465,9 +446,9 @@ impl ParserError {
             ParserError::InvalidSingleQuotedCharacter(..) => {
                 atom!("invalid_single_quoted_character")
             }
-	    ParserError::InfiniteFloat(..) => {
+            ParserError::InfiniteFloat(..) => {
-		atom!("infinite_float")
+                atom!("infinite_float")
-	    }
+            }
             ParserError::IO(e) if e.kind() == ErrorKind::UnexpectedEof => {
                 atom!("unexpected_end_of_file")
             }
@@ -570,9 +551,90 @@ pub struct Fixnum {
     tag: B6,
 }
 
+mod private {
+    use dashu::Integer;
+
+    pub(crate) trait FitsInFixnumSeal {}
+    pub(crate) trait MightNotFitInFixnumSeal {}
+
+    macro_rules! impl_fits_in_fixnum {
+        ($t:ty) => {
+            impl $crate::parser::ast::private::FitsInFixnumSeal for $t {}
+
+            impl $crate::parser::ast::FitsInFixnum for $t {
+                fn into_i56(self) -> i64 {
+                    self.into()
+                }
+            }
+        };
+    }
+
+    impl_fits_in_fixnum!(u8);
+    impl_fits_in_fixnum!(i8);
+    impl_fits_in_fixnum!(u16);
+    impl_fits_in_fixnum!(i16);
+    impl_fits_in_fixnum!(u32);
+    impl_fits_in_fixnum!(i32);
+
+    impl FitsInFixnumSeal for char {}
+    impl super::FitsInFixnum for char {
+        fn into_i56(self) -> i64 {
+            u32::from(self) as i64
+        }
+    }
+
+    impl MightNotFitInFixnumSeal for i64 {}
+    impl MightNotFitInFixnumSeal for &Integer {}
+    impl MightNotFitInFixnumSeal for Integer {}
+    impl MightNotFitInFixnumSeal for usize {}
+}
+
+#[allow(private_bounds)]
+pub trait FitsInFixnum: private::FitsInFixnumSeal {
+    fn into_i56(self) -> i64;
+}
+
+#[allow(private_bounds)]
+pub trait MightNotFitInFixnum: private::MightNotFitInFixnumSeal {
+    fn try_into_i56(self) -> Option<i64>;
+}
+
+impl<T> MightNotFitInFixnum for T
+where
+    T: private::MightNotFitInFixnumSeal + TryInto<i64>,
+{
+    fn try_into_i56(self) -> Option<i64> {
+        let val = self.try_into().ok()?;
+        if Fixnum::RANGE.contains(&val) {
+            Some(val)
+        } else {
+            None
+        }
+    }
+}
+
 impl Fixnum {
+    pub(crate) const MIN: i64 = -(1 << 55);
+    pub(crate) const MAX: i64 = (1 << 55) - 1;
+    const RANGE: RangeInclusive<i64> = Self::MIN..=Self::MAX;
+
+    // if you have a type that is not guaranteed to fit use `Fixnum::build_with_checked` or `Fixnum::build_with_unchecked` instead
     #[inline]
-    pub fn build_with(num: i64) -> Self {
+    pub fn build_with(num: impl FitsInFixnum) -> Self {
+        // Safety: FitsInFixnum is only implemented by types that only have valid values
+        // and FitsInFixnumSeal ensures no one outside this crate can violate that
+        unsafe { Self::build_with_unchecked(num.into_i56()) }
+    }
+
+    #[inline]
+    pub unsafe fn build_with_unchecked(num: i64) -> Self {
+        debug_assert!(
+            Self::RANGE.contains(&num),
+            "{num} should be in the range {}..={}",
+            Self::MIN,
+            Self::MAX
+        );
+
         Fixnum::new()
             .with_num(u64::from_ne_bytes(num.to_ne_bytes()) & ((1 << 56) - 1))
             .with_tag(HeapCellValueTag::Fixnum as u8)
@@ -581,12 +643,8 @@ impl Fixnum {
     }
 
     #[inline]
-    pub fn as_cutpoint(num: i64) -> Self {
+    pub fn as_cutpoint(self) -> Self {
-        Fixnum::new()
+        self.with_tag(HeapCellValueTag::CutPoint as u8)
-            .with_num(u64::from_ne_bytes(num.to_ne_bytes()) & ((1 << 56) - 1))
-            .with_tag(HeapCellValueTag::CutPoint as u8)
-            .with_m(false)
-            .with_f(false)
     }
 
     #[inline]
@@ -595,20 +653,14 @@ impl Fixnum {
         HeapCellValueTag::from_bytes(self.tag()).unwrap()
     }
 
+    // if you have a type that is guaranteed to fit use `Fixnum::build_with` instead
     #[inline]
-    pub fn build_with_checked(num: i64) -> Result<Self, OutOfBounds> {
+    pub fn build_with_checked(num: impl MightNotFitInFixnum) -> Result<Self, OutOfBounds> {
-        const UPPER_BOUND: i64 = (1 << 55) - 1;
+        Ok(unsafe {
-        const LOWER_BOUND: i64 = -(1 << 55);
+            // Safety: all MightNotFitInFixnum impls return None when the value is out-of-bounds
-
+            // and MightNotFitInFixnumSeal ensures no one outside this crate can violate that
-        if (LOWER_BOUND..=UPPER_BOUND).contains(&num) {
+            Self::build_with_unchecked(num.try_into_i56().ok_or(OutOfBounds {})?)
-            Ok(Fixnum::new()
+        })
-                .with_m(false)
-                .with_f(false)
-                .with_tag(HeapCellValueTag::Fixnum as u8)
-                .with_num(u64::from_ne_bytes(num.to_ne_bytes()) & ((1 << 56) - 1)))
-        } else {
-            Err(OutOfBounds {})
-        }
     }
 
     #[inline]
@@ -618,6 +670,10 @@ impl Fixnum {
         debug_assert!(!overflowed);
         n
     }
+
+    pub fn checked_abs(self) -> Option<Self> {
+        Self::build_with_checked(self.get_num().abs()).ok()
+    }
 }
 
 impl Neg for Fixnum {
@@ -625,23 +681,33 @@ impl Neg for Fixnum {
 
     #[inline]
     fn neg(self) -> Self::Output {
-        Fixnum::build_with(-self.get_num())
+        // Safety: the truncating behaviour is correct
+        unsafe { Self::build_with_unchecked(-self.get_num()) }
     }
 }
 
-#[derive(Debug, Copy, Clone, PartialEq, Eq, Hash)]
+impl Not for Fixnum {
+    type Output = Self;
+
+    #[inline]
+    fn not(self) -> Self::Output {
+        // Safety: the truncating behaviour is correct
+        unsafe { Self::build_with_unchecked(!self.get_num()) }
+    }
+}
+
+#[derive(Debug, Copy, Clone)]
 pub enum Literal {
     Atom(Atom),
-    Char(char),
+    CodeIndexOffset(CodeIndexOffset),
-    CodeIndex(CodeIndex),
     Fixnum(Fixnum),
     Integer(TypedArenaPtr<Integer>),
     Rational(TypedArenaPtr<Rational>),
-    Float(F64Offset),
+    F64Offset(F64Offset),
-    String(Atom),
 }
 
-impl From<F64Ptr> for Literal {
+/*
+impl From<F64Ptr<'_>> for Literal {
     #[inline(always)]
     fn from(ptr: F64Ptr) -> Literal {
         Literal::Float(ptr.as_offset())
@@ -654,16 +720,15 @@ impl fmt::Display for Literal {
             Literal::Atom(ref atom) => {
                 write!(f, "{}", atom.flat_index())
             }
-            Literal::Char(c) => write!(f, "'{}'", *c as u32),
+            Literal::CodeIndexOffset(i) => write!(f, "{}", *i),
-            Literal::CodeIndex(i) => write!(f, "{:x}", i.as_ptr() as u64),
             Literal::Fixnum(n) => write!(f, "{}", n.get_num()),
             Literal::Integer(ref n) => write!(f, "{}", n),
             Literal::Rational(ref n) => write!(f, "{}", n),
-            Literal::Float(ref n) => write!(f, "{}", *n),
+            Literal::FloatOffset(ref n) => write!(f, "{}", *n),
-            Literal::String(ref s) => write!(f, "\"{}\"", s.as_str()),
         }
     }
 }
+*/
 
 impl Literal {
     pub fn as_atom(&self, atom_tbl: &Arc<AtomTable>) -> Option<Atom> {
@@ -742,20 +807,20 @@ impl From<&str> for VarPtr {
 pub enum Var {
     Generated(usize),
     InSitu(usize),
-    Named(String),
+    Named(Rc<String>),
 }
 
 impl From<String> for Var {
     #[inline(always)]
     fn from(value: String) -> Var {
-        Var::Named(value)
+        Var::Named(Rc::new(value))
     }
 }
 
 impl From<&str> for Var {
     #[inline(always)]
     fn from(value: &str) -> Var {
-        Var::Named(value.to_owned())
+        Var::Named(Rc::new(value.to_owned()))
     }
 }
 
@@ -764,8 +829,8 @@ impl Var {
     #[inline(always)]
     pub fn to_string(&self) -> String {
         match self {
-            Var::InSitu(n) | Var::Generated(n) => format!("_{}", n),
+            Var::InSitu(n) | Var::Generated(n) => format!("_{n}"),
-            Var::Named(value) => value.to_owned(),
+            Var::Named(value) => value.as_ref().clone(),
         }
     }
 }
@@ -778,8 +843,8 @@ pub enum Term {
     Literal(Cell<RegType>, Literal),
     // PartialString wraps a String in anticipation of it absorbing
     // other PartialString variants in as_partial_string.
-    PartialString(Cell<RegType>, String, Box<Term>),
+    PartialString(Cell<RegType>, Rc<String>, Box<Term>),
-    CompleteString(Cell<RegType>, Atom),
+    CompleteString(Cell<RegType>, Rc<String>),
     Var(Cell<VarReg>, VarPtr),
 }
 
@@ -792,10 +857,9 @@ impl Term {
     }
 
     pub fn name(&self) -> Option<Atom> {
-        match self {
+        match *self {
-            &Term::Literal(_, Literal::Atom(ref atom)) | &Term::Clause(_, ref atom, ..) => {
+            Term::Literal(_, Literal::Atom(atom)) => Some(atom),
-                Some(*atom)
+            Term::Clause(_, atom, ..) => Some(atom),
-            }
             _ => None,
         }
     }
@@ -810,7 +874,7 @@ impl Term {
 
 pub(crate) fn unfold_by_str_once(term: &mut Term, s: Atom) -> Option<(Term, Term)> {
     if let Term::Clause(_, ref name, ref mut subterms) = term {
-        if let Some(Term::Literal(_, Literal::CodeIndex(_))) = subterms.last() {
+        if let Some(Term::Literal(_, Literal::CodeIndexOffset(_))) = subterms.last() {
             subterms.pop();
         }
 

src/parser/lexer.rs

@@ -1,11 +1,13 @@
-use crate::arena::F64Ptr;
+use crate::arena::*;
-use crate::arena::TypedArenaPtr;
 use crate::atom_table::*;
 pub use crate::machine::machine_state::*;
+use crate::offset_table::*;
 use crate::parser::ast::*;
 use crate::parser::char_reader::*;
 use crate::parser::dashu::Integer;
 
+use ordered_float::OrderedFloat;
+
 use std::convert::TryFrom;
 use std::fmt;
 
@@ -28,10 +30,11 @@ struct LayoutInfo {
     more: bool,
 }
 
-#[derive(Debug, PartialEq)]
+#[derive(Debug)]
 pub enum Token {
     Literal(Literal),
     Var(String),
+    String(String),
     Open,              // '('
     OpenCT,            // '('
     Close,             // ')'
@@ -55,16 +58,17 @@ impl Token {
 enum Number {
     BigInt(TypedArenaPtr<Integer>),
     Fixnum(Fixnum),
-    Float(F64Ptr),
+    Float(F64Offset),
 }
 
 impl Number {
     #[inline]
+    #[allow(clippy::wrong_self_convention)]
     fn to_literal(self) -> Literal {
         match self {
             Number::BigInt(ibig) => Literal::Integer(ibig),
             Number::Fixnum(fixnum) => Literal::Fixnum(fixnum),
-            Number::Float(f) => Literal::Float(f.as_offset()),
+            Number::Float(f) => Literal::F64Offset(f),
         }
     }
 }
@@ -77,6 +81,7 @@ enum NumberToken {
 
 impl NumberToken {
     #[inline]
+    #[allow(clippy::wrong_self_convention)]
     fn to_token(self) -> Option<Token> {
         match self {
             NumberToken::Number(number) => Some(Token::Literal(number.to_literal())),
@@ -100,7 +105,7 @@ macro_rules! try_nt {
     }};
 }
 
-pub struct Lexer<'a, R> {
+pub(crate) struct Lexer<'a, R> {
     pub(crate) reader: R,
     pub(crate) machine_st: &'a mut MachineState,
     pub(crate) line_num: usize,
@@ -109,7 +114,7 @@ pub struct Lexer<'a, R> {
 
 impl<'a, R: fmt::Debug> fmt::Debug for Lexer<'a, R> {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        f.debug_struct("Lexer")
+        f.debug_struct("LexerParser")
             .field("reader", &"&'a mut R") // Hacky solution.
             .field("line_num", &self.line_num)
             .field("col_num", &self.col_num)
@@ -119,7 +124,7 @@ impl<'a, R: fmt::Debug> fmt::Debug for Lexer<'a, R> {
 
 impl<'a, R: CharRead> Lexer<'a, R> {
     pub fn new(src: R, machine_st: &'a mut MachineState) -> Self {
-        Lexer {
+        Self {
             reader: src,
             machine_st,
             line_num: 0,
@@ -505,7 +510,13 @@ impl<'a, R: CharRead> Lexer<'a, R> {
                 if hexadecimal_digit_char!(c) {
                     self.skip_char(c);
                     token.push(c);
-                    c = try_nt!(token, self.lookahead_char());
+                    c = match self.lookahead_char() {
+                        Ok(c) => c,
+                        Err(e) if e.is_unexpected_eof() => {
+                            break;
+                        }
+                        Err(e) => return Err(e),
+                    };
                 } else {
                     break;
                 }
@@ -530,7 +541,13 @@ impl<'a, R: CharRead> Lexer<'a, R> {
                 if octal_digit_char!(c) {
                     self.skip_char(c);
                     token.push(c);
-                    c = try_nt!(token, self.lookahead_char());
+                    c = match self.lookahead_char() {
+                        Ok(c) => c,
+                        Err(e) if e.is_unexpected_eof() => {
+                            break;
+                        }
+                        Err(e) => return Err(e),
+                    };
                 } else {
                     break;
                 }
@@ -555,7 +572,13 @@ impl<'a, R: CharRead> Lexer<'a, R> {
                 if binary_digit_char!(c) {
                     self.skip_char(c);
                     token.push(c);
-                    c = try_nt!(token, self.lookahead_char());
+                    c = match self.lookahead_char() {
+                        Ok(c) => c,
+                        Err(e) if e.is_unexpected_eof() => {
+                            break;
+                        }
+                        Err(e) => return Err(e),
+                    };
                 } else {
                     break;
                 }
@@ -632,7 +655,9 @@ impl<'a, R: CharRead> Lexer<'a, R> {
 
                 if !token.is_empty() && token.chars().nth(1).is_none() {
                     if let Some(c) = token.chars().next() {
-                        return Ok(Token::Literal(Literal::Char(c)));
+                        return Ok(Token::Literal(Literal::Atom(
+                            AtomCell::new_char_inlined(c).get_name(),
+                        )));
                     }
                 }
             } else {
@@ -679,12 +704,8 @@ impl<'a, R: CharRead> Lexer<'a, R> {
         }
     }
 
-    fn parse_integer_by_radix(
+    fn parse_integer_by_radix(&mut self, token: &str, radix: u32) -> Result<Number, ParserError> {
-        &mut self,
+        i64::from_str_radix(token, radix)
-        token: &String,
-        radix: u32,
-    ) -> Result<Number, ParserError> {
-        i64::from_str_radix(&token, radix)
             .map(|n| {
                 Fixnum::build_with_checked(n)
                     .map(Number::Fixnum)
@@ -701,7 +722,7 @@ impl<'a, R: CharRead> Lexer<'a, R> {
     }
 
     #[inline]
-    fn parse_integer(&mut self, token: &String) -> Result<Number, ParserError> {
+    fn parse_integer(&mut self, token: &str) -> Result<Number, ParserError> {
         self.parse_integer_by_radix(token, 10)
     }
 
@@ -785,6 +806,7 @@ impl<'a, R: CharRead> Lexer<'a, R> {
                         }
 
                         let n = parse_float_lossy(&token)?;
+
                         Ok(NumberToken::Number(Number::Float(float_alloc!(
                             n,
                             self.machine_st.arena
@@ -847,7 +869,7 @@ impl<'a, R: CharRead> Lexer<'a, R> {
                 }
 
                 self.get_single_quoted_char()
-                    .map(|c| NumberToken::Number(Number::Fixnum(Fixnum::build_with(c as i64))))
+                    .map(|c| NumberToken::Number(Number::Fixnum(Fixnum::build_with(c))))
                     .or_else(|err| {
                         match err {
                             ParserError::UnexpectedChar('\'', ..) => {}
@@ -933,13 +955,14 @@ impl<'a, R: CharRead> Lexer<'a, R> {
                 Ok(n) => Ok(Token::Literal(n.to_literal())),
                 Err(_) => {
                     let n = parse_float_lossy(&token_string)?;
-                    Ok(Token::Literal(Literal::Float(
+                    Ok(Token::Literal(Literal::F64Offset(float_alloc!(
-                        float_alloc!(n, self.machine_st.arena).as_offset(),
+                        n,
-                    )))
+                        self.machine_st.arena
+                    ))))
                 }
             },
-            Ok(NumberToken::Number(n)) => return Ok(Token::Literal(n.to_literal())),
+            Ok(NumberToken::Number(n)) => Ok(Token::Literal(n.to_literal())),
-            Err(e) => return Err(e),
+            Err(e) => Err(e),
         }
     }
 
@@ -1028,12 +1051,12 @@ impl<'a, R: CharRead> Lexer<'a, R> {
 
                 if c == '"' {
                     let s = self.char_code_list_token(c)?;
-                    let atom = AtomTable::build_with(&self.machine_st.atom_tbl, &s);
 
                     return if let DoubleQuotes::Atom = self.machine_st.flags.double_quotes {
+                        let atom = AtomTable::build_with(&self.machine_st.atom_tbl, &s);
                         Ok(Token::Literal(Literal::Atom(atom)))
                     } else {
-                        Ok(Token::Literal(Literal::String(atom)))
+                        Ok(Token::String(s))
                     };
                 }
 

src/parser/parser.rs

@@ -3,6 +3,7 @@ use dashu::Rational;
 
 use crate::arena::*;
 use crate::atom_table::*;
+use crate::offset_table::OffsetTable;
 use crate::parser::ast::*;
 use crate::parser::char_reader::*;
 use crate::parser::lexer::*;
@@ -10,6 +11,7 @@ use crate::parser::lexer::*;
 use std::cell::Cell;
 use std::mem;
 use std::ops::Neg;
+use std::rc::Rc;
 
 #[derive(Debug, Clone, Copy, PartialEq)]
 enum TokenType {
@@ -73,7 +75,6 @@ pub(crate) fn as_partial_string(
                 return Err(Term::Cons(Cell::default(), Box::new(head), Box::new(tail)));
             }
         }
-        Term::Literal(_, Literal::Char(c)) => c.to_string(),
         _ => {
             return Err(Term::Cons(Cell::default(), Box::new(head), Box::new(tail)));
         }
@@ -93,9 +94,6 @@ pub(crate) fn as_partial_string(
                             return Err(Term::Cons(Cell::default(), Box::new(head), orig_tail));
                         }
                     }
-                    Term::Literal(_, Literal::Char(c)) => {
-                        string.push(*c);
-                    }
                     _ => {
                         tail = Term::Cons(
                             Cell::default(),
@@ -113,7 +111,7 @@ pub(crate) fn as_partial_string(
                 tail_ref = tail;
             }
             Term::CompleteString(_, cstr) => {
-                string += &*cstr.as_str();
+                string += cstr.as_str();
                 tail = Term::Literal(Cell::default(), Literal::Atom(atom!("[]")));
                 break;
             }
@@ -124,13 +122,17 @@ pub(crate) fn as_partial_string(
         }
     }
 
-    match &tail {
+    match tail {
         Term::AnonVar | Term::Var(..) => Ok((string, Some(Box::new(tail)))),
         Term::Literal(_, Literal::Atom(atom!("[]"))) => Ok((string, None)),
-        Term::Literal(_, Literal::String(tail)) => {
+        Term::CompleteString(_, tail) => {
-            string += &*tail.as_str();
+            string += &tail;
             Ok((string, None))
         }
+        Term::PartialString(_, tail_string, tail) => {
+            string += &tail_string;
+            Ok((string, Some(tail)))
+        }
         _ => Ok((string, Some(Box::new(tail)))),
     }
 }
@@ -237,7 +239,7 @@ pub struct Parser<'a, R> {
     terms: Vec<Term>,
 }
 
-fn read_tokens<R: CharRead>(lexer: &mut Lexer<R>) -> Result<Vec<Token>, ParserError> {
+pub fn read_tokens<R: CharRead>(lexer: &mut Lexer<'_, R>) -> Result<Vec<Token>, ParserError> {
     let mut tokens = vec![];
 
     loop {
@@ -263,22 +265,30 @@ fn read_tokens<R: CharRead>(lexer: &mut Lexer<R>) -> Result<Vec<Token>, ParserEr
     }
 
     tokens.reverse();
-
     Ok(tokens)
 }
 
-fn atomize_term(atom_tbl: &AtomTable, term: &Term) -> Option<Atom> {
+fn atomize_term(term: &Term) -> Option<Atom> {
     match term {
-        Term::Literal(_, ref c) => atomize_constant(atom_tbl, *c),
+        &Term::Literal(_, Literal::Atom(c)) => Some(c),
         _ => None,
     }
 }
 
-fn atomize_constant(atom_tbl: &AtomTable, c: Literal) -> Option<Atom> {
+impl TokenType {
-    match c {
+    fn sep_to_atom(&mut self) -> Option<Atom> {
-        Literal::Atom(ref name) => Some(*name),
+        match self {
-        Literal::Char(c) => Some(AtomTable::build_with(atom_tbl, &c.to_string())),
+            TokenType::Open | TokenType::OpenCT => Some(atom!("(")),
-        _ => None,
+            TokenType::Close => Some(atom!(")")),
+            TokenType::OpenList => Some(atom!("[")),
+            TokenType::CloseList => Some(atom!("]")),
+            TokenType::OpenCurly => Some(atom!("{")),
+            TokenType::CloseCurly => Some(atom!("}")),
+            TokenType::HeadTailSeparator => Some(atom!("|")),
+            TokenType::Comma => Some(atom!(",")),
+            TokenType::End => Some(atom!(".")),
+            _ => None,
+        }
     }
 }
 
@@ -301,21 +311,6 @@ impl<'a, R: CharRead> Parser<'a, R> {
         }
     }
 
-    fn sep_to_atom(&mut self, tt: TokenType) -> Option<Atom> {
-        match tt {
-            TokenType::Open | TokenType::OpenCT => Some(atom!("(")),
-            TokenType::Close => Some(atom!(")")),
-            TokenType::OpenList => Some(atom!("[")),
-            TokenType::CloseList => Some(atom!("]")),
-            TokenType::OpenCurly => Some(atom!("{")),
-            TokenType::CloseCurly => Some(atom!("}")),
-            TokenType::HeadTailSeparator => Some(atom!("|")),
-            TokenType::Comma => Some(atom!(",")),
-            TokenType::End => Some(atom!(".")),
-            _ => None,
-        }
-    }
-
     fn get_term_name(&mut self, td: TokenDesc) -> Option<Atom> {
         match td.tt {
             TokenType::HeadTailSeparator => Some(atom!("|")),
@@ -385,9 +380,7 @@ impl<'a, R: CharRead> Parser<'a, R> {
 
     fn shift(&mut self, token: Token, priority: usize, spec: Specifier) {
         let tt = match token {
-            Token::Literal(Literal::String(s))
+            Token::String(s) if self.lexer.machine_st.flags.double_quotes.is_codes() => {
-                if self.lexer.machine_st.flags.double_quotes.is_codes() =>
-            {
                 let mut list = Term::Literal(Cell::default(), Literal::Atom(atom!("[]")));
 
                 for c in s.as_str().chars().rev() {
@@ -395,7 +388,7 @@ impl<'a, R: CharRead> Parser<'a, R> {
                         Cell::default(),
                         Box::new(Term::Literal(
                             Cell::default(),
-                            Literal::Fixnum(Fixnum::build_with(c as i64)),
+                            Literal::Fixnum(Fixnum::build_with(c)),
                         )),
                         Box::new(list),
                     );
@@ -404,10 +397,10 @@ impl<'a, R: CharRead> Parser<'a, R> {
                 self.terms.push(list);
                 TokenType::Term
             }
-            Token::Literal(Literal::String(s))
+            Token::String(s) => {
-                if self.lexer.machine_st.flags.double_quotes.is_chars() =>
+                debug_assert!(self.lexer.machine_st.flags.double_quotes.is_chars());
-            {
+                self.terms
-                self.terms.push(Term::CompleteString(Cell::default(), s));
+                    .push(Term::CompleteString(Cell::default(), Rc::new(s)));
                 TokenType::Term
             }
             Token::Literal(c) => {
@@ -549,17 +542,13 @@ impl<'a, R: CharRead> Parser<'a, R> {
         let idx = self.terms.len() - arity;
 
         if TokenType::Term == self.stack[stack_len].tt
-            && atomize_term(&self.lexer.machine_st.atom_tbl, &self.terms[idx - 1]).is_some()
+            && atomize_term(&self.terms[idx - 1]).is_some()
         {
             self.stack.truncate(stack_len + 1);
 
             let mut subterms: Vec<_> = self.terms.drain(idx..).collect();
 
-            if let Some(name) = self
+            if let Some(name) = self.terms.pop().and_then(|t| atomize_term(&t)) {
-                .terms
-                .pop()
-                .and_then(|t| atomize_term(&self.lexer.machine_st.atom_tbl, &t))
-            {
                 // reduce the '.' functor to a cons cell if it applies.
                 if name == atom!(".") && subterms.len() == 2 {
                     let tail = subterms.pop().unwrap();
@@ -567,12 +556,10 @@ impl<'a, R: CharRead> Parser<'a, R> {
 
                     self.terms.push(match as_partial_string(head, tail) {
                         Ok((string_buf, Some(tail))) => {
-                            Term::PartialString(Cell::default(), string_buf, tail)
+                            Term::PartialString(Cell::default(), Rc::new(string_buf), tail)
                         }
                         Ok((string_buf, None)) => {
-                            let atom =
+                            Term::CompleteString(Cell::default(), Rc::new(string_buf))
-                                AtomTable::build_with(&self.lexer.machine_st.atom_tbl, &string_buf);
-                            Term::CompleteString(Cell::default(), atom)
                         }
                         Err(term) => term,
                     });
@@ -754,11 +741,10 @@ impl<'a, R: CharRead> Parser<'a, R> {
         self.terms.push(match list {
             Term::Cons(_, head, tail) => match as_partial_string(*head, *tail) {
                 Ok((string_buf, Some(tail))) => {
-                    Term::PartialString(Cell::default(), string_buf, tail)
+                    Term::PartialString(Cell::default(), Rc::new(string_buf), tail)
                 }
                 Ok((string_buf, None)) => {
-                    let atom = AtomTable::build_with(&self.lexer.machine_st.atom_tbl, &string_buf);
+                    Term::CompleteString(Cell::default(), Rc::new(string_buf))
-                    Term::CompleteString(Cell::default(), atom)
                 }
                 Err(term) => term,
             },
@@ -846,7 +832,7 @@ impl<'a, R: CharRead> Parser<'a, R> {
                     return false;
                 }
 
-                if let Some(atom) = self.sep_to_atom(self.stack[idx].tt) {
+                if let Some(atom) = self.stack[idx].tt.sep_to_atom() {
                     self.terms
                         .push(Term::Literal(Cell::default(), Literal::Atom(atom)));
                 }
@@ -967,8 +953,8 @@ impl<'a, R: CharRead> Parser<'a, R> {
         }
 
         match token {
-            Token::Literal(Literal::Fixnum(n)) => {
+            Token::String(string) => {
-                self.negate_number(n, |n, _| -n, |n, _| Literal::Fixnum(n))
+                self.shift(Token::String(string), 0, TERM);
             }
             Token::Literal(Literal::Integer(n)) => {
                 self.negate_number(n, negate_int_rc, |n, _| Literal::Integer(n))
@@ -976,21 +962,34 @@ impl<'a, R: CharRead> Parser<'a, R> {
             Token::Literal(Literal::Rational(n)) => {
                 self.negate_number(n, negate_rat_rc, |r, _| Literal::Rational(r))
             }
-            Token::Literal(Literal::Float(n)) if F64Ptr::from_offset(n).is_infinite() => {
+            Token::Literal(Literal::F64Offset(n))
-		return Err(ParserError::InfiniteFloat(
+                if self
-		    self.lexer.line_num,
+                    .lexer
-		    self.lexer.col_num,
+                    .machine_st
-		));
+                    .arena
-	    }
+                    .f64_tbl
-	    Token::Literal(Literal::Float(n)) => self.negate_number(
+                    .get_entry(n)
-                **n.as_ptr(),
+                    .is_infinite() =>
-                |n, _| -n,
+            {
-                |n, arena| Literal::from(float_alloc!(n, arena)),
+                return Err(ParserError::InfiniteFloat(
-	    ),
+                    self.lexer.line_num,
-            Token::Literal(c) => {
+                    self.lexer.col_num,
-                let atomized = atomize_constant(&self.lexer.machine_st.atom_tbl, c);
+                ));
+            }
+            Token::Literal(Literal::F64Offset(n)) => {
+                let n = self.lexer.machine_st.arena.f64_tbl.get_entry(n);
 
-                if let Some(name) = atomized {
+                self.negate_number(
+                    n,
+                    |n, _| -n,
+                    |n, arena| Literal::F64Offset(arena.f64_tbl.build_with(n)),
+                )
+            }
+            Token::Literal(Literal::Fixnum(n)) => {
+                self.negate_number(n, |n, _| -n, |n, _| Literal::Fixnum(n))
+            }
+            Token::Literal(c) => {
+                if let Literal::Atom(name) = c {
                     if !self.shift_op(name, op_dir)? {
                         self.shift(Token::Literal(c), 0, TERM);
                     }

src/raw_block.rs

@@ -19,7 +19,7 @@ pub struct RawBlock<T: RawBlockTraits> {
 
 impl<T: RawBlockTraits> RawBlock<T> {
     #[inline]
-    fn empty_block() -> Self {
+    pub fn empty_block() -> Self {
         RawBlock {
             base: ptr::null(),
             top: ptr::null(),
@@ -66,8 +66,8 @@ impl<T: RawBlockTraits> RawBlock<T> {
                 false
             } else {
                 self.base = new_base;
-                self.top = (self.base as usize + size * 2) as *const _;
+                self.top = self.base.add(size * 2);
-                *self.ptr.get_mut() = (self.base as usize + size) as *mut _;
+                *self.ptr.get_mut() = self.base.add(size).cast_mut();
                 true
             }
         }
@@ -83,7 +83,7 @@ impl<T: RawBlockTraits> RawBlock<T> {
                 // allocation failed
                 None
             } else {
-                let allocated = (*self.ptr.get()) as usize - self.base as usize;
+                let allocated = (*self.ptr.get()).addr() - self.base.addr();
                 self.base.copy_to(new_block.base.cast_mut(), allocated);
                 *new_block.ptr.get_mut() = new_block.base.add(allocated).cast_mut();
                 Some(new_block)
@@ -93,7 +93,7 @@ impl<T: RawBlockTraits> RawBlock<T> {
 
     #[inline]
     pub fn size(&self) -> usize {
-        self.top as usize - self.base as usize
+        self.top.addr() - self.base.addr()
     }
 
     #[inline(always)]
@@ -105,7 +105,7 @@ impl<T: RawBlockTraits> RawBlock<T> {
             self.base
         );
 
-        self.top as usize - (*self.ptr.get()) as usize
+        self.top.addr() - (*self.ptr.get()).addr()
     }
 
     pub unsafe fn alloc(&self, size: usize) -> *mut u8 {

src/read.rs

@@ -1,4 +1,5 @@
 use crate::parser::ast::*;
+use crate::parser::lexer::Lexer;
 use crate::parser::parser::*;
 
 use crate::atom_table::*;
@@ -32,9 +33,9 @@ use std::sync::Arc;
 type SubtermDeque = VecDeque<(usize, usize)>;
 
 pub(crate) fn devour_whitespace<R: CharRead>(
-    parser: &mut Parser<'_, R>,
+    lexer: &mut Lexer<'_, R>,
 ) -> Result<bool, ParserError> {
-    match parser.lexer.scan_for_layout() {
+    match lexer.scan_for_layout() {
         Err(e) if e.is_unexpected_eof() => Ok(true),
         Err(e) => Err(e),
         Ok(_) => Ok(false),
@@ -80,7 +81,7 @@ impl MachineState {
         };
 
         inner.add_lines_read(num_lines_read);
-        write_term_to_heap(&term, &mut self.heap, &self.atom_tbl)
+        write_term_to_heap(&term, &mut self.heap)
     }
 }
 
@@ -295,16 +296,14 @@ impl CharRead for ReadlineStream {
 pub(crate) fn write_term_to_heap(
     term: &Term,
     heap: &mut Heap,
-    atom_tbl: &AtomTable,
 ) -> Result<TermWriteResult, CompilationError> {
-    let term_writer = TermWriter::new(heap, atom_tbl);
+    let term_writer = TermWriter::new(heap);
     term_writer.write_term_to_heap(term)
 }
 
 #[derive(Debug)]
-struct TermWriter<'a, 'b> {
+struct TermWriter<'a> {
     heap: &'a mut Heap,
-    atom_tbl: &'b AtomTable,
     queue: SubtermDeque,
     var_dict: HeapVarDict,
 }
@@ -315,12 +314,11 @@ pub struct TermWriteResult {
     pub var_dict: HeapVarDict,
 }
 
-impl<'a, 'b> TermWriter<'a, 'b> {
+impl<'a> TermWriter<'a> {
     #[inline]
-    fn new(heap: &'a mut Heap, atom_tbl: &'b AtomTable) -> Self {
+    fn new(heap: &'a mut Heap) -> Self {
         TermWriter {
             heap,
-            atom_tbl,
             queue: SubtermDeque::new(),
             var_dict: HeapVarDict::with_hasher(FxBuildHasher::default()),
         }
@@ -338,25 +336,23 @@ impl<'a, 'b> TermWriter<'a, 'b> {
     }
 
     #[inline]
-    fn push_stub_addr(&mut self) {
+    fn push_stub_addr(&mut self) -> Result<(), CompilationError> {
-        let h = self.heap.len();
+        let h = self.heap.cell_len();
-        self.heap.push(heap_loc_as_cell!(h));
+        self.push_cell(heap_loc_as_cell!(h))
+    }
+
+    #[inline]
+    fn push_cell(&mut self, cell: HeapCellValue) -> Result<(), CompilationError> {
+        self.heap
+            .push_cell(cell)
+            .map_err(CompilationError::FiniteMemoryInHeap)
     }
 
     fn term_as_addr(&mut self, term: &TermRef, h: usize) -> HeapCellValue {
         match term {
             &TermRef::Cons(..) => list_loc_as_cell!(h),
             &TermRef::AnonVar(_) | &TermRef::Var(..) => heap_loc_as_cell!(h),
-            TermRef::CompleteString(_, _, src) => {
+            TermRef::PartialString(..) | TermRef::CompleteString(..) => heap_loc_as_cell!(h),
-                if src.as_str().is_empty() {
-                    empty_list_as_cell!()
-                } else if self.heap[h].get_tag() == HeapCellValueTag::CStr {
-                    heap_loc_as_cell!(h)
-                } else {
-                    pstr_loc_as_cell!(h)
-                }
-            }
-            &TermRef::PartialString(..) => pstr_loc_as_cell!(h),
             &TermRef::Literal(_, _, literal) => HeapCellValue::from(*literal),
             &TermRef::Clause(_, _, _, subterms) if subterms.is_empty() => heap_loc_as_cell!(h),
             &TermRef::Clause(..) => str_loc_as_cell!(h),
@@ -364,45 +360,45 @@ impl<'a, 'b> TermWriter<'a, 'b> {
     }
 
     fn write_term_to_heap(mut self, term: &Term) -> Result<TermWriteResult, CompilationError> {
-        let heap_loc = self.heap.len();
+        let heap_loc = self.heap.cell_len();
 
         for term in breadth_first_iter(term, RootIterationPolicy::Iterated) {
-            let h = self.heap.len();
+            let h = self.heap.cell_len();
 
             match &term {
                 &TermRef::Cons(Level::Root, ..) => {
                     self.queue.push_back((2, h + 1));
-                    self.heap.push(list_loc_as_cell!(h + 1));
+                    self.push_cell(list_loc_as_cell!(h + 1))?;
 
-                    self.push_stub_addr();
+                    self.push_stub_addr()?;
-                    self.push_stub_addr();
+                    self.push_stub_addr()?;
 
                     continue;
                 }
                 &TermRef::Cons(..) => {
                     self.queue.push_back((2, h));
 
-                    self.push_stub_addr();
+                    self.push_stub_addr()?;
-                    self.push_stub_addr();
+                    self.push_stub_addr()?;
                 }
                 &TermRef::Clause(Level::Root, _, name, subterms) => {
                     if subterms.len() > MAX_ARITY {
                         return Err(CompilationError::ExceededMaxArity);
                     }
 
-                    self.heap.push(if subterms.is_empty() {
+                    self.push_cell(if subterms.is_empty() {
                         heap_loc_as_cell!(heap_loc + 1)
                     } else {
                         str_loc_as_cell!(heap_loc + 1)
-                    });
+                    })?;
 
                     self.queue.push_back((subterms.len(), h + 2));
                     let named = atom_as_cell!(name, subterms.len());
 
-                    self.heap.push(named);
+                    self.push_cell(named)?;
 
                     for _ in 0..subterms.len() {
-                        self.push_stub_addr();
+                        self.push_stub_addr()?;
                     }
 
                     continue;
@@ -411,20 +407,20 @@ impl<'a, 'b> TermWriter<'a, 'b> {
                     self.queue.push_back((subterms.len(), h + 1));
                     let named = atom_as_cell!(name, subterms.len());
 
-                    self.heap.push(named);
+                    self.push_cell(named)?;
 
                     for _ in 0..subterms.len() {
-                        self.push_stub_addr();
+                        self.push_stub_addr()?;
                     }
                 }
                 &TermRef::AnonVar(Level::Root) | TermRef::Literal(Level::Root, ..) => {
                     let addr = self.term_as_addr(&term, h);
-                    self.heap.push(addr);
+                    self.push_cell(addr)?;
                 }
                 &TermRef::Var(Level::Root, _, ref var_ptr) => {
                     let addr = self.term_as_addr(&term, h);
                     self.var_dict.insert(VarKey::VarPtr(var_ptr.clone()), addr);
-                    self.heap.push(addr);
+                    self.push_cell(addr)?;
                 }
                 &TermRef::AnonVar(_) => {
                     if let Some((arity, site_h)) = self.queue.pop_front() {
@@ -438,25 +434,53 @@ impl<'a, 'b> TermWriter<'a, 'b> {
 
                     continue;
                 }
-                TermRef::CompleteString(_, _, src) => {
+                TermRef::CompleteString(lvl, _, src) => {
-                    let src = src.as_str().to_owned();
+                    if let Level::Root = lvl {
-                    put_complete_string(self.heap, &src, self.atom_tbl);
+                        self.push_stub_addr()?;
+                    }
+
+                    let cell = self
+                        .heap
+                        .allocate_cstr(src)
+                        .map_err(CompilationError::FiniteMemoryInHeap)?;
+
+                    let new_h = self.heap.cell_len();
+                    self.push_cell(cell)?;
+
+                    if !matches!(lvl, Level::Root) {
+                        self.modify_head_of_queue(&term, new_h);
+                    } else {
+                        self.heap[h] = cell;
+                    }
+
+                    continue;
                 }
-                &TermRef::PartialString(lvl, _, src, _) => {
+                TermRef::PartialString(lvl, _, src, _) => {
                     if let Level::Root = lvl {
-                        // Var tags can't refer directly to partial strings,
+                        self.push_stub_addr()?;
-                        // so a PStrLoc cell must be pushed.
-                        self.heap.push(pstr_loc_as_cell!(heap_loc + 1));
                     }
 
-                    allocate_pstr(self.heap, src.as_str(), self.atom_tbl);
+                    let cell = self
+                        .heap
+                        .allocate_pstr(src)
+                        .map_err(CompilationError::FiniteMemoryInHeap)?;
 
-                    let h = self.heap.len();
+                    let tail_h = self.heap.cell_len();
-                    self.queue.push_back((1, h - 1));
+                    self.push_stub_addr()?;
 
-                    if let Level::Root = lvl {
+                    if matches!(lvl, Level::Root) {
-                        continue;
+                        self.heap[h] = cell;
+                    } else {
+                        self.push_cell(cell)?;
+                    };
+
+                    self.queue.push_back((1, tail_h));
+
+                    if !matches!(lvl, Level::Root) {
+                        self.modify_head_of_queue(&term, tail_h + 1);
                     }
+
+                    continue;
                 }
                 TermRef::Var(.., var) => {
                     if let Some((arity, site_h)) = self.queue.pop_front() {

src/targets.rs

@@ -6,6 +6,8 @@ use crate::instructions::*;
 use crate::iterators::*;
 use crate::types::*;
 
+use std::rc::Rc;
+
 pub(crate) struct FactInstruction;
 pub(crate) struct QueryInstruction;
 
@@ -14,14 +16,14 @@ pub(crate) trait CompilationTarget<'a> {
 
     fn iter(term: &'a Term) -> Self::Iterator;
 
-    fn to_constant(lvl: Level, literal: Literal, r: RegType) -> Instruction;
+    fn to_constant(lvl: Level, constant: Literal, r: RegType) -> Instruction;
     fn to_list(lvl: Level, r: RegType) -> Instruction;
     fn to_structure(lvl: Level, name: Atom, arity: usize, r: RegType) -> Instruction;
 
     fn to_void(num_subterms: usize) -> Instruction;
     fn is_void_instr(instr: &Instruction) -> bool;
 
-    fn to_pstr(lvl: Level, string: Atom, r: RegType, has_tail: bool) -> Instruction;
+    fn to_pstr(lvl: Level, string: Rc<String>, r: RegType) -> Instruction;
 
     fn incr_void_instr(instr: &mut Instruction);
 
@@ -67,8 +69,8 @@ impl<'a> CompilationTarget<'a> for FactInstruction {
         matches!(instr, &Instruction::UnifyVoid(_))
     }
 
-    fn to_pstr(lvl: Level, string: Atom, r: RegType, has_tail: bool) -> Instruction {
+    fn to_pstr(lvl: Level, string: Rc<String>, r: RegType) -> Instruction {
-        Instruction::GetPartialString(lvl, string, r, has_tail)
+        Instruction::GetPartialString(lvl, string, r)
     }
 
     fn incr_void_instr(instr: &mut Instruction) {
@@ -125,16 +127,12 @@ impl<'a> CompilationTarget<'a> for QueryInstruction {
         Instruction::PutStructure(name, arity, r)
     }
 
-    fn to_constant(lvl: Level, constant: Literal, reg: RegType) -> Instruction {
-        Instruction::PutConstant(lvl, HeapCellValue::from(constant), reg)
-    }
-
     fn to_list(lvl: Level, reg: RegType) -> Instruction {
         Instruction::PutList(lvl, reg)
     }
 
-    fn to_pstr(lvl: Level, string: Atom, r: RegType, has_tail: bool) -> Instruction {
+    fn to_pstr(lvl: Level, string: Rc<String>, r: RegType) -> Instruction {
-        Instruction::PutPartialString(lvl, string, r, has_tail)
+        Instruction::PutPartialString(lvl, string, r)
     }
 
     fn to_void(subterms: usize) -> Instruction {
@@ -155,6 +153,10 @@ impl<'a> CompilationTarget<'a> for QueryInstruction {
         Instruction::SetConstant(HeapCellValue::from(constant))
     }
 
+    fn to_constant(lvl: Level, constant: Literal, reg: RegType) -> Instruction {
+        Instruction::PutConstant(lvl, HeapCellValue::from(constant), reg)
+    }
+
     fn argument_to_variable(arg: RegType, val: usize) -> Instruction {
         Instruction::PutVariable(arg, val)
     }

src/types.rs

@@ -3,10 +3,12 @@
 use crate::arena::*;
 use crate::atom_table::*;
 use crate::forms::*;
+use crate::machine::heap::*;
 use crate::machine::machine_indices::*;
-use crate::machine::partial_string::PartialString;
 use crate::machine::streams::*;
+use crate::offset_table::*;
 use crate::parser::ast::Fixnum;
+use crate::parser::ast::Literal;
 
 use std::cmp::Ordering;
 use std::convert::TryFrom;
@@ -14,60 +16,67 @@ use std::fmt;
 use std::mem;
 use std::ops::{Add, Sub, SubAssign};
 
+use dashu::{Integer, Rational};
+
 #[derive(BitfieldSpecifier, Copy, Clone, Debug, PartialEq, Eq, PartialOrd, Ord)]
+#[repr(u8)]
 #[bits = 6]
 pub enum HeapCellValueTag {
-    Str = 0b000011,
+    Str = 0b000001,
     Lis = 0b000101,
-    Var = 0b000111,
+    Var = 0b001011,
-    StackVar = 0b001001,
+    StackVar = 0b001101,
-    AttrVar = 0b001011,
+    AttrVar = 0b010001,
-    PStrLoc = 0b001101,
+    PStrLoc = 0b010011,
-    PStrOffset = 0b001111,
     // constants.
     Cons = 0b0,
-    F64 = 0b010001,
+    F64Offset = 0b010101,
-    Fixnum = 0b010011,
+    Fixnum = 0b011001,
-    Char = 0b010101,
+    CodeIndexOffset = 0b011011,
-    Atom = 0b010111,
+    Atom = 0b011111,
-    PStr = 0b011001,
+    CutPoint = 0b011101,
-    CStr = 0b011011,
+    // trail elements.
-    CutPoint = 0b011111,
+    TrailedHeapVar = 0b100001,
+    TrailedStackVar = 0b100011,
+    TrailedAttrVar = 0b100101,
+    TrailedAttrVarListLink = 0b101001,
+    TrailedAttachedValue = 0b101011,
+    TrailedBlackboardEntry = 0b101101,
+    TrailedBlackboardOffset = 0b110001,
 }
 
 #[derive(BitfieldSpecifier, Copy, Clone, Debug, PartialEq, Eq, PartialOrd, Ord)]
+#[repr(u8)]
 #[bits = 6]
 pub enum HeapCellValueView {
-    Str = 0b000011,
+    Str = 0b000001,
     Lis = 0b000101,
-    Var = 0b000111,
+    Var = 0b001011,
-    StackVar = 0b001001,
+    StackVar = 0b001101,
-    AttrVar = 0b001011,
+    AttrVar = 0b010001,
-    PStrLoc = 0b001101,
+    PStrLoc = 0b010011,
-    PStrOffset = 0b001111,
     // constants.
     Cons = 0b0,
-    F64 = 0b010001,
+    F64Offset = 0b010101,
-    Fixnum = 0b010011,
+    Fixnum = 0b011001,
-    Char = 0b010101,
+    CodeIndexOffset = 0b011011,
-    Atom = 0b010111,
+    Atom = 0b011111,
-    PStr = 0b011001,
+    CutPoint = 0b011101,
-    CStr = 0b011011,
-    CutPoint = 0b011111,
     // trail elements.
-    TrailedHeapVar = 0b101111,
+    TrailedHeapVar = 0b100001,
-    TrailedStackVar = 0b101011,
+    TrailedStackVar = 0b100011,
-    TrailedAttrVar = 0b100001,
+    TrailedAttrVar = 0b100101,
-    TrailedAttrVarListLink = 0b100011,
+    TrailedAttrVarListLink = 0b101001,
-    TrailedAttachedValue = 0b100101,
+    TrailedAttachedValue = 0b101011,
-    TrailedBlackboardEntry = 0b100111,
+    TrailedBlackboardEntry = 0b101101,
-    TrailedBlackboardOffset = 0b110011,
+    TrailedBlackboardOffset = 0b110001,
 }
 
 #[derive(BitfieldSpecifier, Copy, Clone, Debug, PartialEq, Eq, PartialOrd, Ord)]
 #[bits = 1]
 pub enum ConsPtrMaskTag {
     Cons = 0b0,
+    Atom = 0b1,
 }
 
 #[bitfield]
@@ -84,7 +93,7 @@ impl ConsPtr {
     #[inline(always)]
     pub fn build_with(ptr: *const ArenaHeader, tag: ConsPtrMaskTag) -> Self {
         ConsPtr::new()
-            .with_ptr(ptr as *const u8 as u64)
+            .with_ptr(ptr.expose_provenance() as u64)
             .with_f(false)
             .with_m(false)
             .with_tag(tag)
@@ -93,7 +102,7 @@ impl ConsPtr {
     #[inline(always)]
     pub fn as_ptr(self) -> *mut u8 {
         let addr: u64 = self.ptr();
-        addr as usize as *mut _
+        std::ptr::with_exposed_provenance_mut(addr as usize)
     }
 
     #[inline(always)]
@@ -105,9 +114,9 @@ impl ConsPtr {
 #[derive(BitfieldSpecifier, Copy, Clone, Debug)]
 #[bits = 6]
 pub(crate) enum RefTag {
-    HeapCell = 0b000111,
+    HeapCell = 0b001011,
-    StackCell = 0b001001,
+    StackCell = 0b001101,
-    AttrVar = 0b001011,
+    AttrVar = 0b010001,
 }
 
 #[bitfield]
@@ -245,15 +254,16 @@ pub struct HeapCellValue {
     val: B56,
     f: bool,
     m: bool,
+    #[allow(dead_code)]
     tag: HeapCellValueTag,
 }
 
 impl fmt::Debug for HeapCellValue {
     fn fmt(&self, f: &mut std::fmt::Formatter) -> fmt::Result {
         match self.get_tag() {
-            HeapCellValueTag::F64 => f
+            HeapCellValueTag::F64Offset => f
                 .debug_struct("HeapCellValue")
-                .field("tag", &HeapCellValueTag::F64)
+                .field("tag", &HeapCellValueTag::F64Offset)
                 .field("offset", &self.get_value())
                 .field("m", &self.m())
                 .field("f", &self.f())
@@ -279,16 +289,6 @@ impl fmt::Debug for HeapCellValue {
                     .field("f", &self.f())
                     .finish()
             }
-            HeapCellValueTag::PStr => {
-                let (name, _) = cell_as_atom_cell!(self).get_name_and_arity();
-
-                f.debug_struct("HeapCellValue")
-                    .field("tag", &HeapCellValueTag::PStr)
-                    .field("contents", &name.as_str())
-                    .field("m", &self.m())
-                    .field("f", &self.f())
-                    .finish()
-            }
             tag => f
                 .debug_struct("HeapCellValue")
                 .field("tag", &tag)
@@ -300,20 +300,89 @@ impl fmt::Debug for HeapCellValue {
     }
 }
 
+impl From<Literal> for HeapCellValue {
+    #[inline]
+    fn from(literal: Literal) -> Self {
+        match literal {
+            Literal::Atom(name) => atom_as_cell!(name),
+            Literal::CodeIndexOffset(idx) => HeapCellValue::from(idx),
+            Literal::Fixnum(n) => fixnum_as_cell!(n),
+            Literal::Integer(bigint_ptr) => {
+                typed_arena_ptr_as_cell!(bigint_ptr)
+            }
+            Literal::Rational(bigint_ptr) => {
+                typed_arena_ptr_as_cell!(bigint_ptr)
+            }
+            Literal::F64Offset(f) => HeapCellValue::from(f),
+        }
+    }
+}
+
+impl TryFrom<HeapCellValue> for Literal {
+    type Error = ();
+
+    fn try_from(value: HeapCellValue) -> Result<Literal, ()> {
+        read_heap_cell!(value,
+            (HeapCellValueTag::Atom, (name, arity)) => {
+                if arity == 0 {
+                    Ok(Literal::Atom(name))
+                } else {
+                    Err(())
+                }
+            }
+            (HeapCellValueTag::Fixnum, n) => {
+                Ok(Literal::Fixnum(n))
+            }
+            (HeapCellValueTag::F64Offset, f) => {
+                Ok(Literal::F64Offset(f))
+            }
+            (HeapCellValueTag::CodeIndexOffset, idx) => {
+                Ok(Literal::CodeIndexOffset(idx))
+            }
+            (HeapCellValueTag::Cons, cons_ptr) => {
+                match_untyped_arena_ptr!(cons_ptr,
+                     (ArenaHeaderTag::Integer, n) => {
+                         Ok(Literal::Integer(n))
+                     }
+                     (ArenaHeaderTag::Rational, n) => {
+                         Ok(Literal::Rational(n))
+                     }
+                     _ => {
+                         Err(())
+                     }
+                )
+            }
+            _ => {
+                Err(())
+            }
+        )
+    }
+}
+
 impl<T: ArenaAllocated> From<TypedArenaPtr<T>> for HeapCellValue
 where
     T::Payload: Sized,
 {
     #[inline]
     fn from(arena_ptr: TypedArenaPtr<T>) -> HeapCellValue {
-        HeapCellValue::from(arena_ptr.header_ptr() as u64)
+        HeapCellValue::from(arena_ptr.header_ptr().expose_provenance() as u64)
     }
 }
 
-impl From<F64Ptr> for HeapCellValue {
+impl From<F64Offset> for HeapCellValue {
     #[inline]
-    fn from(f64_ptr: F64Ptr) -> HeapCellValue {
+    fn from(f64_offset: F64Offset) -> HeapCellValue {
-        HeapCellValue::build_with(HeapCellValueTag::F64, f64_ptr.as_offset().to_u64())
+        HeapCellValue::build_with(HeapCellValueTag::F64Offset, f64_offset.to_u64())
+    }
+}
+
+impl From<CodeIndexOffset> for HeapCellValue {
+    #[inline]
+    fn from(code_index_offset: CodeIndexOffset) -> HeapCellValue {
+        HeapCellValue::build_with(
+            HeapCellValueTag::CodeIndexOffset,
+            code_index_offset.to_u64(),
+        )
     }
 }
 
@@ -321,7 +390,7 @@ impl From<ConsPtr> for HeapCellValue {
     #[inline(always)]
     fn from(cons_ptr: ConsPtr) -> HeapCellValue {
         HeapCellValue::from_bytes(
-            ConsPtr::from(cons_ptr.as_ptr() as u64)
+            ConsPtr::from(cons_ptr.as_ptr().expose_provenance() as u64)
                 .with_tag(ConsPtrMaskTag::Cons)
                 .with_m(false)
                 .into_bytes(),
@@ -354,19 +423,15 @@ impl HeapCellValue {
     }
 
     #[inline]
-    pub fn is_string_terminator(mut self, heap: &[HeapCellValue]) -> bool {
+    pub fn is_string_terminator(mut self, heap: &impl SizedHeap) -> bool {
-        use crate::machine::heap::*;
-
         loop {
             return read_heap_cell!(self,
                 (HeapCellValueTag::Atom, (name, arity)) => {
                     name == atom!("[]") && arity == 0
                 }
-                (HeapCellValueTag::CStr) => {
-                    true
-                }
                 (HeapCellValueTag::PStrLoc, h) => {
-                    self = heap[h];
+                    let HeapStringScan { tail_idx, .. } = heap.scan_slice_to_str(h);
+                    self = heap[tail_idx];
                     continue;
                 }
                 (HeapCellValueTag::AttrVar | HeapCellValueTag::Var, h) => {
@@ -379,9 +444,6 @@ impl HeapCellValue {
                     self = cell;
                     continue;
                 }
-                (HeapCellValueTag::PStrOffset, pstr_offset) => {
-                    heap[pstr_offset].get_tag() == HeapCellValueTag::CStr
-                }
                 _ => {
                     false
                 }
@@ -399,16 +461,12 @@ impl HeapCellValue {
                 | HeapCellValueTag::StackVar
                 | HeapCellValueTag::AttrVar
                 | HeapCellValueTag::PStrLoc
-                | HeapCellValueTag::PStrOffset
         )
     }
 
     #[inline]
     pub fn as_char(self) -> Option<char> {
         read_heap_cell!(self,
-            (HeapCellValueTag::Char, c) => {
-                Some(c)
-            }
             (HeapCellValueTag::Atom, (name, arity)) => {
                 if arity > 0 {
                     return None;
@@ -426,11 +484,9 @@ impl HeapCellValue {
     pub fn is_constant(self) -> bool {
         match self.get_tag() {
             HeapCellValueTag::Cons
-            | HeapCellValueTag::F64
+            | HeapCellValueTag::F64Offset
             | HeapCellValueTag::Fixnum
-            | HeapCellValueTag::CutPoint
+            | HeapCellValueTag::CutPoint => true,
-            | HeapCellValueTag::Char
-            | HeapCellValueTag::CStr => true,
             HeapCellValueTag::Atom => cell_as_atom_cell!(self).get_arity() == 0,
             _ => false,
         }
@@ -442,16 +498,12 @@ impl HeapCellValue {
     }
 
     #[inline]
-    pub fn is_compound(self, heap: &[HeapCellValue]) -> bool {
+    pub fn is_compound(self, heap: &Heap) -> bool {
         match self.get_tag() {
             HeapCellValueTag::Str => {
                 cell_as_atom_cell!(heap[self.get_value() as usize]).get_arity() > 0
             }
-            HeapCellValueTag::Lis
+            HeapCellValueTag::Lis | HeapCellValueTag::PStrLoc => true,
-            | HeapCellValueTag::CStr
-            | HeapCellValueTag::PStr
-            | HeapCellValueTag::PStrLoc
-            | HeapCellValueTag::PStrOffset => true,
             HeapCellValueTag::Atom => cell_as_atom_cell!(self).get_arity() > 0,
             _ => false,
         }
@@ -502,6 +554,7 @@ impl HeapCellValue {
         match self.tag_or_err() {
             Ok(tag) => tag,
             Err(_) => match ConsPtr::from_bytes(self.into_bytes()).tag() {
+                ConsPtrMaskTag::Atom => HeapCellValueTag::Atom,
                 ConsPtrMaskTag::Cons => HeapCellValueTag::Cons,
             },
         }
@@ -509,16 +562,8 @@ impl HeapCellValue {
 
     #[inline]
     pub fn to_atom(self) -> Option<Atom> {
-        match self.tag() {
+        match self.get_tag() {
-            HeapCellValueTag::Atom => Some(Atom::from(self.val() << 3)),
+            HeapCellValueTag::Atom => Some(AtomCell::from_bytes(self.into_bytes()).get_name()),
-            _ => None,
-        }
-    }
-
-    #[inline]
-    pub fn to_pstr(self) -> Option<PartialString> {
-        match self.tag() {
-            HeapCellValueTag::PStr => Some(PartialString::from(Atom::from(self.val() << 3))),
             _ => None,
         }
     }
@@ -531,6 +576,16 @@ impl HeapCellValue {
         }
     }
 
+    // FIXME: someone that knows this better should check if this can be split into `to_fixnum_unchecked` and `to_cut_point_unchecked` assuming thats always unambigusly knowable
+    #[inline]
+    pub unsafe fn to_fixnum_or_cut_point_unchecked(self) -> Fixnum {
+        debug_assert!(matches!(
+            self.get_tag(),
+            HeapCellValueTag::Fixnum | HeapCellValueTag::CutPoint
+        ));
+        Fixnum::from_bytes(self.into_bytes())
+    }
+
     #[inline]
     pub fn from_ptr_addr(ptr_bytes: usize) -> Self {
         HeapCellValue::from_bytes((ptr_bytes as u64).to_ne_bytes())
@@ -593,38 +648,53 @@ impl HeapCellValue {
         }
     }
 
-    pub fn order_category(self, heap: &[HeapCellValue]) -> Option<TermOrderCategory> {
+    pub fn order_category(self, heap: &Heap) -> Option<TermOrderCategory> {
-        match Number::try_from(self).ok() {
+        read_heap_cell!(self,
-            Some(Number::Integer(_)) | Some(Number::Fixnum(_)) | Some(Number::Rational(_)) => {
+            (HeapCellValueTag::Cons, c) => {
+                match_untyped_arena_ptr!(c,
+                   (ArenaHeaderTag::Integer, _n) => {
+                       Some(TermOrderCategory::Integer)
+                   }
+                   (ArenaHeaderTag::Rational, _n) => {
+                       Some(TermOrderCategory::Integer)
+                   }
+                   _ => {
+                       None
+                   }
+                )
+            }
+            (HeapCellValueTag::F64Offset) => {
+                Some(TermOrderCategory::FloatingPoint)
+            }
+            (HeapCellValueTag::Fixnum | HeapCellValueTag::CutPoint) => {
                 Some(TermOrderCategory::Integer)
             }
-            Some(Number::Float(_)) => Some(TermOrderCategory::FloatingPoint),
+            (HeapCellValueTag::Var | HeapCellValueTag::StackVar | HeapCellValueTag::AttrVar) => {
-            None => match self.get_tag() {
+                Some(TermOrderCategory::Variable)
-                HeapCellValueTag::Var | HeapCellValueTag::StackVar | HeapCellValueTag::AttrVar => {
+            }
-                    Some(TermOrderCategory::Variable)
+            (HeapCellValueTag::Atom, (_name, arity)) => {
-                }
+                Some(if arity > 0 {
-                HeapCellValueTag::Char => Some(TermOrderCategory::Atom),
-                HeapCellValueTag::Atom => Some(if cell_as_atom_cell!(self).get_arity() > 0 {
                     TermOrderCategory::Compound
                 } else {
                     TermOrderCategory::Atom
-                }),
+                })
-                HeapCellValueTag::Lis | HeapCellValueTag::PStrLoc | HeapCellValueTag::CStr => {
+            }
+            (HeapCellValueTag::Lis | HeapCellValueTag::PStrLoc) => {
+                Some(TermOrderCategory::Compound)
+            }
+            (HeapCellValueTag::Str, s) => {
+                let arity = cell_as_atom_cell!(heap[s]).get_arity();
+
+                if arity == 0 {
+                    Some(TermOrderCategory::Atom)
+                } else {
                     Some(TermOrderCategory::Compound)
                 }
-                HeapCellValueTag::Str => {
+            }
-                    let value = heap[self.get_value() as usize];
+            _ => {
-                    let arity = cell_as_atom_cell!(value).get_arity();
+                None
-
+            }
-                    if arity == 0 {
+        )
-                        Some(TermOrderCategory::Atom)
-                    } else {
-                        Some(TermOrderCategory::Compound)
-                    }
-                }
-                _ => None,
-            },
-        }
     }
 
     #[inline(always)]
@@ -640,7 +710,7 @@ impl HeapCellValue {
     }
 }
 
-const_assert!(mem::size_of::<HeapCellValue>() == 8);
+const_assert!(size_of::<HeapCellValue>() == 8);
 
 #[bitfield]
 #[repr(u64)]
@@ -666,21 +736,21 @@ const_assert!(mem::size_of::<UntypedArenaPtr>() == 8);
 impl From<*const ArenaHeader> for UntypedArenaPtr {
     #[inline]
     fn from(ptr: *const ArenaHeader) -> UntypedArenaPtr {
-        UntypedArenaPtr::build_with(ptr as usize)
+        UntypedArenaPtr::build_with(ptr.expose_provenance())
     }
 }
 
 impl From<*const IndexPtr> for UntypedArenaPtr {
     #[inline]
     fn from(ptr: *const IndexPtr) -> UntypedArenaPtr {
-        UntypedArenaPtr::build_with(ptr as usize)
+        UntypedArenaPtr::build_with(ptr.expose_provenance())
     }
 }
 
 impl From<UntypedArenaPtr> for *const ArenaHeader {
     #[inline]
     fn from(ptr: UntypedArenaPtr) -> *const ArenaHeader {
-        ptr.get_ptr() as *const ArenaHeader
+        ptr.get_ptr().cast::<ArenaHeader>()
     }
 }
 
@@ -693,21 +763,21 @@ impl UntypedArenaPtr {
     #[inline]
     pub fn get_ptr(self) -> *const u8 {
         let addr: u64 = self.ptr();
-        addr as usize as *const u8
+        std::ptr::with_exposed_provenance(addr as usize)
     }
 
     #[inline]
     pub fn get_tag(self) -> ArenaHeaderTag {
         unsafe {
             debug_assert!(!self.get_ptr().is_null());
-            let header = *(self.get_ptr() as *const ArenaHeader);
+            let header = *self.get_ptr().cast::<ArenaHeader>();
             header.get_tag()
         }
     }
 
     #[inline]
     pub fn payload_offset(self) -> *const u8 {
-        unsafe { self.get_ptr().add(mem::size_of::<ArenaHeader>()) }
+        unsafe { self.get_ptr().add(size_of::<ArenaHeader>()) }
     }
 
     /// # Safety
@@ -734,12 +804,14 @@ impl Add<usize> for HeapCellValue {
         match self.get_tag() {
             tag @ HeapCellValueTag::Str
             | tag @ HeapCellValueTag::Lis
-            | tag @ HeapCellValueTag::PStrOffset
-            | tag @ HeapCellValueTag::PStrLoc
             | tag @ HeapCellValueTag::Var
             | tag @ HeapCellValueTag::AttrVar => {
                 HeapCellValue::build_with(tag, (self.get_value() as usize + rhs) as u64)
             }
+            tag @ HeapCellValueTag::PStrLoc => {
+                let value = (self.get_value() as usize + heap_index!(rhs)) as u64;
+                HeapCellValue::build_with(tag, value)
+            }
             _ => self,
         }
     }
@@ -752,12 +824,14 @@ impl Sub<usize> for HeapCellValue {
         match self.get_tag() {
             tag @ HeapCellValueTag::Str
             | tag @ HeapCellValueTag::Lis
-            | tag @ HeapCellValueTag::PStrOffset
-            | tag @ HeapCellValueTag::PStrLoc
             | tag @ HeapCellValueTag::Var
             | tag @ HeapCellValueTag::AttrVar => {
                 HeapCellValue::build_with(tag, (self.get_value() as usize - rhs) as u64)
             }
+            tag @ HeapCellValueTag::PStrLoc => {
+                let value = self.get_value() as usize - heap_index!(rhs);
+                HeapCellValue::build_with(tag, value as u64)
+            }
             _ => self,
         }
     }
@@ -778,12 +852,15 @@ impl Sub<i64> for HeapCellValue {
             match self.get_tag() {
                 tag @ HeapCellValueTag::Str
                 | tag @ HeapCellValueTag::Lis
-                | tag @ HeapCellValueTag::PStrOffset
-                | tag @ HeapCellValueTag::PStrLoc
                 | tag @ HeapCellValueTag::Var
                 | tag @ HeapCellValueTag::AttrVar => {
                     HeapCellValue::build_with(tag, self.get_value() + rhs.unsigned_abs())
                 }
+                tag @ HeapCellValueTag::PStrLoc => {
+                    let value =
+                        self.get_value() as usize + heap_index!(rhs.unsigned_abs() as usize);
+                    HeapCellValue::build_with(tag, value as u64)
+                }
                 _ => self,
             }
         } else {

src/variable_records.rs

@@ -1,3 +1,4 @@
+use crate::forms::GenContext;
 use crate::parser::ast::*;
 
 use bit_set::*;

tests-pl/invalid_decl11.pl

@@ -1 +1 @@
-:- op(10, xf, [example, Var]).
+:- op(10, xf, [example, Var]).

tests-pl/issue2588.pl

@@ -2,4 +2,4 @@
 
 test :- load_html("<html><head><title>Hello!</title></head></html>", Es, []), write(Es).
 
-:- initialization(test).
+:- initialization(test).

tests-pl/issue2949.pl

@@ -0,0 +1,11 @@
+:- use_module(library(sgml)).
+
+test :- 
+    load_html("<!DOCTYPE html><html><head><title>Hello!</title></head></html>", Es, []), 
+    write(Es),
+    load_html("<!DOCTYPE html><html><head><title>Hello!</title><!-- comment --></head></html>", Es2, []), 
+    write(Es2),
+    load_html("<!", Es3, []), 
+    write(Es3).
+
+:- initialization(test).

tests/scryer/cli/src_tests/all_modules.stdin

@@ -27,6 +27,7 @@ use_module(library(ordsets)).
 use_module(library(os)).
 use_module(library(pairs)).
 use_module(library(pio)).
+use_module(library(process)).
 use_module(library(queues)).
 use_module(library(random)).
 use_module(library(reif)).

tests/scryer/cli/src_tests/all_modules.stdout

@@ -45,3 +45,4 @@
    true.
    true.
    true.
+   true.

tests/scryer/cli/src_tests/process.md

@@ -0,0 +1,59 @@
+```trycmd
+$ scryer-prolog -f --no-add-history -g 'use_module(library(process)), process_create("", [], [invalid, process(P)]), process_kill(P), halt'
+use_module(library(process)),process_create([],[],[invalid,process(P)]),process_kill(P),halt causes: error(domain_error(process_create_option,invalid),[predicate-process_create/3,predicate-check_options/3,predicate-must_be_known_options/3])
+
+```
+
+```trycmd
+$ scryer-prolog -f --no-add-history -g 'use_module(library(process)), process_create("", [], [invalid(_Var), process(P)]), process_kill(P), halt'
+use_module(library(process)),process_create([],[],[invalid(_Var),process(P)]),process_kill(P),halt causes: error(domain_error(process_create_option,invalid),[predicate-process_create/3,predicate-check_options/3,predicate-must_be_known_options/3])
+
+```
+
+```trycmd
+$ scryer-prolog -f --no-add-history -g 'use_module(library(process)), process_create("", [], [stdin(null), stdin(null), process(P)]), process_kill(P), halt'
+use_module(library(process)),process_create([],[],[stdin(null),stdin(null),process(P)]),process_kill(P),halt causes: error(domain_error(non_duplicate_options,stdin),[predicate-process_create/3,predicate-check_options/3,predicate-must_be_known_options/3])
+
+```
+
+```trycmd
+$ scryer-prolog -f --no-add-history -g 'use_module(library(process)), process_create("", [], [env([]), environment([]), process(P)]), process_kill(P), halt'
+use_module(library(process)),process_create([],[],[env([]),environment([]),process(P)]),process_kill(P),halt causes: error(domain_error(non_conflicting_options,[env([]),environment([])]),[predicate-process_create/3,predicate-check_options/3,predicate-extract_options/2])
+
+```
+
+```trycmd
+$ scryer-prolog -f --no-add-history -g 'use_module(library(process)), process_wait(pid, _Status, [invalid(_Var), timeout(0)]), halt'
+use_module(library(process)),process_wait(pid,_Status,[invalid(_Var),timeout(0)]),halt causes: error(domain_error(process_wait_option,invalid),[predicate-process_wait/3,predicate-check_options/3,predicate-must_be_known_options/3])
+
+```
+
+```trycmd
+$ scryer-prolog -f --no-add-history -g 'use_module(library(process)), process_create("", [], [stdin(invalid), process(P)]), process_kill(P), halt'
+use_module(library(process)),process_create([],[],[stdin(invalid),process(P)]),process_kill(P),halt causes: error(domain_error(stdio_spec,invalid),[predicate-process_create/3,predicate-check_options/3,predicate-extract_options/2,predicate-valid_stdio/1])
+
+```
+
+```trycmd
+$ scryer-prolog -f --no-add-history -g 'use_module(library(process)), process_wait(50, _Status), halt'
+use_module(library(process)),process_wait(50,_Status),halt causes: error(type_error(process,50),[predicate-process_wait/2,predicate-process_wait/3|process_wait/3])
+
+```
+
+```trycmd
+$ scryer-prolog -f --no-add-history -g 'use_module(library(process)), process_kill(50), halt'
+use_module(library(process)),process_kill(50),halt causes: error(type_error(process,50),[predicate-process_kill/1|process_kill/1])
+
+```
+
+```trycmd
+$ scryer-prolog -f --no-add-history -g 'use_module(library(process)), process_id(50,_Pid), halt'
+use_module(library(process)),process_id(50,_Pid),halt causes: error(type_error(process,50),[predicate-process_id/2|process_id/2])
+
+```
+
+```trycmd
+$ scryer-prolog -f --no-add-history -g 'use_module(library(process)), process_release(50), halt'
+use_module(library(process)),process_release(50),halt causes: error(type_error(process,50),[predicate-process_release/1,predicate-process_wait/2,predicate-process_wait/3|process_wait/3])
+
+```

tests/scryer/cli/unix/process.md

@@ -0,0 +1,14 @@
+```trycmd
+$ scryer-prolog -f --no-add-history -g 'use_module(library(process)), process_create("false", [], [process(P)]), process_wait(P, exit(1)), halt'
+
+```
+
+```trycmd
+$  scryer-prolog -f --no-add-history -g 'use_module(library(process)), use_module(library(format)), process_create("sh", [], [process(P), stdout(null), stdin(pipe(S))]), format(S, "exit 1~n", []), process_wait(P, exit(1)), halt'
+
+```
+
+```trycmd
+$  scryer-prolog -f --no-add-history -g 'use_module(library(process)), process_create("sh", ["-c", "sleep 5"], [process(P), stdout(null)]), process_kill(P), process_wait(P, killed(9)), halt'
+
+```

tests/scryer/cli/windows/process.md

@@ -0,0 +1,9 @@
+```trycmd
+$ scryer-prolog -f --no-add-history -g 'use_module(library(process)), process_create("cmd", ["/C", "exit", "1"], [process(P)]), process_wait(P, exit(1)), halt'
+
+```
+
+```trycmd
+$  scryer-prolog -f --no-add-history -g 'use_module(library(process)), use_module(library(format)), process_create("cmd", [], [process(P), stdout(null), stdin(pipe(S))]), format(S, "exit 1~n", []), process_wait(P, exit(1)), halt'
+
+```

tests/scryer/issues.rs

@@ -20,6 +20,12 @@ fn issue2588_load_html() {
     load_module_test("tests-pl/issue2588.pl", "[element(html,[],[element(head,[],[element(title,[],[[H,e,l,l,o,!]])]),element(body,[],[])])]");
 }
 
+#[test]
+#[cfg_attr(miri, ignore = "unsupported operation when isolation is enabled")]
+fn issue2949_load_html() {
+    load_module_test("tests-pl/issue2949.pl", "[doctype([h,t,m,l]),element(html,[],[element(head,[],[element(title,[],[[H,e,l,l,o,!]])]),element(body,[],[])])][doctype([h,t,m,l]),element(html,[],[element(head,[],[element(title,[],[[H,e,l,l,o,!]]),comment([ ,c,o,m,m,e,n,t, ])]),element(body,[],[])])][comment([]),element(html,[],[element(head,[],[]),element(body,[],[])])]");
+}
+
 // issue #2361
 #[serial]
 #[test]

tests/scryer/main.rs

@@ -19,9 +19,20 @@ mod src_tests;
     ignore = "miri isolation, unsupported operation: can't call foreign function"
 )]
 fn cli_tests() {
-    trycmd::TestCases::new()
+    let cases = trycmd::TestCases::new();
+    cases
         .default_bin_name("scryer-prolog")
         .case("tests/scryer/cli/issues/*.toml")
         .case("tests/scryer/cli/src_tests/*.toml")
         .case("tests/scryer/cli/src_tests/*.md");
+
+    #[cfg(windows)]
+    {
+        cases.case("tests/scryer/cli/windows/*.md");
+    }
+
+    #[cfg(unix)]
+    {
+        cases.case("tests/scryer/cli/unix/*.md");
+    }
 }