optimized up to section 5.11

src/main.rs

@@ -239,6 +239,154 @@ mod tests {
         assert_eq!(submit(&mut wam, "?- member([X, Y, Y], [a, [b, c], [b, b], [Z, x], [d, f]]).").failed_query(), true);
         assert_eq!(submit(&mut wam, "?- member([X, Y, Z], [a, [b, c], [b, b], [Z, x], [d, f]]).").failed_query(), true);
     }
+
+    #[test]
+    fn test_queries_on_indexed_predicates() {
+        let mut wam = Machine::new();
+
+        submit(&mut wam, "p(a) :- a.
+                          p(b) :- b, f(X).
+                          p(c) :- c, g(X).
+                          p(f(a)) :- a.
+                          p(g(b, c)) :- b.
+                          p(g(b)) :- b.
+                          p([a|b]) :- a.
+                          p([]).
+                          p(X) :- x.
+                          p([c, d, e]).");
+
+        assert_eq!(submit(&mut wam, "?- p(a).").failed_query(), true);
+        assert_eq!(submit(&mut wam, "?- p(b).").failed_query(), true);
+        assert_eq!(submit(&mut wam, "?- p(c).").failed_query(), true);
+        assert_eq!(submit(&mut wam, "?- p(f(a)).").failed_query(), true);
+        assert_eq!(submit(&mut wam, "?- p(g(b, X)).").failed_query(), true);
+        assert_eq!(submit(&mut wam, "?- p(g(Y, X)).").failed_query(), true);
+        assert_eq!(submit(&mut wam, "?- p(g(Y, c)).").failed_query(), true);
+        assert_eq!(submit(&mut wam, "?- p(g(b)).").failed_query(), true);
+        assert_eq!(submit(&mut wam, "?- p([]).").failed_query(), false);
+        assert_eq!(submit(&mut wam, "?- p([c, d, e]).").failed_query(), false);
+        assert_eq!(submit(&mut wam, "?- p([c, d | X]).").failed_query(), false);
+        assert_eq!(submit(&mut wam, "?- p([c|X]).").failed_query(), false);
+        assert_eq!(submit(&mut wam, "?- p([Y|X]).").failed_query(), false);
+        assert_eq!(submit(&mut wam, "?- p([Y|[d|Xs]]).").failed_query(), false);        
+
+        submit(&mut wam, "a.");
+        
+        assert_eq!(submit(&mut wam, "?- p(a).").failed_query(), false);
+        assert_eq!(submit(&mut wam, "?- p(b).").failed_query(), true);
+        assert_eq!(submit(&mut wam, "?- p(c).").failed_query(), true);
+        assert_eq!(submit(&mut wam, "?- p(f(a)).").failed_query(), false);
+        assert_eq!(submit(&mut wam, "?- p(g(b, X)).").failed_query(), true);
+        assert_eq!(submit(&mut wam, "?- p(g(Y, X)).").failed_query(), true);
+        assert_eq!(submit(&mut wam, "?- p(g(Y, c)).").failed_query(), true);
+        assert_eq!(submit(&mut wam, "?- p(g(b)).").failed_query(), true);
+        assert_eq!(submit(&mut wam, "?- p([]).").failed_query(), false);
+        assert_eq!(submit(&mut wam, "?- p([c, d, e]).").failed_query(), false);
+        assert_eq!(submit(&mut wam, "?- p([c, d | X]).").failed_query(), false);
+        assert_eq!(submit(&mut wam, "?- p([c|X]).").failed_query(), false);
+        assert_eq!(submit(&mut wam, "?- p([Y|X]).").failed_query(), false);
+        assert_eq!(submit(&mut wam, "?- p([Y|[d|Xs]]).").failed_query(), false);        
+
+        submit(&mut wam, "b.");
+        submit(&mut wam, "f(x).");
+        
+        assert_eq!(submit(&mut wam, "?- p(a).").failed_query(), false);
+        assert_eq!(submit(&mut wam, "?- p(b).").failed_query(), false);
+        assert_eq!(submit(&mut wam, "?- p(c).").failed_query(), true);
+        assert_eq!(submit(&mut wam, "?- p(f(a)).").failed_query(), false);
+        assert_eq!(submit(&mut wam, "?- p(g(b, X)).").failed_query(), false);
+        assert_eq!(submit(&mut wam, "?- p(g(Y, X)).").failed_query(), false);
+        assert_eq!(submit(&mut wam, "?- p(g(Y, c)).").failed_query(), false);
+        assert_eq!(submit(&mut wam, "?- p(g(b)).").failed_query(), false);
+        assert_eq!(submit(&mut wam, "?- p([]).").failed_query(), false);
+        assert_eq!(submit(&mut wam, "?- p([c, d, e]).").failed_query(), false);
+        assert_eq!(submit(&mut wam, "?- p([c, d | X]).").failed_query(), false);
+        assert_eq!(submit(&mut wam, "?- p([c|X]).").failed_query(), false);
+        assert_eq!(submit(&mut wam, "?- p([Y|X]).").failed_query(), false);
+        assert_eq!(submit(&mut wam, "?- p([Y|[d|Xs]]).").failed_query(), false);
+
+        submit(&mut wam, "c.");
+        submit(&mut wam, "g(X).");
+
+        assert_eq!(submit(&mut wam, "?- p(a).").failed_query(), false);
+        assert_eq!(submit(&mut wam, "?- p(b).").failed_query(), false);
+        assert_eq!(submit(&mut wam, "?- p(c).").failed_query(), false);
+        assert_eq!(submit(&mut wam, "?- p(f(a)).").failed_query(), false);
+        assert_eq!(submit(&mut wam, "?- p(g(b, X)).").failed_query(), false);
+        assert_eq!(submit(&mut wam, "?- p(g(Y, X)).").failed_query(), false);
+        assert_eq!(submit(&mut wam, "?- p(g(Y, c)).").failed_query(), false);
+        assert_eq!(submit(&mut wam, "?- p(g(b)).").failed_query(), false);
+        assert_eq!(submit(&mut wam, "?- p([]).").failed_query(), false);
+        assert_eq!(submit(&mut wam, "?- p([c, d, e]).").failed_query(), false);
+        assert_eq!(submit(&mut wam, "?- p([c, d | X]).").failed_query(), false);
+        assert_eq!(submit(&mut wam, "?- p([c|X]).").failed_query(), false);
+        assert_eq!(submit(&mut wam, "?- p([Y|X]).").failed_query(), false);
+        assert_eq!(submit(&mut wam, "?- p([Y|[d|Xs]]).").failed_query(), false);
+        assert_eq!(submit(&mut wam, "?- p(blah).").failed_query(), true);
+
+        submit(&mut wam, "x.");
+       
+        assert_eq!(submit(&mut wam, "?- p(a).").failed_query(), false);
+        assert_eq!(submit(&mut wam, "?- p(b).").failed_query(), false);
+        assert_eq!(submit(&mut wam, "?- p(c).").failed_query(), false);
+        assert_eq!(submit(&mut wam, "?- p(f(a)).").failed_query(), false);
+        assert_eq!(submit(&mut wam, "?- p(g(b, X)).").failed_query(), false);
+        assert_eq!(submit(&mut wam, "?- p(g(Y, X)).").failed_query(), false);
+        assert_eq!(submit(&mut wam, "?- p(g(Y, c)).").failed_query(), false);
+        assert_eq!(submit(&mut wam, "?- p(g(b)).").failed_query(), false);
+        assert_eq!(submit(&mut wam, "?- p([]).").failed_query(), false);
+        assert_eq!(submit(&mut wam, "?- p([c, d, e]).").failed_query(), false);
+        assert_eq!(submit(&mut wam, "?- p([c, d | X]).").failed_query(), false);
+        assert_eq!(submit(&mut wam, "?- p([c|X]).").failed_query(), false);
+        assert_eq!(submit(&mut wam, "?- p([Y|X]).").failed_query(), false);
+        assert_eq!(submit(&mut wam, "?- p([Y|[d|Xs]]).").failed_query(), false);
+        assert_eq!(submit(&mut wam, "?- p(blah).").failed_query(), false);
+
+        submit(&mut wam, "call(or(X, Y)) :- call(X).
+                          call(trace) :- trace.
+                          call(or(X, Y)) :- call(Y).
+                          call(notrace) :- notrace.
+                          call(nl) :- nl.
+                          call(X) :- builtin(X).
+                          call(X) :- extern(X).
+                          call(call(X)) :- call(X).
+                          call(repeat).
+                          call(repeat) :- call(repeat).
+                          call(true).");
+
+        assert_eq!(submit(&mut wam, "?- call(repeat).").failed_query(), false);
+        assert_eq!(submit(&mut wam, "?- call(true).").failed_query(), false);
+        assert_eq!(submit(&mut wam, "?- call(call(repeat)).").failed_query(), false);
+        assert_eq!(submit(&mut wam, "?- call(call(true)).").failed_query(), false);
+        assert_eq!(submit(&mut wam, "?- call(notrace).").failed_query(), true);
+        assert_eq!(submit(&mut wam, "?- call(nl).").failed_query(), true);
+        assert_eq!(submit(&mut wam, "?- call(builtin(X)).").failed_query(), true);
+        assert_eq!(submit(&mut wam, "?- call(extern(X)).").failed_query(), true);
+        
+        submit(&mut wam, "notrace.");
+        submit(&mut wam, "nl.");
+        
+        assert_eq!(submit(&mut wam, "?- call(repeat).").failed_query(), false);
+        assert_eq!(submit(&mut wam, "?- call(true).").failed_query(), false);
+        assert_eq!(submit(&mut wam, "?- call(call(repeat)).").failed_query(), false);
+        assert_eq!(submit(&mut wam, "?- call(call(true)).").failed_query(), false);
+        assert_eq!(submit(&mut wam, "?- call(notrace).").failed_query(), false);
+        assert_eq!(submit(&mut wam, "?- call(nl).").failed_query(), false);
+        assert_eq!(submit(&mut wam, "?- call(builtin(X)).").failed_query(), true);
+        assert_eq!(submit(&mut wam, "?- call(extern(X)).").failed_query(), true);        
+        
+        submit(&mut wam, "builtin(X).");
+        submit(&mut wam, "extern(x).");
+
+        assert_eq!(submit(&mut wam, "?- call(repeat).").failed_query(), false);
+        assert_eq!(submit(&mut wam, "?- call(true).").failed_query(), false);
+        assert_eq!(submit(&mut wam, "?- call(call(repeat)).").failed_query(), false);
+        assert_eq!(submit(&mut wam, "?- call(call(true)).").failed_query(), false);
+        assert_eq!(submit(&mut wam, "?- call(notrace).").failed_query(), false);
+        assert_eq!(submit(&mut wam, "?- call(nl).").failed_query(), false);
+        assert_eq!(submit(&mut wam, "?- call(builtin(X)).").failed_query(), false);
+        assert_eq!(submit(&mut wam, "?- call(extern(X)).").failed_query(), false);
+    }
 }
 
 fn prolog_repl() {

src/prolog/ast.rs

@@ -1,6 +1,5 @@
 use std::cell::Cell;
-use std::cmp::Ordering;
-use std::collections::HashMap;
+use std::collections::{HashMap, VecDeque};
 use std::ops::{Add, AddAssign};
 use std::vec::Vec;
 
@@ -21,6 +20,13 @@ impl PredicateClause {
         }
     }
 
+    pub fn first_arg(&self) -> Option<&Term> {
+        match self {
+            &PredicateClause::Fact(ref t) => t.first_arg(),
+            &PredicateClause::Rule(ref rule) => rule.head.0.first_arg()
+        }
+    }
+
     pub fn arity(&self) -> usize {
         match self {
             &PredicateClause::Fact(ref t) => t.arity(),
@@ -99,7 +105,7 @@ impl Default for VarReg {
     }
 }
 
-#[derive(Clone, PartialEq)]
+#[derive(Clone, Hash, PartialEq, Eq)]
 pub enum Constant {
     Atom(Atom),
     EmptyList
@@ -118,7 +124,7 @@ pub struct Rule {
     pub clauses: Vec<Term>
 }
 
-impl Rule {
+impl Rule {    
     pub fn last_clause(&self) -> &Term {
         match self.clauses.last() {
             None => &self.head.1,
@@ -135,6 +141,54 @@ pub enum TermRef<'a> {
     Var(Level, &'a Cell<VarReg>, &'a Var)
 }
 
+pub enum ChoiceInstruction {    
+    RetryMeElse(usize),        
+    TrustMe,    
+    TryMeElse(usize)
+}
+
+pub enum IndexedChoiceInstruction {
+    Retry(usize),
+    Trust(usize),
+    Try(usize)
+}
+
+impl From<IndexedChoiceInstruction> for Line {
+    fn from(i: IndexedChoiceInstruction) -> Self {
+        Line::IndexedChoice(i)
+    }
+}
+
+impl IndexedChoiceInstruction {
+    pub fn offset(&self) -> usize {
+        match self {
+            &IndexedChoiceInstruction::Retry(offset) => offset,
+            &IndexedChoiceInstruction::Trust(offset) => offset,
+            &IndexedChoiceInstruction::Try(offset)   => offset
+        }
+    }
+}
+
+pub enum ControlInstruction {
+    Allocate(usize),
+    Call(Atom, usize, usize),
+    Deallocate,
+    Execute(Atom, usize),
+    Proceed
+}
+
+pub enum IndexingInstruction {
+    SwitchOnTerm(usize, usize, usize, usize),
+    SwitchOnConstant(usize, HashMap<Constant, usize>),
+    SwitchOnStructure(usize, HashMap<(Atom, usize), usize>)
+}
+
+impl From<IndexingInstruction> for Line {
+    fn from(i: IndexingInstruction) -> Self {
+        Line::Indexing(i)
+    }
+}
+
 pub enum FactInstruction {
     GetConstant(Level, Constant, RegType),
     GetList(Level, RegType),
@@ -162,20 +216,6 @@ pub enum QueryInstruction {
     SetVoid(usize)
 }
 
-pub enum ChoiceInstruction {
-    RetryMeElse(usize),
-    TrustMe,
-    TryMeElse(usize)
-}
-
-pub enum ControlInstruction {
-    Allocate(usize),
-    Call(Atom, usize, usize),
-    Deallocate,
-    Execute(Atom, usize),
-    Proceed
-}
-
 pub type CompiledFact = Vec<FactInstruction>;
 
 pub type CompiledQuery = Vec<QueryInstruction>;
@@ -184,6 +224,8 @@ pub enum Line {
     Choice(ChoiceInstruction),
     Control(ControlInstruction),
     Fact(CompiledFact),
+    Indexing(IndexingInstruction),
+    IndexedChoice(IndexedChoiceInstruction),
     Query(CompiledQuery)
 }
 
@@ -198,8 +240,11 @@ impl<'a> From<&'a Line> for LineOrCodeOffset<'a> {
     }
 }
 
+pub type ThirdLevelIndex = Vec<IndexedChoiceInstruction>;
+
 pub type Code = Vec<Line>;
 
+pub type CodeDeque = VecDeque<Line>;
 
 #[derive(Clone, PartialEq)]
 pub enum Addr {
@@ -287,26 +332,6 @@ impl HeapCellValue {
     }
 }
 
-impl PartialOrd for Ref {
-    fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
-        match (*self, *other) {
-            (Ref::HeapCell(hc1), Ref::HeapCell(hc2)) =>
-                Some(hc1.cmp(&hc2)),
-            (Ref::HeapCell(_), _) =>
-                Some(Ordering::Less),
-            (Ref::StackCell(fr1, sc1), Ref::StackCell(fr2, sc2)) =>
-                if fr1 < fr2 {
-                    Some(Ordering::Less)
-                } else if fr1 == fr2 {
-                    Some(sc1.cmp(&sc2))
-                } else {
-                    Some(Ordering::Greater)
-                },
-            _ => Some(Ordering::Greater)
-        }
-    }
-}
-
 #[derive(Clone, Copy)]
 pub enum CodePtr {
     DirEntry(usize),
@@ -344,6 +369,14 @@ pub type Heap = Vec<HeapCellValue>;
 pub type Registers = Vec<Addr>;
 
 impl Term {
+    pub fn first_arg(&self) -> Option<&Term> {
+        match self {
+            &Term::Clause(_, _, ref terms) =>
+                terms.first().map(|bt| bt.as_ref()),
+            _ => None                
+        }
+    }
+    
     pub fn is_clause(&self) -> bool {
         if let &Term::Clause(_, _, _) = self {
             true
@@ -362,7 +395,7 @@ impl Term {
     pub fn name(&self) -> Option<&Atom> {
         match self {
             &Term::Constant(_, Constant::Atom(ref atom))
-            | &Term::Clause(_, ref atom, _) => Some(atom),
+          | &Term::Clause(_, ref atom, _) => Some(atom),
             _ => None
         }
     }

src/prolog/codegen.rs

@@ -3,7 +3,8 @@ use prolog::iterators::{FactIterator, QueryIterator};
 
 use std::cell::Cell;
 use std::cmp::max;
-use std::collections::HashMap;
+use std::collections::{HashMap, VecDeque};
+use std::hash::Hash;
 use std::vec::Vec;
 
 trait CompilationTarget<'a> {
@@ -244,6 +245,239 @@ impl<'a> TermMarker<'a> {
     }
 }
 
+#[derive(Clone, Copy)]
+enum IntIndex {
+    External(usize), Fail, Internal(usize)
+}
+
+impl Into<usize> for IntIndex {
+    fn into(self) -> usize {
+        match self {
+            IntIndex::Internal(i) => i,
+            _ => 0
+        }
+    }
+}
+
+struct CodeOffsets {
+    constants:  HashMap<Constant, ThirdLevelIndex>,
+    lists: ThirdLevelIndex,
+    structures: HashMap<(Atom, usize), ThirdLevelIndex>
+}
+
+impl CodeOffsets {
+    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)
+        }
+    }
+
+    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 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_step = Self::switch_on_list(self.lists, &mut prelude);
+        let lst_offset = prelude.len();
+
+        let str_step = Self::switch_on_structure(self.structures, &mut prelude);
+        let con_step = 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_step = match str_step {
+            IntIndex::External(o) => o + prelude.len() + 1,
+            IntIndex::Fail => 0,
+            IntIndex::Internal(_) => match con_step {
+                IntIndex::Internal(_) => 2,
+                _ => 1
+            }
+        };
+        let con_step = match con_step {
+            IntIndex::External(offset) => offset + prelude.len() + 1,
+            IntIndex::Fail => 0,
+            IntIndex::Internal(offset) => offset,
+        };
+        let lst_step = match lst_step {
+            IntIndex::External(o) => o + prelude.len() + 1,
+            IntIndex::Fail => 0,
+            IntIndex::Internal(_) => prelude.len() - lst_offset + 1
+        };
+
+        let switch_instr = IndexingInstruction::SwitchOnTerm(prelude.len() + 1,
+                                                             con_step,
+                                                             lst_step,
+                                                             str_step);
+
+        prelude.push_front(Line::from(switch_instr));
+
+        *code = Vec::from(prelude);
+        code.append(&mut code_body);
+    }
+}
+
 #[derive(Copy, Clone)]
 enum VarStatus {
     New, Old, Permanent(usize)
@@ -643,7 +877,7 @@ impl<'a> CodeGenerator<'a> {
         Self::add_conditional_call(&mut body, p1, perm_vars);
 
         body = clauses.iter().enumerate()
-            .map(|(i, ref term)| {
+            .map(|(i, term)| {
                 let num_vars = Self::vars_above_threshold(&vs, i+1);
                 self.compile_internal_query(term, num_vars)
             })
@@ -705,13 +939,13 @@ impl<'a> CodeGenerator<'a> {
         self.update_var_count(term.breadth_first_iter());
 
         let mut code = Vec::new();
-        
+
         if term.is_clause() {
-            let mut compiled_fact = self.compile_target(term, false);            
+            let mut compiled_fact = self.compile_target(term, false);
             Self::mark_unsafe_fact_vars(&mut compiled_fact, self.vars());
             code.push(Line::Fact(compiled_fact));
         }
-        
+
         let proceed = Line::Control(ControlInstruction::Proceed);
 
         code.push(proceed);
@@ -725,11 +959,11 @@ impl<'a> CodeGenerator<'a> {
 
         let mut code = Vec::new();
 
-        if term.is_clause() {                
+        if term.is_clause() {
             let compiled_query = Line::Query(self.compile_target(term, false));
             code.push(compiled_query);
         }
-        
+
         Self::add_conditional_call(&mut code, term, index);
 
         code
@@ -741,19 +975,45 @@ impl<'a> CodeGenerator<'a> {
 
         let mut code = Vec::new();
 
-        if term.is_clause() {                
+        if term.is_clause() {
             let compiled_query = Line::Query(self.compile_target(term, false));
             code.push(compiled_query);
         }
-        
+
         Self::add_conditional_call(&mut code, term, 0);
 
         code
     }
 
-    pub fn compile_predicate(&mut self, clauses: &'a Vec<PredicateClause>) -> Code
+    fn split_predicate(clauses: &Vec<PredicateClause>) -> Vec<(usize, usize)>
     {
-        let mut code = Vec::new();
+        let mut subseqs = Vec::new();
+        let mut left_index = 0;
+
+        for (right_index, clause) in clauses.iter().enumerate() {
+            if let Some(&Term::Var(_, _)) = clause.first_arg() {
+                if left_index < right_index {
+                    subseqs.push((left_index, right_index));
+                }
+
+                subseqs.push((right_index, right_index + 1));
+                left_index = right_index + 1;
+            }
+        }
+
+        if left_index < clauses.len() {
+            subseqs.push((left_index, clauses.len()));
+        }
+
+        subseqs
+    }
+
+    fn compile_pred_subseq(&mut self, clauses: &'a [PredicateClause]) -> Code
+    {
+        let mut code_body = Vec::new();
+        let mut code_offsets = CodeOffsets::new();
+
+        let multi_clause = clauses.len() > 1;
 
         for (i, clause) in clauses.iter().enumerate() {
             self.marker.reset();
@@ -765,14 +1025,50 @@ impl<'a> CodeGenerator<'a> {
                     self.compile_rule(rule)
             };
 
-            let choice = match i {
-                0 => ChoiceInstruction::TryMeElse(clause_code.len() + 1),
-                _ if i == clauses.len() - 1 => ChoiceInstruction::TrustMe,
-                _ => ChoiceInstruction::RetryMeElse(clause_code.len() + 1)
-            };
+            if multi_clause {
+                let choice = match i {
+                    0 => ChoiceInstruction::TryMeElse(clause_code.len() + 1),
+                    _ if i == clauses.len() - 1 => ChoiceInstruction::TrustMe,
+                    _ => ChoiceInstruction::RetryMeElse(clause_code.len() + 1)
+                };
 
-            code.push(Line::Choice(choice));
-            code.append(&mut clause_code);
+                code_body.push(Line::Choice(choice));
+            }
+
+            clause.first_arg().map(|arg| {
+                let index = code_body.len();
+                code_offsets.index_term(arg, index);
+            });
+
+            code_body.append(&mut clause_code);
+        }
+
+        let mut code = Vec::new();
+
+        code_offsets.add_indices(&mut code, code_body);
+        code
+    }
+
+    pub fn compile_predicate(&mut self, clauses: &'a Vec<PredicateClause>) -> Code
+    {
+        let mut code = Vec::new();
+        let split_pred = Self::split_predicate(clauses);
+        let multi_seq  = split_pred.len() > 1;
+
+        for &(l, r) in split_pred.iter() {
+            let mut code_segment = self.compile_pred_subseq(&clauses[l .. r]);
+
+            if multi_seq {
+                let choice = match l {
+                    0 => ChoiceInstruction::TryMeElse(code_segment.len() + 1),
+                    _ if r == clauses.len() => ChoiceInstruction::TrustMe,
+                    _ => ChoiceInstruction::RetryMeElse(code_segment.len() + 1)
+                };
+
+                code.push(Line::Choice(choice));
+            }
+
+            code.append(&mut code_segment);
         }
 
         code

src/prolog/io.rs

@@ -106,19 +106,45 @@ impl fmt::Display for ControlInstruction {
     }
 }
 
-impl fmt::Display for ChoiceInstruction {
+impl fmt::Display for IndexedChoiceInstruction {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         match self {
+            &IndexedChoiceInstruction::Try(offset) =>
+                write!(f, "try {}", offset),
+            &IndexedChoiceInstruction::Retry(offset) =>
+                write!(f, "retry {}", offset),
+            &IndexedChoiceInstruction::Trust(offset) =>
+                write!(f, "trust {}", offset)
+        }
+    }
+}
+
+impl fmt::Display for ChoiceInstruction {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        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")
         }
     }
 }
 
+impl fmt::Display for IndexingInstruction {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        match self {
+            &IndexingInstruction::SwitchOnTerm(v, c, l, s) =>
+                write!(f, "switch_on_term {}, {}, {}, {}", v, c, l, s),
+            &IndexingInstruction::SwitchOnConstant(num_cs, _) =>
+                write!(f, "switch_on_constant {}", num_cs),
+            &IndexingInstruction::SwitchOnStructure(num_ss, _) =>
+                write!(f, "switch_on_structure {}", num_ss)
+        }
+    }
+}
+
 impl fmt::Display for Level {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         match self {
@@ -176,6 +202,10 @@ pub fn print_code(code: &Code) {
                 println!("{}", choice),
             &Line::Control(ref control) =>
                 println!("{}", control),
+            &Line::IndexedChoice(ref choice) =>
+                println!("{}", choice),
+            &Line::Indexing(ref indexing) =>
+                println!("{}", indexing),
             &Line::Query(ref query) =>
                 for query_instr in query {
                     println!("{}", query_instr);
@@ -218,7 +248,7 @@ pub fn eval(wam: &mut Machine, buffer: &str) -> EvalResult
     match &result {
         &Ok(TopLevel::Predicate(ref clauses)) => {
             if is_consistent(clauses) {
-                let compiled_pred = cg.compile_predicate(clauses);                
+                let compiled_pred = cg.compile_predicate(clauses);
                 wam.add_predicate(clauses, compiled_pred);
 
                 EvalResult::EntrySuccess
@@ -231,17 +261,17 @@ Each predicate must have the same name and arity.";
             }
         },
         &Ok(TopLevel::Fact(ref fact)) => {
-            let compiled_fact = cg.compile_fact(&fact);            
+            let compiled_fact = cg.compile_fact(&fact);
             wam.add_fact(fact, compiled_fact);
             EvalResult::EntrySuccess
         },
         &Ok(TopLevel::Rule(ref rule)) => {
-            let compiled_rule = cg.compile_rule(&rule);            
+            let compiled_rule = cg.compile_rule(&rule);
             wam.add_rule(rule, compiled_rule);
             EvalResult::EntrySuccess
         },
         &Ok(TopLevel::Query(ref query)) => {
-            let compiled_query = cg.compile_query(&query);            
+            let compiled_query = cg.compile_query(&query);
             wam.run_query(compiled_query, &cg)
         },
         &Err(_) => {

src/prolog/iterators.rs

@@ -106,8 +106,8 @@ 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, head);
                     self.push_subterm(Level::Deep, tail);
+                    self.push_subterm(Level::Deep, head);                    
                 },
                 IteratorState::FinalCons(lvl, cell, head, tail) =>
                     return Some(TermRef::Cons(lvl, cell, head, tail)),

src/prolog/machine.rs

@@ -110,7 +110,7 @@ impl Machine {
         self.code_dir.insert((name, arity), p);
     }
 
-    fn execute_instr<'a>(&mut self, instr_src: LineOrCodeOffset<'a>) -> bool
+    fn execute_instr<'b>(&mut self, instr_src: LineOrCodeOffset<'b>) -> bool
     {
         let mut instr = match instr_src {
             LineOrCodeOffset::Instruction(instr) => instr,
@@ -121,6 +121,8 @@ impl Machine {
             match instr {
                 &Line::Choice(ref choice_instr) =>
                     self.ms.execute_choice_instr(choice_instr),
+                &Line::Control(ref control_instr) =>
+                    self.ms.execute_ctrl_instr(&self.code_dir, control_instr),
                 &Line::Fact(ref fact) => {
                     for fact_instr in fact {
                         if self.failed() {
@@ -130,7 +132,11 @@ impl Machine {
                         self.ms.execute_fact_instr(&fact_instr);
                     }
                     self.ms.p += 1;
-                },
+                },                
+                &Line::Indexing(ref indexing_instr) =>
+                    self.ms.execute_indexing_instr(&indexing_instr),
+                &Line::IndexedChoice(ref choice_instr) =>
+                    self.ms.execute_indexed_choice_instr(choice_instr),
                 &Line::Query(ref query) => {
                     for query_instr in query {
                         if self.failed() {
@@ -140,9 +146,7 @@ impl Machine {
                         self.ms.execute_query_instr(&query_instr);
                     }
                     self.ms.p += 1;
-                },
-                &Line::Control(ref control_instr) =>
-                    self.ms.execute_ctrl_instr(&self.code_dir, control_instr),
+                }                
             }
 
             if self.failed() {
@@ -556,6 +560,8 @@ impl MachineState {
                         self.h += 1;
                     }
                 };
+
+                self.s += 1;
             },
             &FactInstruction::UnifyVariable(reg) => {
                 match self.mode {
@@ -640,6 +646,69 @@ impl MachineState {
         };
     }
 
+    fn execute_indexing_instr(&mut self, instr: &IndexingInstruction) {
+        match instr {
+            &IndexingInstruction::SwitchOnTerm(v, c, l, s) => {
+                let a1 = self.registers[1].clone();
+                let addr = self.store(self.deref(a1));
+
+                let offset = match addr {
+                    Addr::HeapCell(_) | Addr::StackCell(_, _) => v,
+                    Addr::Con(_) => c,
+                    Addr::Lis(_) => l,
+                    Addr::Str(_) => s
+                };
+
+                match offset {
+                    0 => self.fail = true,
+                    o => self.p += o
+                };
+            },
+            &IndexingInstruction::SwitchOnConstant(_, ref hm) => {
+                let a1 = self.registers[1].clone();
+                let addr = self.store(self.deref(a1));
+
+                let offset = match addr {
+                    Addr::Con(constant) => {
+                        match hm.get(&constant) {
+                            Some(offset) => *offset,
+                            _ => 0
+                        }
+                    },
+                    _ => 0
+                };
+
+                match offset {
+                    0 => self.fail = true,
+                    o => self.p += o,
+                };
+            },
+            &IndexingInstruction::SwitchOnStructure(_, ref hm) => {
+                let a1 = self.registers[1].clone();
+                let addr = self.store(self.deref(a1));
+
+                let offset = match addr {
+                    Addr::Str(s) => {
+                        if let &HeapCellValue::NamedStr(arity, ref name) = &self.heap[s] {
+                            match hm.get(&(name.clone(), arity)) {
+                                Some(offset) => *offset,
+                                _ => 0
+                            }
+                        } else {
+                            0
+                        }
+                    },
+                    _ => 0
+                };
+
+                match offset {
+                    0 => self.fail = true,
+                    o => self.p += o                    
+                };            
+            }
+        };
+    }
+    
     fn execute_query_instr(&mut self, instr: &QueryInstruction) {
         match instr {
             &QueryInstruction::PutConstant(_, ref constant, reg) =>
@@ -782,9 +851,94 @@ impl MachineState {
         };
     }
 
-    fn execute_choice_instr(&mut self, instr: &ChoiceInstruction)
+    fn execute_indexed_choice_instr(&mut self, instr: &IndexedChoiceInstruction)
     {
         match instr {
+            &IndexedChoiceInstruction::Try(l) => {
+                let n = self.num_of_args;
+                let num_frames = self.num_frames();
+
+                self.or_stack.push(num_frames + 1,
+                                   self.e,
+                                   self.cp,
+                                   self.b,
+                                   self.p + 1,
+                                   self.tr,
+                                   self.h,
+                                   self.num_of_args);
+
+                self.b = self.or_stack.len() - 1;
+                let b = self.b;
+
+                for i in 1 .. n + 1 {
+                    self.or_stack[b][i] = self.registers[i].clone();
+                }
+
+                self.hb = self.h;
+                self.p += l;
+            },
+            &IndexedChoiceInstruction::Retry(l) => {
+                let b = self.b;
+                let n = self.or_stack[b].num_args();
+
+                for i in 1 .. n + 1 {
+                    self.registers[i] = self.or_stack[b][i].clone();
+                }
+
+                self.e = self.or_stack[b].e;
+                self.cp = self.or_stack[b].cp;
+
+                self.or_stack[b].bp = self.p + 1;
+
+                let old_tr  = self.or_stack[b].tr;
+                let curr_tr = self.tr;
+
+                self.unwind_trail(old_tr, curr_tr);
+                self.tr = self.or_stack[b].tr;
+
+                self.trail.truncate(self.tr);
+                self.heap.truncate(self.or_stack[b].h);
+
+                self.h  = self.or_stack[b].h;
+                self.hb = self.h;
+
+                self.p += l;
+            },
+            &IndexedChoiceInstruction::Trust(l) => {
+                let b = self.b;
+                let n = self.or_stack[b].num_args();
+
+                for i in 1 .. n + 1 {
+                    self.registers[i] = self.or_stack[b][i].clone();
+                }
+
+                self.e  = self.or_stack[b].e;
+                self.cp = self.or_stack[b].cp;
+
+                let old_tr  = self.or_stack[b].tr;
+                let curr_tr = self.tr;
+
+                self.unwind_trail(old_tr, curr_tr);
+
+                self.tr = self.or_stack[b].tr;
+                self.trail.truncate(self.tr);
+
+                self.h = self.or_stack[b].h;
+                self.heap.truncate(self.h);
+
+                self.b = self.or_stack[b].b;
+
+                self.or_stack.pop();
+
+                self.hb = self.h;
+                self.p += l;
+            }
+        };
+    }
+    
+    fn execute_choice_instr(&mut self, instr: &ChoiceInstruction)
+    {
+        match instr {            
             &ChoiceInstruction::TryMeElse(offset) => {
                 let n = self.num_of_args;
                 let num_frames = self.num_frames();
@@ -807,7 +961,7 @@ impl MachineState {
 
                 self.hb = self.h;
                 self.p += 1;
-            },
+            },            
             &ChoiceInstruction::RetryMeElse(offset) => {
                 let b = self.b;
                 let n = self.or_stack[b].num_args();

src/prolog/prolog_parser.lalrpop

@@ -12,7 +12,7 @@ pub TopLevel: TopLevel = {
 };
 
 Atom : Atom = {
-    r"[a-z][a-z0-9_]*" => <>.trim().to_string(),
+    r"[a-z][A-Za-z0-9_]*" => <>.trim().to_string(),
 };
 
 BoxedTerm : Box<Term> = {
@@ -73,5 +73,5 @@ Term : Term = {
 };
 
 Var : Var = {
-    r"[A-Z][a-z0-9_]*" => <>.trim().to_string()
+    r"[A-Z][A-Za-z0-9_]*" => <>.trim().to_string()
 };

src/prolog/prolog_parser.rs

@@ -21,8 +21,8 @@ mod __parse__TopLevel {
         Term_22_5d_22(&'input str),
         Term_22___22(&'input str),
         Term_22_7c_22(&'input str),
-        Termr_23_22_5bA_2dZ_5d_5ba_2dz0_2d9___5d_2a_22_23(&'input str),
-        Termr_23_22_5ba_2dz_5d_5ba_2dz0_2d9___5d_2a_22_23(&'input str),
+        Termr_23_22_5bA_2dZ_5d_5bA_2dZa_2dz0_2d9___5d_2a_22_23(&'input str),
+        Termr_23_22_5ba_2dz_5d_5bA_2dZa_2dz0_2d9___5d_2a_22_23(&'input str),
         Termerror(__lalrpop_util::ErrorRecovery<usize, (usize, &'input str), ()>),
         Nt_28_22_2c_22_20_3cTerm_3e_29(Term),
         Nt_28_22_2c_22_20_3cTerm_3e_29_2a(::std::vec::Vec<Term>),
@@ -719,8 +719,8 @@ mod __parse__TopLevel {
             r###""]""###,
             r###""_""###,
             r###""|""###,
-            r###"r#"[A-Z][a-z0-9_]*"#"###,
-            r###"r#"[a-z][a-z0-9_]*"#"###,
+            r###"r#"[A-Z][A-Za-z0-9_]*"#"###,
+            r###"r#"[a-z][A-Za-z0-9_]*"#"###,
         ];
         __ACTION[(__state * 14)..].iter().zip(__TERMINAL).filter_map(|(&state, terminal)| {
             if state == 0 {
@@ -822,11 +822,11 @@ mod __parse__TopLevel {
                             _ => unreachable!(),
                         },
                         11 => match __lookahead.1 {
-                            (11, __tok0) => __Symbol::Termr_23_22_5bA_2dZ_5d_5ba_2dz0_2d9___5d_2a_22_23(__tok0),
+                            (11, __tok0) => __Symbol::Termr_23_22_5bA_2dZ_5d_5bA_2dZa_2dz0_2d9___5d_2a_22_23(__tok0),
                             _ => unreachable!(),
                         },
                         12 => match __lookahead.1 {
-                            (12, __tok0) => __Symbol::Termr_23_22_5ba_2dz_5d_5ba_2dz0_2d9___5d_2a_22_23(__tok0),
+                            (12, __tok0) => __Symbol::Termr_23_22_5ba_2dz_5d_5bA_2dZa_2dz0_2d9___5d_2a_22_23(__tok0),
                             _ => unreachable!(),
                         },
                         _ => unreachable!(),
@@ -1028,8 +1028,8 @@ mod __parse__TopLevel {
                 7
             }
             14 => {
-                // Atom = r#"[a-z][a-z0-9_]*"# => ActionFn(5);
-                let __sym0 = __pop_Termr_23_22_5ba_2dz_5d_5ba_2dz0_2d9___5d_2a_22_23(__symbols);
+                // Atom = r#"[a-z][A-Za-z0-9_]*"# => ActionFn(5);
+                let __sym0 = __pop_Termr_23_22_5ba_2dz_5d_5bA_2dZa_2dz0_2d9___5d_2a_22_23(__symbols);
                 let __start = __sym0.0.clone();
                 let __end = __sym0.2.clone();
                 let __nt = super::__action5::<>(input, __sym0);
@@ -1333,8 +1333,8 @@ mod __parse__TopLevel {
                 17
             }
             39 => {
-                // Var = r#"[A-Z][a-z0-9_]*"# => ActionFn(23);
-                let __sym0 = __pop_Termr_23_22_5bA_2dZ_5d_5ba_2dz0_2d9___5d_2a_22_23(__symbols);
+                // Var = r#"[A-Z][A-Za-z0-9_]*"# => ActionFn(23);
+                let __sym0 = __pop_Termr_23_22_5bA_2dZ_5d_5bA_2dZa_2dz0_2d9___5d_2a_22_23(__symbols);
                 let __start = __sym0.0.clone();
                 let __end = __sym0.2.clone();
                 let __nt = super::__action23::<>(input, __sym0);
@@ -1468,23 +1468,23 @@ mod __parse__TopLevel {
             _ => panic!("symbol type mismatch")
         }
     }
-    fn __pop_Termr_23_22_5bA_2dZ_5d_5ba_2dz0_2d9___5d_2a_22_23<
+    fn __pop_Termr_23_22_5bA_2dZ_5d_5bA_2dZa_2dz0_2d9___5d_2a_22_23<
       'input,
     >(
         __symbols: &mut ::std::vec::Vec<(usize,__Symbol<'input>,usize)>
     ) -> (usize, &'input str, usize) {
         match __symbols.pop().unwrap() {
-            (__l, __Symbol::Termr_23_22_5bA_2dZ_5d_5ba_2dz0_2d9___5d_2a_22_23(__v), __r) => (__l, __v, __r),
+            (__l, __Symbol::Termr_23_22_5bA_2dZ_5d_5bA_2dZa_2dz0_2d9___5d_2a_22_23(__v), __r) => (__l, __v, __r),
             _ => panic!("symbol type mismatch")
         }
     }
-    fn __pop_Termr_23_22_5ba_2dz_5d_5ba_2dz0_2d9___5d_2a_22_23<
+    fn __pop_Termr_23_22_5ba_2dz_5d_5bA_2dZa_2dz0_2d9___5d_2a_22_23<
       'input,
     >(
         __symbols: &mut ::std::vec::Vec<(usize,__Symbol<'input>,usize)>
     ) -> (usize, &'input str, usize) {
         match __symbols.pop().unwrap() {
-            (__l, __Symbol::Termr_23_22_5ba_2dz_5d_5ba_2dz0_2d9___5d_2a_22_23(__v), __r) => (__l, __v, __r),
+            (__l, __Symbol::Termr_23_22_5ba_2dz_5d_5bA_2dZa_2dz0_2d9___5d_2a_22_23(__v), __r) => (__l, __v, __r),
             _ => panic!("symbol type mismatch")
         }
     }
@@ -1845,6 +1845,11 @@ mod __intern_token {
                             __current_state = 16;
                             continue;
                         }
+                        65 ... 90 => {
+                            __current_match = Some((11, __index + __ch.len_utf8()));
+                            __current_state = 16;
+                            continue;
+                        }
                         95 => /* '_' */ {
                             __current_match = Some((11, __index + 1));
                             __current_state = 16;
@@ -1897,6 +1902,11 @@ mod __intern_token {
                             __current_state = 18;
                             continue;
                         }
+                        65 ... 90 => {
+                            __current_match = Some((12, __index + __ch.len_utf8()));
+                            __current_state = 18;
+                            continue;
+                        }
                         95 => /* '_' */ {
                             __current_match = Some((12, __index + 1));
                             __current_state = 18;
@@ -1952,6 +1962,11 @@ mod __intern_token {
                             __current_state = 16;
                             continue;
                         }
+                        65 ... 90 => {
+                            __current_match = Some((11, __index + __ch.len_utf8()));
+                            __current_state = 16;
+                            continue;
+                        }
                         95 => /* '_' */ {
                             __current_match = Some((11, __index + 1));
                             __current_state = 16;
@@ -1983,6 +1998,11 @@ mod __intern_token {
                             __current_state = 18;
                             continue;
                         }
+                        65 ... 90 => {
+                            __current_match = Some((12, __index + __ch.len_utf8()));
+                            __current_state = 18;
+                            continue;
+                        }
                         95 => /* '_' */ {
                             __current_match = Some((12, __index + 1));
                             __current_state = 18;