transition to l1

README.md

@@ -1,13 +1,14 @@
 # rusty-wam
 
-The beginnings of the Warren Abstract Machine in Rust, according to
-the progression of languages in [Warren's Abstract Machine: A Tutorial
+An implementation of the Warren Abstract Machine in Rust, done
+according to the progression of languages in [Warren's Abstract
+Machine: A Tutorial
 Reconstruction](http://wambook.sourceforge.net/wambook.pdf), ending in
 pure Prolog.
 
 ## Progress
 
-The language L0 is implemented as a simple REPL. It supports
+The language L1 is implemented as a simple REPL. It supports
 unification on facts and queries without backtracking and rules
 without clauses, in the familiar Prolog syntax. No data types apart
 from atoms are currently supported.
@@ -15,45 +16,44 @@ from atoms are currently supported.
 An example of the level of interaction currently supported is:
 
 ```
-l0> p(Z, Z).  
-Program stored.  
-l0> ?- p(Z, Z).  
+l1> p(Z, Z).  
+l1> ?- p(Z, Z).  
 yes  
-l0> ?- p(Z, z).  
+l1> ?- p(Z, z).  
 yes  
-l0> ?- p(Z, w).  
+l1> ?- p(Z, w).  
 yes  
-l0> ?- p(z, w).  
+l1> clouds(are, nice).
+l1> ?- p(z, w).  
 no  
-l0> ?- p(w, w).  
+l1> ?- p(w, w).  
 yes
-l0> clouds(are, nice).
-Program stored.
-l0> ?- clouds(Z, Z).
+l1> ?- clouds(Z, Z).
 no
-l0> ?- clouds(Z, W).
+l1> ?- clouds(Z, W).
 yes
-l0> ?- clouds(are, W).
+l1> ?- clouds(are, W).
 yes
-l0> ?- clouds(W, nice).
+l1> ?- clouds(W, nice).
 yes
-l0> ?- clouds(nice, are).
+l1> ?- clouds(nice, are).
 no
-l0> ?- p(Z, h(Z, W), f(W)).  
+l1> ?- p(Z, h(Z, W), f(W)).  
 no  
-l0> p(Z, h(Z, W), f(W)).  
-Program stored.  
-l0> ?- p(z, h(z, z), f(w)).  
+l1> p(Z, h(Z, W), f(W)).  
+l1> ?- p(z, h(z, z), f(w)).  
 no  
-l0> ?- p(z, h(z, w), f(w)).  
+l1> ?- p(z, h(z, w), f(w)).  
 yes  
-l0> ?- p(Z, h(z, W), f(w)).  
+l1> ?- p(Z, h(z, W), f(w)).  
 yes  
-l0> ?- p(z, h(Z, w), f(w)).  
+l1> ?- p(z, h(Z, w), f(w)).  
 yes
-l0> ?- p(z, h(Z, w), f(Z)).
+l1> ?- p(Z, h(Z, w), f(Z)).
+yes
+l1> ?- p(z, h(Z, w), f(Z)).
 no
-l0> quit
+l1> quit
 ```
 
 ## Occurs check
@@ -61,8 +61,7 @@ l0> quit
 There's no occurs check, so cyclic terms do unify:
 
 ```
-l0> p(W, W).
-Program stored.
-l0> ?- p(f(f(W)), W).
+l1> p(W, W).
+l1> ?- p(f(f(W)), W).
 yes
 ```

src/l1/ast.rs

@@ -0,0 +1,112 @@
+use std::cell::Cell;
+use std::fmt;
+use std::vec::Vec;
+
+pub type Var = String;
+
+pub type Atom = String;
+
+pub enum TopLevel {
+    Fact(Term),
+    Query(Term)
+}
+
+#[derive(Clone, Copy)]
+pub enum Level {
+    Shallow, Deep
+}
+
+impl fmt::Display for Level {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        match self {
+            &Level::Shallow => write!(f, "A"),
+            &Level::Deep => write!(f, "X")
+        }
+    }
+}
+
+#[derive(Clone, Copy)]
+pub enum Reg {
+    ArgAndNorm(usize, usize),
+    Norm(usize)
+}
+
+impl Reg {    
+    pub fn has_arg(&self) -> bool {
+        match self {
+            &Reg::ArgAndNorm(_, _) => true,
+            _ => false
+        }
+    }
+
+    pub fn norm(&self) -> usize {
+        match self {
+            &Reg::ArgAndNorm(_, norm) | &Reg::Norm(norm) => norm
+        }
+    }
+}
+
+pub enum Term {
+    Atom(Cell<usize>, Atom),
+    Clause(Cell<usize>, Atom, Vec<Box<Term>>),
+    Var(Cell<Reg>, Var)
+}
+
+pub enum TermRef<'a> {
+    Atom(Level, &'a Cell<usize>, &'a Atom),
+    Clause(Level, &'a Cell<usize>, &'a Atom, &'a Vec<Box<Term>>),
+    Var(Level, &'a Cell<Reg>, &'a Var)
+}
+
+#[derive(Clone)]
+pub enum FactInstruction {
+    GetStructure(Level, Atom, usize, usize),
+    GetValue(usize, usize),
+    GetVariable(usize, usize),
+    Proceed,
+    UnifyVariable(usize),
+    UnifyValue(usize)
+}
+
+pub enum QueryInstruction {
+    Call(Atom, usize),
+    PutStructure(Level, Atom, usize, usize),
+    PutValue(usize, usize),
+    PutVariable(usize, usize),
+    SetVariable(usize),
+    SetValue(usize),
+}
+
+pub type CompiledFact = Vec<FactInstruction>;
+
+pub type CompiledQuery = Vec<QueryInstruction>;
+
+#[derive(Clone, Copy, PartialEq)]
+pub enum Addr {
+    HeapCell(usize),
+    RegNum(usize)
+}
+
+impl Term {
+    pub fn subterms(&self) -> usize {
+        match self {
+            &Term::Clause(_, _, ref terms) => terms.len(),
+            _ => 1
+        }
+    }
+
+    pub fn name(&self) -> &Atom {
+        match self {
+            &Term::Atom(_, ref atom)
+            | &Term::Var(_, ref atom)                
+            | &Term::Clause(_, ref atom, _) => atom
+        }
+    }
+    
+    pub fn arity(&self) -> usize {
+        match self {
+            &Term::Atom(_, _) | &Term::Var(_, _) => 0,
+            &Term::Clause(_, _, ref child_terms) => child_terms.len()
+        }
+    }
+}

src/l1/codegen.rs

@@ -0,0 +1,303 @@
+use l1::ast::{Atom, CompiledFact, CompiledQuery, FactInstruction,
+              Level, QueryInstruction, Reg, Term, TermRef, Var};
+use l1::iterators::{FactIterator, QueryIterator};
+
+use std::cell::Cell;
+use std::collections::HashMap;
+use std::fmt;
+use std::vec::Vec;
+
+impl fmt::Display for QueryInstruction {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        match self {
+            &QueryInstruction::Call(ref name, ref arity) =>
+                write!(f, "call {}/{}", name, arity),
+            &QueryInstruction::PutStructure(ref lvl, ref a, ref s, ref r) =>
+                write!(f, "put_structure {}/{}, {}{}", a, s, lvl, r),
+            &QueryInstruction::PutValue(ref a, ref x) =>
+                write!(f, "put_value X{}, A{}", x, a),
+            &QueryInstruction::PutVariable(ref a, ref x) =>
+                write!(f, "put_variable X{}, A{}", x, a),
+            &QueryInstruction::SetVariable(ref r) =>
+                write!(f, "set_variable X{}", r),
+            &QueryInstruction::SetValue(ref r) =>
+                write!(f, "set_value X{}", r),
+        }
+    }
+}
+
+impl fmt::Display for FactInstruction {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        match self {
+            &FactInstruction::GetStructure(ref lvl, ref a, ref s, ref r) =>
+                write!(f, "get_structure {}/{}, {}{}", a, s, lvl, r),
+            &FactInstruction::GetValue(ref a, ref x) =>
+                write!(f, "get_value X{}, A{}", x, a),
+            &FactInstruction::GetVariable(ref a, ref x) =>
+                write!(f, "get_variable X{}, A{}", x, a),
+            &FactInstruction::Proceed =>
+                write!(f, "proceed"),
+            &FactInstruction::UnifyVariable(ref r) =>
+                write!(f, "unify_variable X{}", r),
+            &FactInstruction::UnifyValue(ref r) =>
+                write!(f, "unify_value X{}", r)
+        }
+    }
+}
+
+struct TermMarker<'a> {    
+    bindings: HashMap<&'a Var, Reg>,
+    arg_c:    usize,
+    norm_c:   usize
+}
+
+impl<'a> TermMarker<'a> {
+    fn new(term: &'a Term) -> TermMarker<'a> {
+        TermMarker { bindings: HashMap::new(),
+                     arg_c:    1,
+                     norm_c:   term.subterms() + 1 }
+    }
+
+    fn contains_var(&self, var: &'a Var) -> bool {
+        self.bindings.contains_key(var)
+    }
+
+    fn get(&self, var: &'a Var) -> Reg {
+        *self.bindings.get(var).unwrap()
+    }
+
+    fn insert(&mut self, var: &'a Var, r: Reg) {
+        self.bindings.insert(var, r);
+    }
+    
+    fn mark_non_var(&mut self, lvl: Level, cell: &Cell<usize>) {
+        if cell.get() == 0 {            
+            match lvl {
+                Level::Deep => {
+                    let norm = self.norm_c;
+                    self.norm_c += 1;
+                    cell.set(norm);
+                },            
+                Level::Shallow => {
+                    let arg = self.arg_c;
+                    self.arg_c += 1;
+                    cell.set(arg);
+                }
+            };
+        }
+    }
+
+    fn mark_var(&mut self, lvl: Level, var: &'a Var) -> Reg {
+        if self.contains_var(var) {
+            let reg = self.get(var);
+
+            match lvl {
+                Level::Deep => Reg::Norm(reg.norm()),
+                Level::Shallow if reg.has_arg() => {
+                    let arg = self.arg_c;
+                    self.arg_c += 1;
+                    
+                    Reg::ArgAndNorm(arg, reg.norm())
+                },
+                Level::Shallow => {
+                    let norm = reg.norm();
+                    let reg  = Reg::ArgAndNorm(self.arg_c, norm);
+
+                    self.arg_c += 1;
+                    self.insert(var, reg);
+
+                    reg
+                }
+            }
+        } else {
+            let reg = match lvl {
+                Level::Deep    => Reg::Norm(self.norm_c),
+                Level::Shallow => {
+                    let reg = Reg::ArgAndNorm(self.arg_c, self.norm_c);
+                    self.arg_c += 1;
+                    reg
+                }
+            };
+
+            self.norm_c += 1;
+            self.insert(var, reg);
+            reg
+        }
+    }
+}
+
+trait CompilationTarget<'a> {
+    type Iterator : Iterator<Item=TermRef<'a>>;
+
+    fn iter(&'a Term) -> Self::Iterator;
+
+    fn to_structure(Level, Atom, usize, usize) -> Self;
+
+    fn argument_to_variable(usize, usize) -> Self;
+    fn argument_to_value(usize, usize) -> Self;
+    fn subterm_to_variable(usize) -> Self;
+    fn subterm_to_value(usize) -> Self;
+}
+
+impl<'a> CompilationTarget<'a> for FactInstruction {
+    type Iterator = FactIterator<'a>;
+
+    fn iter(term: &'a Term) -> Self::Iterator {
+        term.breadth_first_iter()
+    }
+
+    fn to_structure(lvl: Level, atom: Atom, arity: usize, cell_num: usize) -> Self {        
+        FactInstruction::GetStructure(lvl, atom, arity, cell_num)
+    }
+
+    fn argument_to_variable(arg: usize, val: usize) -> Self {
+        FactInstruction::GetVariable(arg, val)
+    }
+
+    fn argument_to_value(arg: usize, val: usize) -> Self {
+        FactInstruction::GetValue(arg, val)
+    }
+
+    fn subterm_to_variable(val: usize) -> Self {
+        FactInstruction::UnifyVariable(val)
+    }
+
+    fn subterm_to_value(val: usize) -> Self {
+        FactInstruction::UnifyValue(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, cell_num: usize) -> Self {
+        QueryInstruction::PutStructure(lvl, atom, arity, cell_num)
+    }
+
+    fn argument_to_variable(arg: usize, val: usize) -> Self {
+        QueryInstruction::PutVariable(arg, val)
+    }
+
+    fn argument_to_value(arg: usize, val: usize) -> Self {
+        QueryInstruction::PutValue(arg, val)
+    }
+
+    fn subterm_to_variable(val: usize) -> Self {
+        QueryInstruction::SetVariable(val)
+    }
+
+    fn subterm_to_value(val: usize) -> Self {
+        QueryInstruction::SetValue(val)
+    }
+}
+
+fn to_structure<'a, Target>(tm: &mut TermMarker<'a>,
+                            lvl: Level,
+                            name: &'a Atom,
+                            cell: &'a Cell<usize>,
+                            arity: usize)
+                            -> Target
+    where Target: CompilationTarget<'a>
+{
+    tm.mark_non_var(lvl, cell);
+    Target::to_structure(lvl, name.clone(), arity, cell.get())
+}
+
+fn non_var_subterm<'a, Target>(tm: &mut TermMarker<'a>, cell: &'a Cell<usize>)
+                               -> Target
+    where Target: CompilationTarget<'a>
+{
+    tm.mark_non_var(Level::Deep, cell);
+    Target::subterm_to_value(cell.get()) // should be to_value??
+}
+
+fn var_term<'a, Target>(tm: &mut TermMarker<'a>,
+                        lvl: Level,
+                        cell: &'a Cell<Reg>,
+                        var: &'a Var)
+                        -> Target
+    where Target: CompilationTarget<'a>
+{
+    if !tm.contains_var(var) {
+        let reg = tm.mark_var(lvl, var);
+        cell.set(reg);
+        
+        match reg {
+            Reg::ArgAndNorm(arg, norm) =>
+                Target::argument_to_variable(arg, norm),
+            Reg::Norm(norm) =>
+                Target::subterm_to_variable(norm)
+        }
+    } else {
+        let reg = tm.mark_var(lvl, var);
+        cell.set(reg);
+        
+        match reg {
+            Reg::ArgAndNorm(arg, norm) =>
+                Target::argument_to_value(arg, norm),
+            Reg::Norm(norm) =>
+                Target::subterm_to_value(norm)
+        }
+    }
+}
+
+fn subterm_to_instr<'a, Target>(tm: &mut TermMarker<'a>,
+                                subterm: &'a Term)
+                                -> Target
+    where Target: CompilationTarget<'a>
+{
+    match subterm {
+        &Term::Atom(ref cell, _) | &Term::Clause(ref cell, _, _) =>
+            non_var_subterm(tm, cell),
+        &Term::Var(ref cell, ref var) =>
+            var_term(tm, Level::Deep, cell, var)
+    }
+}
+
+fn compile_target<'a, Target>(term: &'a Term) -> Vec<Target>
+    where Target: CompilationTarget<'a>
+{
+    let iter       = Target::iter(term);
+    let mut target = Vec::<Target>::new();
+    let mut marker = TermMarker::new(term);
+
+    for term in iter {
+        match term {
+            TermRef::Atom(lvl, term, atom) =>
+                target.push(to_structure(&mut marker, lvl, atom, term, 0)),
+            TermRef::Clause(lvl, term, atom, terms) => {
+                target.push(to_structure(&mut marker, lvl, atom, term, terms.len()));
+
+                for subterm in terms {
+                    target.push(subterm_to_instr(&mut marker, subterm.as_ref()));
+                }
+            },
+            TermRef::Var(lvl @ Level::Shallow, ref cell, ref var) =>
+                target.push(var_term(&mut marker, lvl, cell, var)),
+            _ => {}
+        };
+    }
+
+    target
+}
+
+pub fn compile_fact(term: &Term) -> CompiledFact {
+    let mut compiled_fact = compile_target(term);
+
+    compiled_fact.push(FactInstruction::Proceed);
+    compiled_fact
+}
+
+pub fn compile_query(term: &Term) -> CompiledQuery {
+    let mut compiled_query = compile_target(term);
+
+    if let &Term::Clause(_, ref atom, ref terms) = term {
+        compiled_query.push(QueryInstruction::Call(atom.clone(), terms.len()));
+    }
+
+    compiled_query
+}

src/l1/iterators.rs

@@ -0,0 +1,175 @@
+use l1::ast::{Atom, Level, Reg, Term, TermRef, Var};
+
+use std::cell::Cell;
+use std::collections::VecDeque;
+use std::vec::Vec;
+
+enum IteratorState<'a> {
+    Atom(Level, &'a Cell<usize>, &'a Atom),
+    Clause(Level, usize, &'a Cell<usize>, &'a Atom, &'a Vec<Box<Term>>),
+    IsolatedAtom(&'a Cell<usize>, &'a Atom),
+    IsolatedVar(&'a Cell<Reg>, &'a Var),
+    RootClause(usize, &'a Vec<Box<Term>>),
+    Var(Level, &'a Cell<Reg>, &'a Var)
+}
+
+impl<'a> IteratorState<'a> {
+    fn to_state(lvl: Level, term: &'a Term) -> IteratorState<'a>
+    {
+        match term {
+            &Term::Atom(ref cell, ref atom) =>
+                IteratorState::Atom(lvl, cell, atom),
+            &Term::Clause(ref cell, ref atom, ref child_terms) =>
+                IteratorState::Clause(lvl, 0, cell, atom, child_terms),
+            &Term::Var(ref cell, ref var) =>
+                IteratorState::Var(lvl, cell, var)
+        }
+    }
+}
+
+pub struct QueryIterator<'a> {
+    state_stack: Vec<IteratorState<'a>>
+}
+
+impl<'a> QueryIterator<'a> {
+    fn push_clause(&mut self,
+                   lvl: Level,
+                   child_num: usize,
+                   cell: &'a Cell<usize>,
+                   name: &'a Atom,
+                   child_terms: &'a Vec<Box<Term>>)
+    {
+        self.state_stack.push(IteratorState::Clause(lvl,
+                                                    child_num,
+                                                    cell,
+                                                    name,
+                                                    child_terms));
+    }
+
+    fn push_root_clause(&mut self,
+                        child_num: usize,                        
+                        child_terms: &'a Vec<Box<Term>>)
+    {
+        self.state_stack.push(IteratorState::RootClause(child_num, child_terms));
+    }
+
+    fn push_subterm(&mut self, lvl: Level, term: &'a Term) {
+        self.state_stack.push(IteratorState::to_state(lvl, term));
+    }
+
+    fn new(term: &'a Term) -> QueryIterator<'a> {
+        let state = match term {
+            &Term::Atom(ref cell, ref atom) =>
+                IteratorState::IsolatedAtom(cell, atom),
+            &Term::Clause(_, _, ref terms) =>
+                IteratorState::RootClause(0, terms),
+            &Term::Var(ref cell, ref var) =>
+                IteratorState::IsolatedVar(cell, var)
+        };
+        
+        QueryIterator { state_stack: vec![state] }
+    }
+}
+
+impl<'a> Iterator for QueryIterator<'a> {
+    type Item = TermRef<'a>;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        while let Some(iter_state) = self.state_stack.pop() {
+            match iter_state {
+                IteratorState::Atom(lvl, cell, atom) =>
+                    return Some(TermRef::Atom(lvl, cell, atom)),
+                IteratorState::Clause(lvl, child_num, cell, atom, child_terms) => {
+                    if child_num == child_terms.len() {
+                        return Some(TermRef::Clause(lvl, cell, atom, child_terms));
+                    } else {
+                        self.push_clause(lvl, child_num + 1, cell, atom, child_terms);
+                        self.push_subterm(Level::Deep, child_terms[child_num].as_ref());
+                    }
+                },
+                IteratorState::IsolatedAtom(cell, atom) =>
+                    return Some(TermRef::Atom(Level::Shallow, cell, atom)),
+                IteratorState::IsolatedVar(cell, var) =>
+                    return Some(TermRef::Var(Level::Shallow, cell, var)),
+                IteratorState::RootClause(child_num, child_terms) => {
+                    if child_num == child_terms.len() {
+                        return None;
+                    } else {
+                        self.push_root_clause(child_num + 1, child_terms);
+                        self.push_subterm(Level::Shallow, child_terms[child_num].as_ref());
+                    }
+                },
+                IteratorState::Var(lvl, cell, var) =>
+                    return Some(TermRef::Var(lvl, cell, var))
+            };
+        }
+
+        None
+    }
+}
+
+pub struct FactIterator<'a> {
+    state_queue: VecDeque<IteratorState<'a>>,
+}
+
+impl<'a> FactIterator<'a> {
+    fn push_subterm(&mut self, lvl: Level, term: &'a Term) {
+        self.state_queue.push_back(IteratorState::to_state(lvl, term));
+    }
+
+    fn new(term: &'a Term) -> FactIterator<'a> {
+        let states = match term {
+            &Term::Atom(ref cell, ref atom) =>
+                vec![IteratorState::IsolatedAtom(cell, atom)],
+            &Term::Clause(_, _, ref terms) =>
+                vec![IteratorState::RootClause(0, terms)],
+            &Term::Var(ref cell, ref var) =>
+                vec![IteratorState::IsolatedVar(cell, var)]
+        };
+
+        FactIterator { state_queue:  VecDeque::from(states) }
+    }
+}
+
+impl<'a> Iterator for FactIterator<'a> {
+    type Item = TermRef<'a>;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        while let Some(state) = self.state_queue.pop_front() {
+            match state {
+                IteratorState::Atom(lvl, cell, atom) =>
+                    return Some(TermRef::Atom(lvl, cell, atom)),
+                IteratorState::Clause(lvl, _, cell, atom, child_terms) => {
+                    for child_term in child_terms {
+                        self.push_subterm(Level::Deep, child_term);
+                    }
+
+                    return Some(TermRef::Clause(lvl, cell, atom, child_terms));
+                },
+                IteratorState::IsolatedAtom(cell, atom) =>
+                    return Some(TermRef::Atom(Level::Shallow, cell, atom)),
+                IteratorState::IsolatedVar(cell, var) =>
+                    return Some(TermRef::Var(Level::Shallow, cell, var)),
+                IteratorState::RootClause(_, child_terms) => {
+                    for child_term in child_terms {
+                        self.push_subterm(Level::Shallow, child_term);
+                    }
+                },
+                IteratorState::Var(lvl, cell, var) =>
+                    return Some(TermRef::Var(lvl, cell, var))
+            }
+        }
+
+        None
+    }
+}
+
+impl Term {
+    pub fn post_order_iter(&self) -> QueryIterator {
+        QueryIterator::new(self)
+    }
+
+    pub fn breadth_first_iter(&self) -> FactIterator {
+        FactIterator::new(self)
+    }
+}

src/l1/l1_parser.lalrpop

@@ -0,0 +1,32 @@
+use std::cell::Cell;
+
+use l1::ast::{Atom, Reg, Term, TopLevel, Var};
+
+grammar;
+
+pub TopLevel: TopLevel = {
+    "?-" <t:Term> "." => TopLevel::Query(t),
+    <t:Term> "."      => TopLevel::Fact(t),
+};
+
+Atom : Atom = {
+    r"[a-z][a-z0-9_]*" => <>.trim().to_string(),
+};
+
+Var : Var = {
+    r"[A-Z][a-z0-9_]*" => <>.trim().to_string(),
+};
+
+BoxedTerm : Box<Term> = {
+    <t:Term> => Box::new(t),
+};
+
+Term : Term = {
+    <a:Atom> "(" <ts: (<BoxedTerm> ",")*> <t:BoxedTerm> ")" => {
+     	let mut ts = ts;
+     	ts.push(t);
+	Term::Clause(Cell::new(0), a, ts)
+    },
+    <Atom> => Term::Atom(Cell::new(0), <>),
+    <Var>  => Term::Var(Cell::new(Reg::Norm(0)), <>)
+};

src/l1/machine.rs

@@ -0,0 +1,290 @@
+use l1::ast::{Addr, Atom, FactInstruction, QueryInstruction};
+
+use std::collections::HashMap;
+use std::vec::Vec;
+
+#[derive(Clone)]
+enum HeapCell {
+    NamedStr(usize, Atom),
+    Ref(usize),
+    Str(usize),
+}
+
+#[derive(Clone, Copy)]
+enum MachineMode {
+    Read,
+    Write
+}
+
+type Heap = Vec<HeapCell>;
+
+type Registers = Vec<HeapCell>;
+
+pub struct Machine {
+    h : usize,
+    s : usize,
+    p : usize,
+    pub fail : bool,
+    heap : Heap,
+    mode : MachineMode,
+    pub code_dir : HashMap<(Atom, usize), usize>,
+    pub code : Vec<FactInstruction>,
+    registers : Registers
+}
+
+impl Machine {
+    pub fn new() -> Machine {
+        Machine { h : 0,
+                  s : 0,
+                  p : 0,
+                  fail : false,
+                  heap : Vec::with_capacity(256),
+                  mode : MachineMode::Write,
+                  code_dir : HashMap::new(),
+                  code : Vec::new(),
+                  registers : vec![HeapCell::Ref(0); 32] }
+    }
+
+    fn lookup(&self, a: Addr) -> &HeapCell {
+        match a {
+            Addr::HeapCell(hc) => &self.heap[hc],
+            Addr::RegNum(reg)  => &self.registers[reg]
+        }
+    }
+
+    fn deref(&self, a: Addr) -> Addr {
+        let mut a = a;
+
+        loop {
+            if let &HeapCell::Ref(value) = self.lookup(a) {
+                if let Addr::HeapCell(av) = a {
+                    if value != av {
+                        a = Addr::HeapCell(value);
+                        continue;
+                    }
+                }
+            }
+
+            return a;
+        };
+    }
+
+    fn is_unbound(hc: &HeapCell, index: usize) -> bool {
+        match hc {
+            &HeapCell::Ref(r) => r == index,
+            _ => false
+        }
+    }
+
+    //TODO: try to compress this function. currently it is dog shit.
+    fn bind(&mut self, a: Addr, val: usize) {
+        let mut a = a;
+        
+        loop {
+            match a {
+                Addr::RegNum(reg) => {
+                    if let HeapCell::Ref(hc) = self.registers[reg] {
+                        a = Addr::HeapCell(hc);
+                    } else if Machine::is_unbound(&self.heap[val], val) {
+                        self.heap[val] = self.registers[reg].clone();
+                        break;
+                    } else {
+                        self.fail = true;
+                        break;
+                    }                        
+                },
+                Addr::HeapCell(hc) if Machine::is_unbound(&self.heap[hc], hc) => {
+                    self.heap[hc] = HeapCell::Ref(val);
+                    break;
+                },
+                Addr::HeapCell(hc) if Machine::is_unbound(&self.heap[val], val) => {                
+                    self.heap[val] = HeapCell::Ref(hc);
+                    break;
+                },
+                _ => {
+                    self.fail = true;                    
+                    break;
+                }
+            };
+        }
+    }
+
+    fn unify(&mut self, a1: Addr, a2: Addr) {
+        let mut pdl : Vec<Addr> = vec![a1, a2];
+
+        self.fail = false;
+
+        while !(pdl.is_empty() || self.fail) {
+            let d1 = self.deref(pdl.pop().unwrap());
+            let d2 = self.deref(pdl.pop().unwrap());
+
+            if d1 != d2 {
+                match (self.lookup(d1), self.lookup(d2)) {
+                    (&HeapCell::Ref(hc), _) =>
+                        self.bind(d2, hc),
+                    (_, &HeapCell::Ref(hc)) =>
+                        self.bind(d1, hc),
+                    (&HeapCell::Str(a1), &HeapCell::Str(a2)) => {
+                        let r1 = &self.heap[a1];
+                        let r2 = &self.heap[a2];
+
+                        if let &HeapCell::NamedStr(n1, ref f1) = r1 {
+                            if let &HeapCell::NamedStr(n2, ref f2) = r2 {
+                                if n1 == n2 && *f1 == *f2 {
+                                    for i in 1 .. n1 {
+                                        pdl.push(Addr::HeapCell(a1 + i));
+                                        pdl.push(Addr::HeapCell(a2 + i));
+                                    }
+
+                                    continue;
+                                }
+                            }
+                        }
+
+                        self.fail = true;
+                    },
+                    _ => self.fail = true,
+                };
+            }
+        }
+    }
+
+    pub fn execute_fact(&mut self) {
+        loop {
+            if let &FactInstruction::Proceed = &self.code[self.p] {
+                break;
+            } else if self.fail {
+                break;
+            }
+
+            let fact_instr = self.code[self.p].clone();
+            self.execute_fact_instr(fact_instr);
+        }
+    }
+
+    pub fn execute_query_instr<'a, 'b: 'a>(&'a mut self, instr: &'b QueryInstruction) {
+        match instr {
+            &QueryInstruction::Call(ref name, arity) => {
+                // why is Option<&T> not Deref?!?!?
+                let compiled_fact_index =
+                    self.code_dir.get(&(name.clone(), arity)).map(|index| *index);
+
+                match compiled_fact_index {
+                    Some(compiled_fact_index) => {
+                        self.p = compiled_fact_index;
+                        self.execute_fact();
+                    },
+                    None => self.fail = true,
+                };
+            }
+            &QueryInstruction::PutStructure(_, ref name, arity, reg) => {
+                self.heap.push(HeapCell::Str(self.h + 1));
+                self.heap.push(HeapCell::NamedStr(arity, name.clone()));
+
+                self.registers[reg] = self.heap[self.h].clone();
+
+                self.h += 2;
+            },
+            &QueryInstruction::PutValue(arg, norm) =>
+                self.registers[arg] = self.registers[norm].clone(),
+            &QueryInstruction::PutVariable(arg, norm) => {
+                self.heap.push(HeapCell::Ref(self.h));
+
+                self.registers[norm] = self.heap[self.h].clone();
+                self.registers[arg]  = self.heap[self.h].clone();
+
+                self.h += 1;
+            },
+            &QueryInstruction::SetVariable(reg) => {
+                self.heap.push(HeapCell::Ref(self.h));
+                self.registers[reg] = self.heap[self.h].clone();
+
+                self.h += 1;
+            },
+            &QueryInstruction::SetValue(reg) => {
+                self.heap.push(self.registers[reg].clone());
+                self.h += 1;
+            },
+        }
+    }
+
+    fn execute_fact_instr(&mut self, instr: FactInstruction) {
+        match instr {
+            FactInstruction::Proceed => return,
+            FactInstruction::GetStructure(_, name, arity, reg) => {
+                let addr = self.deref(Addr::RegNum(reg));
+
+                match self.lookup(addr) {
+                    &HeapCell::Str(a) => {
+                        let result = &self.heap[a];
+
+                        if let &HeapCell::NamedStr(named_arity, ref named_str) = result {
+                            if arity == named_arity && *name == *named_str {
+                                self.s = a + 1;
+                                self.mode = MachineMode::Read;
+                            } else {
+                                self.fail = true;
+                            }
+                        }
+                    },
+                    &HeapCell::Ref(r) => {
+                        self.heap.push(HeapCell::Str(self.h + 1));
+                        self.heap.push(HeapCell::NamedStr(arity, name));
+
+                        let h = self.h;
+
+                        self.bind(Addr::HeapCell(r), h);                        
+
+                        self.h += 2;
+                        self.mode = MachineMode::Write;
+                    },
+                    _ => {
+                        self.fail = true;
+                    }
+                };
+            },
+            FactInstruction::GetVariable(arg, norm) =>
+                self.registers[norm] = self.registers[arg].clone(),
+            FactInstruction::GetValue(arg, norm) =>
+                self.unify(Addr::RegNum(norm), Addr::RegNum(arg)),
+            FactInstruction::UnifyVariable(reg) => {
+                match self.mode {
+                    MachineMode::Read  => self.registers[reg] = self.heap[self.s].clone(),
+                    MachineMode::Write => {
+                        self.heap.push(HeapCell::Ref(self.h));
+                        self.registers[reg] = self.heap[self.h].clone();
+                        self.h += 1;
+                    }
+                };
+
+                self.s += 1;
+            },
+            FactInstruction::UnifyValue(reg) => {
+                let s = self.s;
+
+                match self.mode {
+                    MachineMode::Read  => self.unify(Addr::RegNum(reg), Addr::HeapCell(s)),
+                    MachineMode::Write => {
+                        self.heap.push(self.registers[reg].clone());
+                        self.h += 1;
+                    }
+                };
+
+                self.s += 1;
+            }
+        }
+
+        self.p += 1;
+    }
+
+    pub fn reset_machine_state(&mut self) {
+        self.h = 0;
+        self.s = 0;
+        self.p = 0;
+
+        self.fail = false;
+        self.heap = Vec::with_capacity(256);
+        self.mode = MachineMode::Write;
+        self.registers = vec![HeapCell::Ref(0); 32];
+    }
+}

src/l1/mod.rs

@@ -0,0 +1,5 @@
+pub mod ast;
+pub mod iterators;
+pub mod l1_parser;
+pub mod codegen;
+pub mod machine;

src/main.rs

@@ -1,72 +1,62 @@
-mod l0;
+mod l1;
 
-use l0::ast::{TopLevel};
-use l0::codegen::{compile_target};
-use l0::machine::{Machine};
+use l1::ast::TopLevel;
+use l1::codegen::{compile_fact, compile_query};
+use l1::machine::Machine;
 
 use std::io::{self, Write};
 
-fn l0_repl() {
+fn l1_repl() {
     let mut ms = Machine::new();
-    
+
     loop {
-        print!("l0> ");
-        
+        print!("l1> ");
+
         let _ = io::stdout().flush();
         let mut buffer = String::new();
-        
+
         io::stdin().read_line(&mut buffer).unwrap();
-        
-        let result = l0::parser::parse_top_level(&*buffer);
+
+        let result = l1::l1_parser::parse_TopLevel(&*buffer);
 
         if &*buffer == "quit\n" {
             break;
         } else if &*buffer == "clear\n" {
             ms = Machine::new();
-        }        
-        
-        match result {            
-            Ok(TopLevel::Fact(fact)) => {                
-                let program = compile_target(&fact);
-                                
-                ms = Machine::new();                
-                ms.program = Some(program);                
+        }
+
+        match result {
+            Ok(TopLevel::Fact(fact)) => {
+                let mut compiled_fact = compile_fact(&fact);
+                let index = ms.code.len();
                 
-                println!("Program stored.");
+                ms.code.append(&mut compiled_fact);
+                ms.code_dir.insert((fact.name().clone(), fact.arity()), index);
             },
             Ok(TopLevel::Query(query)) => {
-                if let Some(program) = ms.program.take() {                
-                    let query = compile_target(&query);
-                    
-                    for instruction in &query {
-                        ms.execute_query_instr(instruction);
-                    }
+                let compiled_query = compile_query(&query);
 
-                    for instruction in &program {                    
-                        ms.execute_fact_instr(instruction);
+                for instruction in &compiled_query {
+                    ms.execute_query_instr(instruction);
 
-                        if ms.fail {                            
-                            break;
-                        }
-                    }                    
-                
                     if ms.fail {
-                        println!("no");
-                    } else {
-                        println!("yes");
+                        break;
                     }
-                    
-                    ms.reset_heap();
-                    ms.program = Some(program);
-                } else {
-                    println!("No program to speak of.");
                 }
-            },                                        
+
+                if ms.fail {
+                    println!("no");
+                } else {
+                    println!("yes");
+                }
+
+                ms.reset_machine_state();
+            },
             Err(_) => println!("Grammatical error of some kind!"),
-        };        
+        };
     }
 }
 
 fn main() {
-    l0_repl();
+    l1_repl();
 }