obua@16781: (*  Title:      Pure/Tools/am_interpreter.ML
obua@16781:     ID:         $Id$
obua@16781:     Author:     Steven Obua
obua@16781: *)
obua@16781: 
wenzelm@16842: signature ABSTRACT_MACHINE =
wenzelm@16842: sig
wenzelm@16842: 
obua@16781: datatype term = Var of int | Const of int | App of term * term | Abs of term
obua@16781: 
obua@16781: datatype pattern = PVar | PConst of int * (pattern list)
obua@16781: 
obua@16781: type program
obua@16781: 
obua@16781: exception Compile of string;
obua@16781: val compile : (pattern * term) list -> program
wenzelm@16842: 
obua@16781: exception Run of string;
obua@16781: val run : program -> term -> term
obua@16781: 
obua@16781: end
obua@16781: 
obua@16781: structure AM_Interpreter :> ABSTRACT_MACHINE = struct
obua@16781: 
obua@16781: datatype term = Var of int | Const of int | App of term * term | Abs of term
obua@16781: 
obua@16781: datatype pattern = PVar | PConst of int * (pattern list)
obua@16781: 
obua@16781: datatype closure = CVar of int | CConst of int
wenzelm@16842:                  | CApp of closure * closure | CAbs of closure
wenzelm@16842:                  | Closure of (closure list) * closure
obua@16781: 
obua@16782: structure prog_struct = TableFun(type key = int*int val ord = prod_ord int_ord int_ord);
obua@16781: 
obua@16782: type program = ((pattern * closure) list) prog_struct.table
obua@16781: 
obua@16781: datatype stack = SEmpty | SAppL of closure * stack | SAppR of closure * stack | SAbs of stack
obua@16781: 
obua@16781: exception Compile of string;
obua@16781: exception Run of string;
obua@16781: 
obua@16781: fun clos_of_term (Var x) = CVar x
obua@16781:   | clos_of_term (Const c) = CConst c
obua@16781:   | clos_of_term (App (u, v)) = CApp (clos_of_term u, clos_of_term v)
obua@16781:   | clos_of_term (Abs u) = CAbs (clos_of_term u)
obua@16781: 
obua@16781: fun term_of_clos (CVar x) = Var x
obua@16781:   | term_of_clos (CConst c) = Const c
obua@16781:   | term_of_clos (CApp (u, v)) = App (term_of_clos u, term_of_clos v)
obua@16781:   | term_of_clos (CAbs u) = Abs (term_of_clos u)
obua@16781:   | term_of_clos (Closure (e, u)) = raise (Run "internal error: closure in normalized term found")
obua@16781: 
obua@16781: fun strip_closure args (CApp (a,b)) = strip_closure (b::args) a
obua@16781:   | strip_closure args x = (x, args)
obua@16781: 
obua@16781: fun len_head_of_closure n (CApp (a,b)) = len_head_of_closure (n+1) a
obua@16781:   | len_head_of_closure n x = (n, x)
obua@16781: 
obua@16781: 
obua@16781: (* earlier occurrence of PVar corresponds to higher de Bruijn index *)
obua@16781: fun pattern_match args PVar clos = SOME (clos::args)
wenzelm@16842:   | pattern_match args (PConst (c, patterns)) clos =
obua@16781:     let
wenzelm@16842:         val (f, closargs) = strip_closure [] clos
obua@16781:     in
wenzelm@16842:         case f of
wenzelm@16842:             CConst d =>
wenzelm@16842:             if c = d then
wenzelm@16842:                 pattern_match_list args patterns closargs
wenzelm@16842:             else
wenzelm@16842:                 NONE
wenzelm@16842:           | _ => NONE
obua@16781:     end
obua@16781: and pattern_match_list args [] [] = SOME args
wenzelm@16842:   | pattern_match_list args (p::ps) (c::cs) =
obua@16781:     (case pattern_match args p c of
wenzelm@16842:         NONE => NONE
obua@16781:       | SOME args => pattern_match_list args ps cs)
obua@16781:   | pattern_match_list _ _ _ = NONE
obua@16781: 
obua@16781: (* Returns true iff at most 0 .. (free-1) occur unbound. therefore check_freevars 0 t iff t is closed *)
obua@16781: fun check_freevars free (Var x) = x < free
obua@16781:   | check_freevars free (Const c) = true
obua@16781:   | check_freevars free (App (u, v)) = check_freevars free u andalso check_freevars free v
obua@16781:   | check_freevars free (Abs m) = check_freevars (free+1) m
obua@16781: 
obua@16781: fun count_patternvars PVar = 1
obua@16781:   | count_patternvars (PConst (_, ps)) = List.foldl (fn (p, count) => (count_patternvars p)+count) 0 ps
obua@16781: 
obua@16781: fun pattern_key (PConst (c, ps)) = (c, length ps)
obua@16781:   | pattern_key _ = raise (Compile "pattern reduces to variable")
obua@16781: 
wenzelm@16842: fun compile eqs =
obua@16781:     let
wenzelm@16842:         val eqs = map (fn (p, r) => (check_freevars (count_patternvars p) r;
wenzelm@16842:                                      (pattern_key p, (p, clos_of_term r)))) eqs
obua@16781:     in
wenzelm@16842:         prog_struct.make (map (fn (k, a) => (k, [a])) eqs)
wenzelm@16842:     end
obua@16781: 
obua@16781: fun match_rules n [] clos = NONE
obua@16781:   | match_rules n ((p,eq)::rs) clos =
obua@16781:     case pattern_match [] p clos of
wenzelm@16842:         NONE => match_rules (n+1) rs clos
obua@16781:       | SOME args => SOME (Closure (args, eq))
obua@16781: 
wenzelm@16842: fun match_closure prog clos =
obua@16781:     case len_head_of_closure 0 clos of
wenzelm@16842:         (len, CConst c) =>
wenzelm@16842:         (case prog_struct.lookup (prog, (c, len)) of
wenzelm@16842:             NONE => NONE
wenzelm@16842:           | SOME rules => match_rules 0 rules clos)
obua@16781:       | _ => NONE
obua@16781: 
obua@16781: fun lift n (c as (CConst _)) = c
obua@16781:   | lift n (v as CVar m) = if m < n then v else CVar (m+1)
obua@16781:   | lift n (CAbs t) = CAbs (lift (n+1) t)
obua@16781:   | lift n (CApp (a,b)) = CApp (lift n a, lift n b)
obua@16781:   | lift n (Closure (e, a)) = Closure (lift_env n e, lift (n+(length e)) a)
obua@16781: and lift_env n e = map (lift n) e
obua@16781: 
obua@16781: fun weak prog stack (Closure (e, CApp (a, b))) = weak prog (SAppL (Closure (e, b), stack)) (Closure (e, a))
obua@16781:   | weak prog (SAppL (b, stack)) (Closure (e, CAbs m)) = weak prog stack (Closure (b::e, m))
obua@16781:   | weak prog stack (Closure (e, CVar n)) = weak prog stack (List.nth (e, n) handle Subscript => (CVar (n-(length e))))
obua@16781:   | weak prog stack (Closure (e, c as CConst _)) = weak prog stack c
wenzelm@16842:   | weak prog stack clos =
obua@16781:     case match_closure prog clos of
wenzelm@16842:         NONE => weak_last prog stack clos
obua@16781:       | SOME r => weak prog stack r
obua@16781: and weak_last prog (SAppR (a, stack)) b = weak prog stack (CApp (a,b))
obua@16781:   | weak_last prog (s as (SAppL (b, stack))) a = weak prog (SAppR (a, stack)) b
wenzelm@16842:   | weak_last prog stack c = (stack, c)
obua@16781: 
wenzelm@16842: fun strong prog stack (Closure (e, CAbs m)) =
obua@16781:     let
wenzelm@16842:         val (stack', wnf) = weak prog SEmpty (Closure ((CVar 0)::(lift_env 0 e), m))
obua@16781:     in
wenzelm@16842:         case stack' of
wenzelm@16842:             SEmpty => strong prog (SAbs stack) wnf
wenzelm@16842:           | _ => raise (Run "internal error in strong: weak failed")
obua@16781:     end
obua@16781:   | strong prog stack (clos as (CApp (u, v))) = strong prog (SAppL (v, stack)) u
obua@16781:   | strong prog stack clos = strong_last prog stack clos
obua@16781: and strong_last prog (SAbs stack) m = strong prog stack (CAbs m)
obua@16781:   | strong_last prog (SAppL (b, stack)) a = strong prog (SAppR (a, stack)) b
obua@16781:   | strong_last prog (SAppR (a, stack)) b = strong_last prog stack (CApp (a, b))
obua@16781:   | strong_last prog stack clos = (stack, clos)
obua@16781: 
wenzelm@16842: fun run prog t =
obua@16781:     let
wenzelm@16842:         val (stack, wnf) = weak prog SEmpty (Closure ([], clos_of_term t))
obua@16781:     in
wenzelm@16842:         case stack of
wenzelm@16842:             SEmpty => (case strong prog SEmpty wnf of
wenzelm@16842:                            (SEmpty, snf) => term_of_clos snf
wenzelm@16842:                          | _ => raise (Run "internal error in run: strong failed"))
wenzelm@16842:           | _ => raise (Run "internal error in run: weak failed")
obua@16781:     end
wenzelm@16842: 
obua@16781: end
obua@16781: 
obua@16781: structure AbstractMachine = AM_Interpreter