prep for debray allocation

Cargo.lock

@@ -1,6 +1,6 @@
 [root]
 name = "rusty-wam"
-version = "0.5.12"
+version = "0.5.7"
 dependencies = [
  "lalrpop 0.12.5 (registry+https://github.com/rust-lang/crates.io-index)",
  "lalrpop-util 0.12.5 (registry+https://github.com/rust-lang/crates.io-index)",

Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "rusty-wam"
-version = "0.5.12"
+version = "0.5.7"
 authors = ["Mark Thom"]
 
 build = "build.rs"

src/main.rs

@@ -200,7 +200,7 @@ mod tests {
 
         // test shallow cuts.
         submit(&mut wam, "memberchk(X, [X|_]) :- !.
-                          memberchk(X, [_|Xs]) :- !, memberchk(X, Xs).");
+                          memberchk(X, [_|Xs]) :- memberchk(X, Xs).");
 
         assert_eq!(submit(&mut wam, "?- memberchk(X, [a,b,c]).").failed_query(), false);
         assert_eq!(submit(&mut wam, "?- memberchk([X,X], [a,b,c,[d,e],[d,d]]).").failed_query(), false);

src/prolog/ast.rs

@@ -7,6 +7,11 @@ pub type Var = String;
 
 pub type Atom = String;
 
+#[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord)]
+pub enum GenContext {
+    Head, Mid(usize), Last(usize) // Mid/Last: chunk_num
+}
+
 pub enum PredicateClause {
     Fact(Term),
     Rule(Rule)
@@ -90,13 +95,6 @@ impl VarReg {
     pub fn is_temp(self) -> bool {
         !self.norm().is_perm()
     }
-
-    pub fn root_register(self) -> usize {
-        match self {
-            VarReg::ArgAndNorm(_, root) => root,
-            VarReg::Norm(root) => root.reg_num()
-        }
-    }
 }
 
 impl Default for VarReg {
@@ -124,7 +122,7 @@ pub enum TermOrCut {
     Term(Term)
 }
 
-impl TermOrCut {    
+impl TermOrCut {
     pub fn arity(&self) -> usize {
         match self {
             &TermOrCut::Term(ref term) => term.arity(),
@@ -147,6 +145,7 @@ impl Rule {
     }
 }
 
+#[derive(Clone, Copy)]
 pub enum TermRef<'a> {
     AnonVar(Level),
     Cons(Level, &'a Cell<RegType>, &'a Term, &'a Term),
@@ -155,6 +154,22 @@ pub enum TermRef<'a> {
     Var(Level, &'a Cell<VarReg>, &'a Var)
 }
 
+impl<'a> TermRef<'a> {
+    pub fn level(self) -> Level {
+        match self {
+            TermRef::AnonVar(lvl)
+          | TermRef::Cons(lvl, _, _, _)
+          | TermRef::Constant(lvl, _, _)
+          | TermRef::Clause(lvl, _, _, _)
+          | TermRef::Var(lvl, _, _) => lvl
+        }
+    }
+}
+
+pub enum TermOrCutRef<'a> {
+    Cut, Term(&'a Term)
+}
+
 pub enum ChoiceInstruction {
     RetryMeElse(usize),
     TrustMe,
@@ -410,6 +425,14 @@ impl Term {
         }
     }
 
+    pub fn is_callable(&self) -> bool {
+        match self {
+            &Term::Clause(_, _, _) | &Term::Constant(_, Constant::Atom(_)) =>
+                true,
+            _ => false
+        }
+    }
+
     pub fn subterms(&self) -> usize {
         match self {
             &Term::Clause(_, _, ref terms) => terms.len(),

src/prolog/indexing.rs

@@ -0,0 +1,247 @@
+use prolog::ast::*;
+
+use std::collections::{HashMap, VecDeque};
+use std::hash::Hash;
+
+#[derive(Clone, Copy)]
+enum IntIndex {
+    External(usize), Fail, Internal(usize)
+}
+
+pub struct CodeOffsets {
+    pub constants:  HashMap<Constant, ThirdLevelIndex>,
+    pub lists: ThirdLevelIndex,
+    pub structures: HashMap<(Atom, usize), ThirdLevelIndex>
+}
+
+impl CodeOffsets {
+    pub fn new() -> Self {
+        CodeOffsets {
+            constants: HashMap::new(),
+            lists: Vec::new(),
+            structures: HashMap::new()
+        }
+    }
+
+    fn cap_choice_seq_with_trust(prelude: &mut ThirdLevelIndex) {
+        prelude.last_mut().map(|instr| {
+            match instr {
+                &mut IndexedChoiceInstruction::Retry(i) =>
+                    *instr = IndexedChoiceInstruction::Trust(i),
+                _ => {}
+            };
+        });
+    }
+
+    fn add_index(is_first_index: bool, index: usize) -> IndexedChoiceInstruction {
+        if is_first_index {
+            IndexedChoiceInstruction::Try(index)
+        } else {
+            IndexedChoiceInstruction::Retry(index)
+        }
+    }
+
+    pub fn index_term(&mut self, first_arg: &Term, index: usize)
+    {
+        match first_arg {
+            &Term::Clause(_, ref name, ref terms) => {
+                let code = self.structures.entry((name.clone(), terms.len()))
+                               .or_insert(Vec::new());
+
+                let is_initial_index = code.is_empty();
+                code.push(Self::add_index(is_initial_index, index));
+            },
+            &Term::Cons(_, _, _) => {
+                let is_initial_index = self.lists.is_empty();
+                self.lists.push(Self::add_index(is_initial_index, index));
+            },
+            &Term::Constant(_, ref constant) => {
+                let code = self.constants.entry(constant.clone())
+                               .or_insert(Vec::new());
+
+                let is_initial_index = code.is_empty();
+                code.push(Self::add_index(is_initial_index, index));
+            },
+            _ => {}
+        };
+    }
+
+    fn second_level_index<Index>(indices: HashMap<Index, ThirdLevelIndex>,
+                                 prelude: &mut CodeDeque)
+                                 -> HashMap<Index, IntIndex>
+        where Index: Eq + Hash
+    {
+        let mut index_locs = HashMap::new();
+
+        for (key, mut code) in indices.into_iter() {
+            if code.len() > 1 {
+                index_locs.insert(key, IntIndex::Internal(prelude.len()));
+                Self::cap_choice_seq_with_trust(&mut code);
+                prelude.extend(code.into_iter().map(|code| Line::from(code)));
+            } else {
+                code.first().map(|i| {
+                    index_locs.insert(key, IntIndex::External(i.offset()));
+                });
+            }
+        }
+
+        index_locs
+    }
+
+    fn no_indices(&self) -> bool {
+        let no_constants = self.constants.is_empty();
+        let no_structures = self.structures.is_empty();
+        let no_lists = self.lists.is_empty();
+
+        no_constants && no_structures && no_lists
+    }
+
+    fn flatten_index<Index>(index: HashMap<Index, IntIndex>, len: usize)
+                            -> HashMap<Index, usize>
+        where Index: Eq + Hash
+    {
+        let mut flattened_index = HashMap::new();
+
+        for (key, int_index) in index.into_iter() {
+            match int_index {
+                IntIndex::External(offset) => {
+                    flattened_index.insert(key, offset + len + 1);
+                },
+                IntIndex::Internal(offset) => {
+                    flattened_index.insert(key, offset + 1);
+                },
+                _ => {}
+            };
+        }
+
+        flattened_index
+    }
+
+    fn switch_on_constant(con_ind: HashMap<Constant, ThirdLevelIndex>,
+                          prelude: &mut CodeDeque)
+                          -> IntIndex
+    {
+        let con_ind = Self::second_level_index(con_ind, prelude);
+
+        if con_ind.len() > 1 {
+            let index = Self::flatten_index(con_ind, prelude.len());
+            let instr = IndexingInstruction::SwitchOnConstant(index.len(), index);
+
+            prelude.push_front(Line::from(instr));
+
+            IntIndex::Internal(1)
+        } else {
+            con_ind.values().next()
+                   .map(|i| *i)
+                   .unwrap_or(IntIndex::Fail)
+        }
+    }
+
+    fn switch_on_list(mut lists: ThirdLevelIndex, prelude: &mut CodeDeque) -> IntIndex
+    {
+        if lists.len() > 1 {
+            Self::cap_choice_seq_with_trust(&mut lists);
+            prelude.extend(lists.into_iter().map(|i| Line::from(i)));
+            IntIndex::Internal(0)
+        } else {
+            lists.first()
+                 .map(|i| IntIndex::External(i.offset()))
+                 .unwrap_or(IntIndex::Fail)
+        }
+    }
+
+    fn switch_on_structure(str_ind: HashMap<(Atom, usize), ThirdLevelIndex>,
+                           prelude: &mut CodeDeque)
+                           -> IntIndex
+    {
+        let str_ind = Self::second_level_index(str_ind, prelude);
+
+        if str_ind.len() > 1 {
+            let index = Self::flatten_index(str_ind, prelude.len());
+            let instr = IndexingInstruction::SwitchOnStructure(index.len(), index);
+
+            prelude.push_front(Line::from(instr));
+
+            IntIndex::Internal(1)
+        } else {
+            str_ind.values().next()
+                   .map(|i| *i)
+                   .unwrap_or(IntIndex::Fail)
+        }
+    }
+
+
+    fn switch_on_str_offset_from(str_loc: IntIndex, prelude_len: usize, con_loc: IntIndex)
+                                 -> usize
+    {
+        match str_loc {
+            IntIndex::External(o) => o + prelude_len + 1,
+            IntIndex::Fail => 0,
+            IntIndex::Internal(_) => match con_loc {
+                IntIndex::Internal(_) => 2,
+                _ => 1
+            }
+        }
+    }
+
+    fn switch_on_con_offset_from(con_loc: IntIndex, prelude_len: usize) -> usize
+    {
+        match con_loc {
+            IntIndex::External(offset) => offset + prelude_len + 1,
+            IntIndex::Fail => 0,
+            IntIndex::Internal(offset) => offset,
+        }
+    }
+
+    fn switch_on_lst_offset_from(lst_loc: IntIndex, prelude_len: usize, lst_offset: usize)
+                                 -> usize
+    {
+        match lst_loc {
+            IntIndex::External(o) => o + prelude_len + 1,
+            IntIndex::Fail => 0,
+            IntIndex::Internal(_) => prelude_len - lst_offset + 1
+        }
+    }
+
+    pub fn add_indices(self, code: &mut Code, mut code_body: Code)
+    {
+        if self.no_indices() {
+            *code = code_body;
+            return;
+        }
+
+        let mut prelude = VecDeque::new();
+
+        let lst_loc = Self::switch_on_list(self.lists, &mut prelude);
+        let lst_offset = prelude.len();
+
+        let str_loc = Self::switch_on_structure(self.structures, &mut prelude);
+        let con_loc = Self::switch_on_constant(self.constants, &mut prelude);
+
+        let prelude_length = prelude.len();
+
+        for (index, line) in prelude.iter_mut().enumerate() {
+            match line {
+                  &mut Line::IndexedChoice(IndexedChoiceInstruction::Try(ref mut i))
+                | &mut Line::IndexedChoice(IndexedChoiceInstruction::Retry(ref mut i))
+                | &mut Line::IndexedChoice(IndexedChoiceInstruction::Trust(ref mut i)) =>
+                    *i += prelude_length - index,
+                _ => {}
+            }
+        }
+
+        let str_loc = Self::switch_on_str_offset_from(str_loc, prelude.len(), con_loc);
+        let con_loc = Self::switch_on_con_offset_from(con_loc, prelude.len());
+        let lst_loc = Self::switch_on_lst_offset_from(lst_loc, prelude.len(), lst_offset);
+
+        let switch_instr = IndexingInstruction::SwitchOnTerm(prelude.len() + 1,
+                                                             con_loc,
+                                                             lst_loc,
+                                                             str_loc);
+
+        prelude.push_front(Line::from(switch_instr));
+
+        *code = Vec::from(prelude);
+        code.append(&mut code_body);
+    }
+}

src/prolog/io.rs

@@ -121,11 +121,11 @@ impl fmt::Display for IndexedChoiceInstruction {
 
 impl fmt::Display for ChoiceInstruction {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
-        match self {            
+        match self {
             &ChoiceInstruction::TryMeElse(offset) =>
                 write!(f, "try_me_else {}", offset),
             &ChoiceInstruction::RetryMeElse(offset) =>
-                write!(f, "retry_me_else {}", offset),            
+                write!(f, "retry_me_else {}", offset),
             &ChoiceInstruction::TrustMe =>
                 write!(f, "trust_me")
         }
@@ -277,12 +277,12 @@ Each predicate must have the same name and arity.";
         },
         &Ok(TopLevel::Fact(ref fact)) => {
             let compiled_fact = cg.compile_fact(&fact);
-            wam.add_fact(fact, compiled_fact);
+            wam.add_fact(fact, compiled_fact);            
             EvalResult::EntrySuccess
         },
         &Ok(TopLevel::Rule(ref rule)) => {
             let compiled_rule = cg.compile_rule(&rule);
-            wam.add_rule(rule, compiled_rule);
+            wam.add_rule(rule, compiled_rule);            
             EvalResult::EntrySuccess
         },
         &Ok(TopLevel::Query(ref query)) => {

src/prolog/iterators.rs

@@ -2,6 +2,7 @@ use prolog::ast::*;
 
 use std::cell::Cell;
 use std::collections::VecDeque;
+use std::iter::*;
 use std::vec::Vec;
 
 enum IteratorState<'a> {
@@ -107,7 +108,7 @@ impl<'a> Iterator for QueryIterator<'a> {
                 IteratorState::InitialCons(lvl, cell, head, tail) => {
                     self.push_final_cons(lvl, cell, head, tail);
                     self.push_subterm(Level::Deep, tail);
-                    self.push_subterm(Level::Deep, head);                    
+                    self.push_subterm(Level::Deep, head);
                 },
                 IteratorState::FinalCons(lvl, cell, head, tail) =>
                     return Some(TermRef::Cons(lvl, cell, head, tail)),
@@ -207,3 +208,120 @@ impl Term {
         FactIterator::new(self)
     }
 }
+
+pub struct ChunkedIterator<'a>
+{
+    at_head: bool,
+    iter: Box<Iterator<Item=TermOrCutRef<'a>> + 'a>,
+    deep_cut_encountered: bool
+}
+
+impl<'a> ChunkedIterator<'a>
+{
+    pub fn from_term(term: &'a Term, at_head: bool) -> Self
+    {
+        let inner_iter: Box<Iterator<Item=TermOrCutRef<'a>>> =
+            Box::new(once(TermOrCutRef::Term(term)));
+
+        ChunkedIterator {
+            at_head: at_head,
+            iter: inner_iter,
+            deep_cut_encountered: false
+        }
+    }
+
+    pub fn from_term_sequence(terms: &'a Vec<TermOrCut>) -> Self
+    {
+        let iter = terms.iter().map(|c| {
+            match c {
+                &TermOrCut::Cut => TermOrCutRef::Cut,
+                &TermOrCut::Term(ref term) => TermOrCutRef::Term(term)
+            }
+        });
+
+        ChunkedIterator {
+            at_head: false,
+            iter: Box::new(iter),
+            deep_cut_encountered: false
+        }
+    }
+    
+    pub fn from_rule(rule: &'a Rule) -> Self
+    {
+        let &Rule { head: (ref p0, ref p1), ref clauses } = rule;
+        let iter = once(TermOrCutRef::Term(p0));
+
+        let inner_iter : Box<Iterator<Item=TermOrCutRef<'a>>> = match p1 {
+            &TermOrCut::Term(ref p1) => Box::new(once(TermOrCutRef::Term(p1))),
+            _ => Box::new(empty())
+        };
+
+        let iter = iter.chain(inner_iter.chain(clauses.iter().map(|c| {
+            match c {
+                &TermOrCut::Cut => TermOrCutRef::Cut,
+                &TermOrCut::Term(ref term) => TermOrCutRef::Term(term)
+            }
+        })));
+                              
+        ChunkedIterator {
+            at_head: true,
+            iter: Box::new(iter),
+            deep_cut_encountered: false
+        }
+    }
+
+    pub fn contains_deep_cut(&self) -> bool {
+        self.deep_cut_encountered
+    }
+
+    pub fn at_head(&self) -> bool {
+        self.at_head
+    }
+    
+    fn take_chunk(&mut self, term: TermOrCutRef<'a>) -> (usize, Vec<TermOrCutRef<'a>>)
+    {
+        let mut result = vec![term];
+        let mut arity = 0;
+
+        while let Some(term) = self.iter.next() {
+            match term {
+                TermOrCutRef::Term(inner_term) => {
+                    result.push(term);
+
+                    if inner_term.is_callable() {
+                        arity = inner_term.arity();
+                        break;
+                    }
+                },
+                _ => {
+                    result.push(term);
+                    self.deep_cut_encountered = true;                    
+                }
+            };
+        }
+
+        (arity, result)
+    }
+}
+
+impl<'a> Iterator for ChunkedIterator<'a>
+{
+    // the last term arity, and the reference.
+    type Item = (usize, Vec<TermOrCutRef<'a>>);
+
+    fn next(&mut self) -> Option<Self::Item> {
+        loop {
+            match self.iter.next() {
+                None => return None,
+                Some(TermOrCutRef::Term(term)) if self.at_head => {
+                    self.at_head = false;
+                    return Some(self.take_chunk(TermOrCutRef::Term(term)));
+                },
+                Some(TermOrCutRef::Term(term)) if term.is_callable() =>
+                    return Some((term.arity(), vec![TermOrCutRef::Term(term)])),
+                Some(term_or_cut_ref) =>
+                    return Some(self.take_chunk(term_or_cut_ref))
+            }
+        }
+    }
+}

src/prolog/machine.rs

@@ -251,8 +251,9 @@ impl Machine {
         }
 
         if succeeded {
-            for (var, vr) in cg.vars() {
+            for (var, var_status) in cg.vars() {
-                let addr = self.ms.registers[vr.root_register()].clone();
+                let r = var_status.as_reg_type().reg_num();
+                let addr = self.ms.registers[r].clone();                
                 heap_locs.insert((*var).clone(), addr);
             }
 

src/prolog/mod.rs

@@ -1,9 +1,13 @@
 pub mod and_stack;
 pub mod ast;
 pub mod codegen;
+pub mod fixtures;
 pub mod heapview;
+pub mod indexing;
 pub mod io;
 pub mod iterators;
+pub mod naive_allocator;
 pub mod prolog_parser;
 pub mod machine;
 pub mod or_stack;
+pub mod targets;

src/prolog/naive_allocator.rs

@@ -0,0 +1,163 @@
+use prolog::ast::*;
+use prolog::fixtures::*;
+
+use std::cell::Cell;
+use std::cmp::max;
+use std::collections::{BTreeSet, HashMap};
+
+pub struct TermMarker<'a> {    
+    pub bindings: HashMap<&'a Var, VarData>,
+    arg_c:    usize,
+    temp_c:   usize,
+    contents: HashMap<usize, &'a Var>,
+    in_use:   BTreeSet<usize>,
+}
+
+impl<'a> TermMarker<'a> {
+    pub fn new() -> TermMarker<'a> {
+        TermMarker {
+            arg_c:    1,
+            temp_c:   1,
+            bindings: HashMap::new(),
+            contents: HashMap::new(),
+            in_use: BTreeSet::new()
+        }
+    }
+
+    pub fn drain_var_data(&mut self, vs: VariableFixtures<'a>) -> VariableFixtures<'a>
+    {
+        let mut perm_vs = VariableFixtures::new();
+
+        for (var, (var_status, cells)) in vs.into_iter() {
+            match var_status {
+                VarStatus::Temp(chunk_num, tvd) => {
+                    self.bindings.insert(var, VarData::Temp(chunk_num, 0, tvd));
+                },
+                VarStatus::Perm(_) => {
+                    self.bindings.insert(var, VarData::Perm(0));
+                    perm_vs.insert(var, (var_status, cells));
+                }
+            };
+        }
+
+        perm_vs
+    }
+
+    fn get(&self, var: &'a Var) -> RegType {
+        self.bindings.get(var).unwrap().as_reg_type()
+    }
+
+    pub fn contains_var(&self, var: &'a Var) -> bool {
+        self.bindings.contains_key(var)
+    }
+
+    pub fn marked_var(&self, var: &'a Var) -> bool {
+        self.get(var).reg_num() != 0
+    }
+
+    fn record_register(&mut self, var: &'a Var, r: RegType) {
+        match self.bindings.get_mut(var).unwrap() {
+            &mut VarData::Temp(_, ref mut s, _) => *s = r.reg_num(),
+            &mut VarData::Perm(ref mut s) => *s = r.reg_num()
+        }
+    }
+
+    pub fn mark_non_var(&mut self, lvl: Level, cell: &Cell<RegType>) {
+        let reg_type = cell.get();
+
+        if reg_type.reg_num() == 0 {
+            match lvl {
+                Level::Deep if !reg_type.is_perm() => {
+                    let temp = self.temp_c;
+                    self.temp_c += 1;
+                    cell.set(RegType::Temp(temp));
+                },
+                Level::Shallow if !reg_type.is_perm() => {
+                    let arg = self.arg_c;
+                    self.arg_c += 1;
+                    cell.set(RegType::Temp(arg));
+                },
+                _ => {}
+            };
+        }
+    }
+
+    pub fn mark_old_var(&mut self, lvl: Level, var: &'a Var) -> VarReg
+    {
+        let inner_reg = self.get(var);
+
+        match lvl {
+            Level::Deep => VarReg::Norm(inner_reg),
+            Level::Shallow => {
+                let reg = VarReg::ArgAndNorm(inner_reg, self.arg_c);
+                self.arg_c += 1;
+                reg
+            }
+        }
+    }
+
+    pub fn mark_new_var(&mut self, lvl: Level, var: &'a Var, reg: RegType) -> VarReg
+    {
+        let inner_reg = if !reg.is_perm() {
+            let temp = self.temp_c;
+            self.temp_c += 1;
+            RegType::Temp(temp)
+        } else {
+            reg
+        };
+
+        let reg = match lvl {
+            Level::Deep => VarReg::Norm(inner_reg),
+            Level::Shallow => {
+                let reg = VarReg::ArgAndNorm(inner_reg, self.arg_c);
+                self.arg_c += 1;
+                reg
+            }
+        };
+
+        self.record_register(var, inner_reg);
+        reg
+    }
+
+    pub fn mark_anon_var(&mut self, lvl: Level) -> VarReg {
+        let inner_reg = {
+            let temp = self.temp_c;
+            self.temp_c += 1;
+            RegType::Temp(temp)
+        };
+
+        match lvl {
+            Level::Deep => VarReg::Norm(inner_reg),
+            Level::Shallow => {
+                let reg = VarReg::ArgAndNorm(inner_reg, self.arg_c);
+                self.arg_c += 1;
+                reg
+            }
+        }
+    }
+
+    pub fn advance_arg(&mut self) {
+        self.arg_c += 1;
+    }
+
+    pub fn advance_at_head(&mut self, term: &'a Term) {
+        self.arg_c  = 1;
+        self.temp_c = max(term.subterms() + 1, self.temp_c);
+    }
+
+    pub fn advance(&mut self, term: &'a Term) {
+        self.arg_c  = 1;
+        self.temp_c = term.subterms() + 1;
+    }
+
+    pub fn reset(&mut self) {
+        self.bindings.clear();
+        self.contents.clear();
+        self.in_use.clear();
+    }
+
+    pub fn reset_contents(&mut self) {
+        self.contents.clear();
+        self.in_use.clear();
+    }
+}

src/prolog/targets.rs

@@ -0,0 +1,119 @@
+use prolog::ast::*;
+use prolog::iterators::*;
+
+pub trait CompilationTarget<'a> {
+    type Iterator : Iterator<Item=TermRef<'a>>;
+
+    fn iter(&'a Term) -> Self::Iterator;
+
+    fn to_constant(Level, Constant, RegType) -> Self;
+    fn to_list(Level, RegType) -> Self;
+    fn to_structure(Level, Atom, usize, RegType) -> Self;
+    fn to_void(usize) -> Self;
+
+    fn constant_subterm(Constant) -> Self;
+
+    fn argument_to_variable(RegType, usize) -> Self;
+    fn argument_to_value(RegType, usize) -> Self;
+
+    fn subterm_to_variable(RegType) -> Self;
+    fn subterm_to_value(RegType) -> Self;
+
+    fn clause_arg_to_instr(RegType) -> Self;
+}
+
+impl<'a> CompilationTarget<'a> for FactInstruction {
+    type Iterator = FactIterator<'a>;
+
+    fn iter(term: &'a Term) -> Self::Iterator {
+        term.breadth_first_iter()
+    }
+
+    fn to_constant(lvl: Level, constant: Constant, reg: RegType) -> Self {
+        FactInstruction::GetConstant(lvl, constant, reg)
+    }
+
+    fn to_structure(lvl: Level, atom: Atom, arity: usize, reg: RegType) -> Self {
+        FactInstruction::GetStructure(lvl, atom, arity, reg)
+    }
+
+    fn to_list(lvl: Level, reg: RegType) -> Self {
+        FactInstruction::GetList(lvl, reg)
+    }
+
+    fn to_void(subterms: usize) -> Self {
+        FactInstruction::UnifyVoid(subterms)
+    }
+
+    fn constant_subterm(constant: Constant) -> Self {
+        FactInstruction::UnifyConstant(constant)
+    }
+
+    fn argument_to_variable(arg: RegType, val: usize) -> Self {
+        FactInstruction::GetVariable(arg, val)
+    }
+
+    fn argument_to_value(arg: RegType, val: usize) -> Self {
+        FactInstruction::GetValue(arg, val)
+    }
+
+    fn subterm_to_variable(val: RegType) -> Self {
+        FactInstruction::UnifyVariable(val)
+    }
+
+    fn subterm_to_value(val: RegType) -> Self {
+        FactInstruction::UnifyValue(val)
+    }
+
+    fn clause_arg_to_instr(val: RegType) -> Self {
+        FactInstruction::UnifyVariable(val)
+    }
+}
+
+impl<'a> CompilationTarget<'a> for QueryInstruction {
+    type Iterator = QueryIterator<'a>;
+
+    fn iter(term: &'a Term) -> Self::Iterator {
+        term.post_order_iter()
+    }
+
+    fn to_structure(lvl: Level, atom: Atom, arity: usize, reg: RegType) -> Self {
+        QueryInstruction::PutStructure(lvl, atom, arity, reg)
+    }
+
+    fn to_constant(lvl: Level, constant: Constant, reg: RegType) -> Self {
+        QueryInstruction::PutConstant(lvl, constant, reg)
+    }
+
+    fn to_list(lvl: Level, reg: RegType) -> Self {
+        QueryInstruction::PutList(lvl, reg)
+    }
+
+    fn to_void(subterms: usize) -> Self {
+        QueryInstruction::SetVoid(subterms)
+    }
+
+    fn constant_subterm(constant: Constant) -> Self {
+        QueryInstruction::SetConstant(constant)
+    }
+
+    fn argument_to_variable(arg: RegType, val: usize) -> Self {
+        QueryInstruction::PutVariable(arg, val)
+    }
+
+    fn argument_to_value(arg: RegType, val: usize) -> Self {
+        QueryInstruction::PutValue(arg, val)
+    }
+
+    fn subterm_to_variable(val: RegType) -> Self {
+        QueryInstruction::SetVariable(val)
+    }
+
+    fn subterm_to_value(val: RegType) -> Self {
+        QueryInstruction::SetValue(val)
+    }
+
+    fn clause_arg_to_instr(val: RegType) -> Self {
+        QueryInstruction::SetValue(val)
+    }
+}