--- /dev/null Thu Jan 01 00:00:00 1970 +0000
+++ b/src/Pure/envir.ML Thu Sep 16 12:20:38 1993 +0200
@@ -0,0 +1,207 @@
+(* Title: envir
+ ID: $Id$
+ Author: Lawrence C Paulson, Cambridge University Computer Laboratory
+ Copyright 1988 University of Cambridge
+*)
+
+(*Environments
+ Should take account that typ is part of variable name,
+ otherwise two variables with same name and different types
+ will cause errors!
+*)
+
+
+signature ENVIR =
+sig
+ type 'a xolist
+ exception ENVIR of string * indexname;
+ datatype env = Envir of {asol: term xolist,
+ iTs: (indexname * typ) list,
+ maxidx: int}
+ val alist_of : env -> (indexname * term) list
+ val alist_of_olist : 'a xolist -> (indexname * 'a) list
+ val empty : int->env
+ val genvar : string -> env * typ -> env * term
+ val genvars : string -> env * typ list -> env * term list
+ val lookup : env * indexname -> term option
+ val norm_term : env -> term -> term
+ val null_olist : 'a xolist
+ val olist_of_alist: (indexname * 'a) list -> 'a xolist
+ val update : (indexname * term) * env -> env
+ val vupdate : (indexname * term) * env -> env
+end;
+
+functor EnvirFun () : ENVIR =
+struct
+
+
+(*association lists with keys in ascending order, no repeated keys*)
+datatype 'a xolist = Olist of (indexname * 'a) list;
+
+
+exception ENVIR of string * indexname;
+
+(*look up key in ordered list*)
+fun xsearch (Olist[], key) = None
+ | xsearch (Olist ((keyi,xi)::pairs), key) =
+ if xless(keyi,key) then xsearch (Olist pairs, key)
+ else if key=keyi then Some xi
+ else None;
+
+(*insert pair in ordered list, reject if key already present*)
+fun xinsert_new (newpr as (key, x), Olist al) =
+ let fun insert [] = [newpr]
+ | insert ((pair as (keyi,xi)) :: pairs) =
+ if xless(keyi,key) then pair :: insert pairs
+ else if key=keyi then
+ raise ENVIR("xinsert_new: already present",key)
+ else newpr::pair::pairs
+ in Olist (insert al) end;
+
+(*insert pair in ordered list, overwrite if key already present*)
+fun xinsert (newpr as (key, x), Olist al) =
+ let fun insert [] = [newpr]
+ | insert ((pair as (keyi,xi)) :: pairs) =
+ if xless(keyi,key) then pair :: insert pairs
+ else if key=keyi then newpr::pairs
+ else newpr::pair::pairs
+ in Olist (insert al) end;
+
+(*apply function to the contents part of each pair*)
+fun xmap f (Olist pairs) =
+ let fun xmp [] = []
+ | xmp ((key,x)::pairs) = (key, f x) :: xmp pairs
+ in Olist (xmp pairs) end;
+
+(*allows redefinition of a key by "join"ing the contents parts*)
+fun xmerge_olists join (Olist pairsa, Olist pairsb) =
+ let fun xmrg ([],pairsb) = pairsb
+ | xmrg (pairsa,[]) = pairsa
+ | xmrg ((keya,x)::pairsa, (keyb,y)::pairsb) =
+ if xless(keya,keyb) then
+ (keya,x) :: xmrg (pairsa, (keyb,y)::pairsb)
+ else if xless(keyb,keya) then
+ (keyb,y) :: xmrg ((keya,x)::pairsa, pairsb)
+ else (*equal*) (keya, join(x,y)) :: xmrg (pairsa, pairsb)
+ in Olist (xmrg (pairsa,pairsb)) end;
+
+val null_olist = Olist[];
+
+fun alist_of_olist (Olist pairs) = pairs;
+
+fun olist_of_alist pairs = foldr xinsert (pairs, Olist[]);
+
+
+
+(*updating can destroy environment in 2 ways!!
+ (1) variables out of range (2) circular assignments
+*)
+datatype env = Envir of
+ {maxidx: int, (*maximum index of vars*)
+ asol: term xolist, (*table of assignments to Vars*)
+ iTs: (indexname*typ)list} (*table of assignments to TVars*)
+
+
+(*Generate a list of distinct variables.
+ Increments index to make them distinct from ALL present variables. *)
+fun genvars name (Envir{maxidx, asol, iTs}, Ts) : env * term list =
+ let fun genvs (_, [] : typ list) : term list = []
+ | genvs (n, [T]) = [ Var((name, maxidx+1), T) ]
+ | genvs (n, T::Ts) =
+ Var((name ^ radixstring(26,"a",n), maxidx+1), T)
+ :: genvs(n+1,Ts)
+ in (Envir{maxidx=maxidx+1, asol=asol, iTs=iTs}, genvs (0,Ts)) end;
+
+(*Generate a variable.*)
+fun genvar name (env,T) : env * term =
+ let val (env',[v]) = genvars name (env,[T])
+ in (env',v) end;
+
+fun lookup (Envir{asol,...}, xname) : term option = xsearch (asol,xname);
+
+fun update ((xname, t), Envir{maxidx, asol, iTs}) =
+ Envir{maxidx=maxidx, asol=xinsert_new ((xname,t), asol), iTs=iTs};
+
+(*The empty environment. New variables will start with the given index.*)
+fun empty m = Envir{maxidx=m, asol=null_olist, iTs=[]};
+
+(*Update, checking Var-Var assignments: try to suppress higher indexes*)
+fun vupdate((a,t), env) = case t of
+ Var(name',T) =>
+ if a=name' then env (*cycle!*)
+ else if xless(a, name') then
+ (case lookup(env,name') of (*if already assigned, chase*)
+ None => update((name', Var(a,T)), env)
+ | Some u => vupdate((a,u), env))
+ else update((a,t), env)
+ | _ => update((a,t), env);
+
+
+(*Convert environment to alist*)
+fun alist_of (Envir{maxidx,asol,...}) = alist_of_olist asol;
+
+
+(*Beta normal form for terms (not eta normal form).
+ Chases variables in env; Does not exploit sharing of variable bindings
+ Does not check types, so could loop. *)
+local
+ (*raised when norm has no effect on a term,
+ to encourage sharing instead of copying*)
+ exception SAME;
+
+ fun norm_term1 (asol,t) : term =
+ let fun norm (Var (w,T)) =
+ (case xsearch(asol,w) of
+ Some u => normh u
+ | None => raise SAME)
+ | norm (Abs(a,T,body)) = Abs(a, T, norm body)
+ | norm (Abs(_,_,body) $ t) = normh(subst_bounds([t], body))
+ | norm (f $ t) =
+ ((case norm f of
+ Abs(_,_,body) => normh(subst_bounds([t], body))
+ | nf => nf $ normh t)
+ handle SAME => f $ norm t)
+ | norm _ = raise SAME
+ and normh t = (norm t) handle SAME => t
+ in normh t end
+
+ and norm_term2(asol,iTs,t) : term =
+ let fun normT(Type(a,Ts)) = Type(a, normTs Ts)
+ | normT(TFree _) = raise SAME
+ | normT(TVar(v,_)) = (case assoc(iTs,v) of
+ Some(U) => normTh U
+ | None => raise SAME)
+ and normTh T = ((normT T) handle SAME => T)
+ and normTs([]) = raise SAME
+ | normTs(T::Ts) = ((normT T :: normTsh Ts)
+ handle SAME => T :: normTs Ts)
+ and normTsh Ts = ((normTs Ts) handle SAME => Ts)
+ and norm(Const(a,T)) = Const(a, normT T)
+ | norm(Free(a,T)) = Free(a, normT T)
+ | norm(Var (w,T)) =
+ (case xsearch(asol,w) of
+ Some u => normh u
+ | None => Var(w,normT T))
+ | norm(Abs(a,T,body)) =
+ (Abs(a,normT T,normh body) handle SAME => Abs(a, T, norm body))
+ | norm(Abs(_,_,body) $ t) = normh(subst_bounds([t], body))
+ | norm(f $ t) =
+ ((case norm f of
+ Abs(_,_,body) => normh(subst_bounds([t], body))
+ | nf => nf $ normh t)
+ handle SAME => f $ norm t)
+ | norm _ = raise SAME
+ and normh t = (norm t) handle SAME => t
+ in normh t end;
+
+in
+
+(*curried version might be slower in recursive calls*)
+fun norm_term (env as Envir{asol,iTs,...}) t : term =
+ if iTs=[] then norm_term1(asol, t) else norm_term2(asol,iTs, t)
+
+end;
+
+end;
+
+