(* Unification *) (* Author: Frank Pfenning, Carsten Schuermann *) (* Modified: Roberto Virga *) functor Unify ((*! structure IntSyn' : INTSYN !*) structure Whnf : WHNF (*! sharing Whnf.IntSyn = IntSyn' !*) structure Trail : TRAIL) : UNIFY = struct (*! structure IntSyn = IntSyn' !*) exception Unify of string local open IntSyn datatype Action = Instantiate of Exp option ref | InstantiateBlock of Block option ref | Add of cnstr list ref | Solve of cnstr * Cnstr datatype CAction = BindCnstr of Cnstr ref * Cnstr datatype FAction = BindExp of Exp option ref * Exp option | BindBlock of Block option ref * Block option | BindAdd of cnstr list ref * CAction list | FSolve of Cnstr ref * Cnstr * Cnstr (* ? *) type unifTrail = FAction Trail.trail val globalTrail = Trail.trail () : Action Trail.trail fun frontToString (Idx i) = "(idx " ^ Int.toString i ^ ")" | frontToString (Exp E) = " exp _ " | frontToString (Undef) = " undef " fun subToString (Shift i) = "(shift " ^ Int.toString i ^ ")" | subToString (Dot(ft, s)) = frontToString ft ^ ". " ^ subToString s fun copyCnstr [] = [] | copyCnstr (refC :: clist) = (BindCnstr (refC, !refC) :: copyCnstr clist) fun copy (Instantiate refU) = (BindExp (refU , !refU)) | copy (InstantiateBlock refB) = (BindBlock (refB , !refB)) | copy (Add (cnstrs as ref Cnstrs)) = (BindAdd (cnstrs , copyCnstr(!cnstrs))) | copy (Solve (cnstr, Cnstr)) = (FSolve (cnstr, Cnstr, !cnstr)) fun resetCnstr [] = [] | resetCnstr (BindCnstr(refC, Cnstr)::L) = (refC := Cnstr; (refC::(resetCnstr L))) fun reset (BindExp (refU, U)) = (refU := U; Instantiate refU) | reset (BindBlock (refB, B)) = (refB := B; InstantiateBlock refB) | reset (BindAdd (cnstrs , CActions)) = (cnstrs := resetCnstr CActions; Add cnstrs) | reset (FSolve (refCnstr, Cnstr, Cnstr')) = (refCnstr := Cnstr'; Solve (refCnstr, Cnstr)) fun suspend () = Trail.suspend (globalTrail, copy) fun resume trail = Trail.resume (trail, globalTrail, reset) fun undo (Instantiate refU) = (refU := NONE) | undo (InstantiateBlock refB) = (refB := NONE) | undo (Add (cnstrs as ref(cnstr :: cnstrL))) = (cnstrs := cnstrL) | undo (Solve (cnstr, Cnstr)) = (cnstr := Cnstr) fun reset () = Trail.reset globalTrail fun mark () = Trail.mark globalTrail fun unwind () = Trail.unwind (globalTrail, undo) fun addConstraint (cnstrs, cnstr) = ( cnstrs := cnstr :: (!cnstrs); Trail.log (globalTrail, Add (cnstrs)) ) fun solveConstraint (cnstr as ref (Cnstr)) = ( cnstr := Solved; Trail.log (globalTrail, Solve (cnstr, Cnstr)) ) (* Associate a constraint to an expression *) (* delayExpW ((U, s), cnstr) = () Invariant: If G' |- s : G G |- U : V (U,s) in whnf then the constraint cnstr is added to all the rigid EVar occurrences in U[s] *) fun delayExpW ((U as Uni(L), s1), _) = () | delayExpW ((Pi ((D, P), U), s), cnstr) = (delayDec ((D, s), cnstr); delayExp ((U, dot1 s), cnstr)) | delayExpW ((Root (H, S), s), cnstr) = (delayHead (H, cnstr); delaySpine ((S, s), cnstr)) | delayExpW ((Lam (D, U), s), cnstr) = (delayDec ((D, s), cnstr); delayExp ((U, dot1 s), cnstr)) | delayExpW ((EVar (G, r, V, cnstrs), s), cnstr) = addConstraint(cnstrs, cnstr) | delayExpW ((FgnExp (cs, ops), s), cnstr) = (* s = id *) delayExp ((#toInternal(ops) (), s), cnstr) (* no other cases by invariant *) (* delayExp ((U, s), cnstr) = () as in delayExpCW, except that the argument may not be in whnf *) and delayExp (Us, cnstr) = delayExpW (Whnf.whnf Us, cnstr) (* delayHead (H, s, rOccur) = () Invariant: If G' |- H : V and G' |- s : G s is a pattern substitution then the constraint cnstr is added to a total of n rigid EVar occurrences in H[s] *) and delayHead (FVar (x, V, s'), cnstr) = delayExp ((V, id), cnstr) | delayHead (H, _) = () (* delaySpine ((S, s), cnstr) = () Invariant: If G' |- s : G G |- S : V > W then G |- S' : V' > W' the constraint cnstr is added to all the rigid EVar occurrences in S[s] *) and delaySpine ((Nil, s), cnstr) = () | delaySpine ((App (U, S), s), cnstr) = (delayExp ((U, s), cnstr); delaySpine ((S, s), cnstr)) | delaySpine ((SClo(S, s'), s), cnstr) = delaySpine ((S, comp (s', s)), cnstr) (* delayDec see delayExp *) and delayDec ((Dec (name, V), s), cnstr) = delayExp ((V, s), cnstr) local val awakenCnstrs = ref nil : cnstr list ref in fun resetAwakenCnstrs () = (awakenCnstrs := nil) fun nextCnstr () = case !awakenCnstrs of nil => NONE | (cnstr :: cnstrL) => (awakenCnstrs := cnstrL; SOME(cnstr)) (* Instantiating EVars *) fun instantiateEVar (refU, V, cnstrL) = ( refU := SOME(V); Trail.log (globalTrail, Instantiate (refU)); awakenCnstrs := cnstrL @ !awakenCnstrs ) (* Instantiating LVars *) fun instantiateLVar (refB, B) = ( refB := SOME(B); Trail.log (globalTrail, InstantiateBlock (refB)) ) end (* local *) (* intersection (s1, s2) = s' s' = s1 /\ s2 (see JICSLP'96) Invariant: If G |- s1 : G' s1 patsub and G |- s2 : G' s2 patsub then G |- s' : G'' for some G'' and s' patsub *) fun intersection (Dot (Idx (k1), s1), Dot (Idx (k2), s2)) = if (k1 = k2) then dot1 (intersection (s1, s2)) else comp (intersection (s1, s2), shift) | intersection (s1 as Dot _, Shift (n2)) = intersection (s1, Dot (Idx (n2+1), Shift (n2+1))) | intersection (Shift (n1), s2 as Dot _) = intersection (Dot (Idx (n1+1), Shift (n1+1)), s2) | intersection (Shift _ , Shift _) = id (* both substitutions are the same number of shifts by invariant *) (* all other cases impossible for pattern substitutions *) (* weakenSub (G1, s, ss) = w' Invariant: If G |- s : G1 (* s patsub *) and G2 |- ss : G (* ss strsub *) then G1 |- w' : G1' (* w' weaksub *) and G2 |- w' o s o ss : G1' is fully defined and G1' is maximal such *) fun weakenSub (G, Shift n, ss) = if n < ctxLength G then weakenSub (G, Dot (Idx (n+1), Shift (n+1)), ss) else id | weakenSub (G, Dot (Idx n, s'), ss) = (case bvarSub (n, ss) of Undef => comp (weakenSub (G, s', ss), shift) | Idx _ => dot1 (weakenSub (G, s', ss))) (* no other cases, ss is strsub *) | weakenSub (G, Dot (Undef, s'), ss) = comp (weakenSub (G, s', ss), shift) (* prune (G, (U, s), ss, rOccur) = U[s][ss] !!! looks wrong to me -kw G |- U : V G' |- s : G (G' |- U[s] : V[s]) G'' |- ss : G' !!! i would say G |- s : G' G' |- U : V (G |- U[s] : V[s]) G'' |- ss : G Effect: prunes EVars in U[s] according to ss raises Unify if U[s][ss] does not exist, or rOccur occurs in U[s] *) fun pruneExp (G, Us, ss, rOccur, prunable) = pruneExpW (G, Whnf.whnf Us, ss, rOccur, prunable) and pruneExpW (G, (U as Uni _, s), _, _, _) = U | pruneExpW (G, (Pi ((D, P), V), s), ss, rOccur, prunable) = Pi ((pruneDec (G, (D, s), ss, rOccur, prunable), P), pruneExp (Decl (G, decSub (D, s)), (V, dot1 s), dot1 ss, rOccur, prunable)) | pruneExpW (G, (Lam (D, V), s), ss, rOccur, prunable) = Lam (pruneDec (G, (D, s), ss, rOccur, prunable), pruneExp (Decl (G, decSub (D, s)), (V, dot1 s), dot1 ss, rOccur, prunable)) | pruneExpW (G, (Root (H, S), s (* = id *)), ss, rOccur, prunable) = Root (pruneHead (G, H, ss, rOccur, prunable), pruneSpine (G, (S, s), ss, rOccur, prunable)) | pruneExpW (G, (X as EVar (r, GX, V, cnstrs), s), ss, rOccur, prunable) = if (rOccur = r) then raise Unify "Variable occurrence" else if Whnf.isPatSub (s) then let val w = weakenSub (G, s, ss) in if Whnf.isId w then EClo (X, comp (s, ss)) else if prunable then let val wi = Whnf.invert w (* val V' = EClo (V, wi) *) val V' = pruneExp (GX, (V, id), wi, rOccur, prunable) (* val GY = Whnf.strengthen (wi, GX) *) val GY = pruneCtx (wi, GX, rOccur, prunable) (* shortcut on GY possible by invariant on GX and V[s]? -fp *) (* could optimize by checking for identity subst *) val Y = newEVar (GY, V') val Yw = EClo (Y, w) val _ = instantiateEVar (r, Yw, !cnstrs) in EClo (Yw, comp (s, ss)) end else raise Unify "Not prunable" end else (* s not patsub *) ( EClo (X, pruneSub (G, s, ss, rOccur, false)) handle Unify (msg) => if prunable then let (* val GY = Whnf.strengthen (ss, G) *) (* shortcuts possible by invariants on G? *) val GY = pruneCtx (ss, G, rOccur, prunable) (* val V' = EClo (V, comp (s, ss)) *) val V' = pruneExp (G, (V, s), ss, rOccur, prunable) val Y = newEVar (GY, V') val _ = addConstraint (cnstrs, ref (Eqn (G, EClo (X, s), EClo (Y, Whnf.invert ss)))) in Y end else raise Unify (msg) ) | pruneExpW (G, (FgnExp (_, ops), s), ss, rOccur, prunable) = #map(ops) (fn U => pruneExp (G, (U, s), ss, rOccur, prunable)) (* other cases impossible since (U,s1) whnf *) and pruneDec (G, (Dec (name, V), s), ss, rOccur, prunable) = Dec (name, pruneExp (G, (V, s), ss, rOccur, prunable)) and pruneSpine (G, (Nil, s), ss, rOccur, prunable) = Nil | pruneSpine (G, (App (U, S), s), ss, rOccur, prunable) = App (pruneExp (G, (U, s), ss, rOccur, prunable), pruneSpine (G, (S, s), ss, rOccur, prunable)) | pruneSpine (G, (SClo (S, s'), s), ss, rOccur, prunable) = pruneSpine (G, (S, comp (s', s)), ss, rOccur, prunable) and pruneHead (G, BVar k, ss, rOccur, prunable) = (case (bvarSub (k, ss)) of Undef => raise Unify "Parameter dependency" | Idx k' => BVar k') | pruneHead (G, H as Const _, ss, rOccur, prunable) = H | pruneHead (G, Proj (B as Bidx k, i), ss, rOccur, pruneable) = (* blockSub (B, ss) should always be defined *) (* Fri Dec 28 10:03:12 2001 -fp !!! *) (case blockSub (B, ss) of Bidx(k') => Proj (Bidx (k'), i)) | pruneHead (G, H as Proj (LVar (r, sk, (l, t)), i), ss, rOccur, prunable) = (* claim: LVar does not need to be pruned since . |- t : Gsome *) (* so we perform only the occurs-check here as for FVars *) (* Sat Dec 8 13:39:41 2001 -fp !!! *) (* this is not true any more, Sun Dec 1 11:28:47 2002 -cs *) (* Changed from Null to G Sat Dec 7 21:58:00 2002 -fp *) ( pruneSub (G, t, id, rOccur, prunable) ; H ) | pruneHead (G, H as Skonst _, ss, rOccur, prunable) = H | pruneHead (G, H as Def _, ss, rOccur, prunable) = H | pruneHead (G, FVar (x, V, s'), ss, rOccur, prunable) = (* V does not to be pruned, since . |- V : type and s' = ^k *) (* perform occurs-check for r only *) (pruneExp (G, (V, id), id, rOccur, prunable); (* why G here? -fp !!! *) FVar (x, V, comp (s', ss))) | pruneHead (G, H as FgnConst _, ss, rOccur, prunable) = H (* pruneSub never allows pruning OUTDATED *) (* in the presence of block variables, this invariant doesn't hold any more, because substitutions do not only occur in EVars any more but also in LVars! and there pruning is allowed! Tue May 29 21:50:17 EDT 2001 -cs *) and pruneSub (G, s as Shift (n), ss, rOccur, prunable) = if n < ctxLength (G) then pruneSub (G, Dot (Idx (n+1), Shift (n+1)), ss, rOccur, prunable) else comp (s, ss) (* must be defined *) | pruneSub (G, Dot (Idx (n), s'), ss, rOccur, prunable) = (case bvarSub (n, ss) of Undef => raise Unify "Not prunable" | Ft => Dot (Ft, pruneSub (G, s', ss, rOccur, prunable))) | pruneSub (G, Dot (Exp (U), s'), ss, rOccur, prunable) = (* below my raise Unify *) Dot (Exp (pruneExp (G, (U, id), ss, rOccur, prunable)), pruneSub (G, s', ss, rOccur, prunable)) (* pruneSub (G, Dot (Undef, s), ss, rOccur) is impossible *) (* By invariant, all EVars X[s] are such that s is defined everywhere *) (* Pruning establishes and maintains this invariant *) and pruneCtx (Shift n, Null, rOccur, prunable) = Null | pruneCtx (Dot (Idx k, t), Decl (G, D), rOccur, prunable) = let val t' = comp (t, invShift) val D' = pruneDec (G, (D, id), t', rOccur, prunable) in Decl (pruneCtx (t', G, rOccur, prunable), D') end | pruneCtx (Dot (Undef, t), Decl (G, d), rOccur, prunable) = pruneCtx (t, G, rOccur, prunable) | pruneCtx (Shift n, G, rOccur, prunable) = pruneCtx (Dot (Idx (n+1), Shift (n+1)), G, rOccur, prunable) (* unifyExpW (G, (U1, s1), (U2, s2)) = () Invariant: If G |- s1 : G1 G1 |- U1 : V1 (U1,s1) in whnf and G |- s2 : G2 G2 |- U2 : V2 (U2,s2) in whnf and G |- V1 [s1] = V2 [s2] : L (for some level L) ***** or V1 = V2 = kind (needed to check type definitions) ***** added by kw Apr 5 2002 and s1, U1, s2, U2 do not contain any blockvariable indices Bidx then if there is an instantiation I : s.t. G |- U1 [s1] == U2 [s2] then instantiation is applied as effect, () returned else exception Unify is raised Other effects: EVars may be lowered constraints may be added for non-patterns *) and unifyExpW (G, Us1 as (FgnExp (_, ops), _), Us2) = (case (#unifyWith(ops) (G, EClo Us2)) of (Succeed residualL) => let fun execResidual (Assign (G, EVar(r, _, _, cnstrs), W, ss)) = let val W' = pruneExp (G, (W, id), ss, r, true) in instantiateEVar (r, W', !cnstrs) end | execResidual (Delay (U, cnstr)) = delayExp ((U, id), cnstr) in List.app execResidual residualL end | Fail => raise Unify "Foreign Expression Mismatch") | unifyExpW (G, Us1, Us2 as (FgnExp (_, ops), _)) = (case (#unifyWith(ops) (G, EClo Us1)) of (Succeed opL) => let fun execOp (Assign (G, EVar(r, _, _, cnstrs), W, ss)) = let val W' = pruneExp (G, (W, id), ss, r, true) in instantiateEVar (r, W', !cnstrs) end | execOp (Delay (U, cnstr)) = delayExp ((U, id), cnstr) in List.app execOp opL end | Fail => raise Unify "Foreign Expression Mismatch") | unifyExpW (G, (Uni (L1), _), (Uni(L2), _)) = (* L1 = L2 = type, by invariant *) (* unifyUni (L1, L2) - removed Mon Aug 24 12:18:24 1998 -fp *) () | unifyExpW (G, Us1 as (Root (H1, S1), s1), Us2 as (Root (H2, S2), s2)) = (* s1 = s2 = id by whnf *) (* order of calls critical to establish unifySpine invariant *) (case (H1, H2) of (BVar(k1), BVar(k2)) => if (k1 = k2) then unifySpine (G, (S1, s1), (S2, s2)) else raise Unify "Bound variable clash" | (Const(c1), Const(c2)) => if (c1 = c2) then unifySpine (G, (S1, s1), (S2, s2)) else raise Unify "Constant clash" | (Proj (b1, i1), Proj (b2, i2)) => if (i1 = i2) then (unifyBlock (G, b1, b2); unifySpine (G, (S1, s1), (S2, s2))) else raise Unify "Global parameter clash" | (Skonst(c1), Skonst(c2)) => if (c1 = c2) then unifySpine (G, (S1, s1), (S2, s2)) else raise Unify "Skolem constant clash" | (FVar (n1,_,_), FVar (n2,_,_)) => if (n1 = n2) then unifySpine (G, (S1, s1), (S2, s2)) else raise Unify "Free variable clash" | (Def (d1), Def (d2)) => if (d1 = d2) then (* because of strict *) unifySpine (G, (S1, s1), (S2, s2)) else unifyExpW (G, Whnf.expandDef (Us1), Whnf.expandDef (Us2)) | (Def (d1), _) => unifyExpW (G, Whnf.expandDef Us1, Us2) | (_, Def(d2)) => unifyExpW (G, Us1, Whnf.expandDef Us2) | (FgnConst (cs1, ConDec (n1, _, _, _, _, _)), FgnConst (cs2, ConDec (n2, _, _, _, _, _))) => (* we require unique string representation of external constants *) if (cs1 = cs2) andalso (n1 = n2) then () else raise Unify "Foreign Constant clash" | (FgnConst (cs1, ConDef (n1, _, _, W1, _, _)), FgnConst (cs2, ConDef (n2, _, _, V, W2, _))) => if (cs1 = cs2) andalso (n1 = n2) then () else unifyExp (G, (W1, s1), (W2, s2)) | (FgnConst (_, ConDef (_, _, _, W1, _, _)), _) => unifyExp (G, (W1, s1), Us2) | (_, FgnConst (_, ConDef (_, _, _, W2, _, _))) => unifyExp (G, Us1, (W2, s2)) | _ => raise Unify "Head mismatch") | unifyExpW (G, (Pi ((D1, _), U1), s1), (Pi ((D2, _), U2), s2)) = (unifyDec (G, (D1, s1), (D2, s2)) ; unifyExp (Decl (G, decSub (D1, s1)), (U1, dot1 s1), (U2, dot1 s2))) | unifyExpW (G, Us1 as (Pi (_, _), _), Us2 as (Root (Def _, _), _)) = unifyExpW (G, Us1, Whnf.expandDef (Us2)) | unifyExpW (G, Us1 as (Root (Def _, _), _), Us2 as (Pi (_, _), _)) = unifyExpW (G, Whnf.expandDef (Us1), Us2) | unifyExpW (G, (Lam (D1, U1), s1), (Lam (D2, U2), s2)) = (* D1[s1] = D2[s2] by invariant *) unifyExp (Decl (G, decSub (D1, s1)), (U1, dot1 s1),(U2, dot1 s2)) | unifyExpW (G, (Lam (D1, U1), s1), (U2, s2)) = (* ETA: can't occur if eta expanded *) unifyExp (Decl (G, decSub (D1, s1)), (U1, dot1 s1), (Redex (EClo (U2, shift), App (Root (BVar (1), Nil), Nil)), dot1 s2)) (* for rhs: (U2[s2])[^] 1 = U2 [s2 o ^] 1 = U2 [^ o (1. s2 o ^)] 1 = (U2 [^] 1) [1.s2 o ^] *) | unifyExpW (G, (U1, s1), (Lam (D2, U2), s2)) = (* Cannot occur if expressions are eta expanded *) unifyExp (Decl (G, decSub (D2, s2)), (Redex (EClo (U1, shift), App (Root (BVar (1), Nil), Nil)), dot1 s1), (U2, dot1 s2)) (* same reasoning holds as above *) | unifyExpW (G, Us1 as (U1 as EVar(r1, G1, V1, cnstrs1), s1), Us2 as (U2 as EVar(r2, G2, V2, cnstrs2), s2)) = (* postpone, if s1 or s2 are not patsub *) if r1 = r2 then if Whnf.isPatSub(s1) then if Whnf.isPatSub(s2) then let val s' = intersection (s1,s2) (* compute s' directly? *) val ss' = Whnf.invert s' val V1' = EClo (V1, ss') (* invertExp ((V1, id), s', ref NONE) *) val G1' = Whnf.strengthen (ss', G1) in instantiateEVar (r1, EClo (newEVar (G1', V1'), s'), !cnstrs1) end else addConstraint (cnstrs2, ref (Eqn (G, EClo Us2, EClo Us1))) else addConstraint (cnstrs1, ref (Eqn (G, EClo Us1, EClo Us2))) else if Whnf.isPatSub(s1) then let val ss1 = Whnf.invert s1 val U2' = pruneExp (G, Us2, ss1, r1, true) (* prunable set to true -cs *) in (* instantiateEVar (r1, EClo (U2, comp(s2, ss1)), !cnstrs1) *) (* invertExpW (Us2, s1, ref NONE) *) instantiateEVar (r1, U2', !cnstrs1) end else if Whnf.isPatSub(s2) then let val ss2 = Whnf.invert s2 val U1' = pruneExp (G, Us1, ss2, r2, true) in (* instantiateEVar (r2, EClo (U1, comp(s1, ss2)), !cnstr2) *) (* invertExpW (Us1, s2, ref NONE) *) instantiateEVar (r2, U1', !cnstrs2) end else let val cnstr = ref (Eqn (G, EClo Us1, EClo Us2)) in addConstraint (cnstrs1, cnstr) end | unifyExpW (G, Us1 as (EVar(r, GX, V, cnstrs), s), Us2 as (U2,s2)) = if Whnf.isPatSub(s) then let val ss = Whnf.invert s val U2' = pruneExp (G, Us2, ss, r, true) (* could raise occurs-check *) in (* instantiateEVar (r, EClo (U2, comp(s2, ss)), !cnstrs) *) (* invertExpW (Us2, s, r) *) instantiateEVar (r, U2', !cnstrs) end else addConstraint (cnstrs, ref (Eqn (G, EClo Us1, EClo Us2))) | unifyExpW (G, Us1 as (U1,s1), Us2 as (EVar (r, GX, V, cnstrs), s)) = if Whnf.isPatSub(s) then let val ss = Whnf.invert s val U1' = pruneExp (G, Us1, ss, r, true) in (* instantiateEVar (r, EClo (U1, comp(s1, ss)), !cnstrs) *) (* invertExpW (Us1, s, r) *) instantiateEVar (r, U1', !cnstrs) end else addConstraint (cnstrs, ref (Eqn (G, EClo Us1, EClo Us2))) | unifyExpW (G, Us1, Us2) = raise Unify ("Expression clash") (* covers most remaining cases *) (* the cases for EClo or Redex should not occur because of whnf invariant *) (* unifyExp (G, (U1, s1), (U2, s2)) = () as in unifyExpW, except that arguments may not be in whnf *) and unifyExp (G, Us1 as (E1,s1), Us2 as (E2,s2)) = unifyExpW (G, Whnf.whnf Us1, Whnf.whnf Us2) (* unifySpine (G, (S1, s1), (S2, s2)) = () Invariant: If G |- s1 : G1 G1 |- S1 : V1 > W1 and G |- s2 : G2 G2 |- S2 : V2 > W2 and G |- V1 [s1] = V2 [s2] : L (for some level L) and G |- W1 [s1] = W2 [s2] then if there is an instantiation I : s.t. G |- S1 [s1] == S2 [s2] then instantiation is applied as effect, () returned else exception Unify is raised Other effects: EVars may be lowered, constraints may be added for non-patterns *) and unifySpine (G, (Nil,_), (Nil,_)) = () | unifySpine (G, (SClo (S1, s1'), s1), Ss) = unifySpine (G, (S1, comp (s1', s1)), Ss) | unifySpine (G, Ss, (SClo (S2, s2'), s2)) = unifySpine (G, Ss, (S2, comp (s2', s2))) | unifySpine (G, (App (U1, S1), s1), (App (U2, S2), s2)) = (unifyExp (G, (U1, s1), (U2, s2)) ; unifySpine (G, (S1, s1), (S2, s2))) (* Nil/App or App/Nil cannot occur by typing invariants *) and unifyDec (G, (Dec(_, V1), s1), (Dec (_, V2), s2)) = unifyExp (G, (V1, s1), (V2, s2)) (* unifySub (G, s1, s2) = () Invariant: If G |- s1 : G' and G |- s2 : G' then unifySub (G, s1, s2) terminates with () iff there exists an instantiation I, such that s1 [I] = s2 [I] Remark: unifySub is used only to unify the instantiation of SOME variables *) (* conjecture: G == Null at all times *) (* Thu Dec 6 21:01:09 2001 -fp *) and unifySub (G, Shift (n1), Shift (n2)) = () (* by invariant *) | unifySub (G, Shift(n), s2 as Dot _) = unifySub (G, Dot(Idx(n+1), Shift(n+1)), s2) | unifySub (G, s1 as Dot _, Shift(m)) = unifySub (G, s1, Dot(Idx(m+1), Shift(m+1))) | unifySub (G, Dot(Ft1,s1), Dot(Ft2,s2)) = ((case (Ft1, Ft2) of (Idx (n1), Idx (n2)) => if n1 <> n2 then raise Error "SOME variables mismatch" else () | (Exp (U1), Exp (U2)) => unifyExp (G, (U1, id), (U2, id)) | (Exp (U1), Idx (n2)) => unifyExp (G, (U1, id), (Root (BVar (n2), Nil), id)) | (Idx (n1), Exp (U2)) => unifyExp (G, (Root (BVar (n1), Nil), id), (U2, id))); (* | (Undef, Undef) => | _ => false *) (* not possible because of invariant? -cs *) unifySub (G, s1, s2)) (* substitutions s1 and s2 were redundant here --- removed *) (* Sat Dec 8 11:47:12 2001 -fp !!! *) and unifyBlock (G, LVar (ref (SOME(B1)), s, _), B2) = unifyBlock (G, blockSub (B1, s), B2) | unifyBlock (G, B1, LVar (ref (SOME(B2)), s, _)) = unifyBlock (G, B1, blockSub (B2, s)) | unifyBlock (G, B1, B2) = unifyBlockW (G, B1, B2) and unifyBlockW (G, LVar (r1, Shift(k1), (l1, t1)), LVar (r2, Shift(k2), (l2, t2))) = if l1 <> l2 then raise Unify "Label clash" else if r1 = r2 then () else ( unifySub (G, t1, t2) ; (* Sat Dec 7 22:04:31 2002 -fp *) (* invariant? always k1 = k2? *) (* prune t2? Sat Dec 7 22:09:53 2002 *) if k1 <> k2 then raise Bind else () ; (* if k1 < k2 then instantiateLVar (r1, LVar(r2, Shift(k2-k1), (l2, t2))) else instantiateLVar (r2, LVar(r1, Shift (k1-k2), (l1, t1))) *) let val ss = Whnf.invert (Shift(k1)) val t2' = pruneSub (G, t2, ss, ref NONE, true) (* hack! *) in instantiateLVar (r1, LVar(r2, Shift(0), (l2, t2'))) (* 0 = k2-k1 *) end ) | unifyBlockW (G, LVar (r1, s1, (l1, t1)), B2) = (r1 := SOME (blockSub (B2, Whnf.invert s1)) ; ()) (* -- ABP *) | unifyBlockW (G, B1, LVar (r2, s2, (l2, t2))) = (r2 := SOME (blockSub (B1, Whnf.invert s2)) ; ()) (* -- ABP *) (* | unifyBlockW (G, LVar (r1, Shift(k1), (l1, t1)), Bidx i2) = (r1 := SOME (Bidx (i2 -k1)) ; ()) (* -- ABP *) | unifyBlockW (G, Bidx i1, LVar (r2, Shift(k2), (l2, t2))) = (r2 := SOME (Bidx (i1 -k2)) ; ()) (* -- ABP *) *) (* How can the next case arise? *) (* Sat Dec 8 11:49:16 2001 -fp !!! *) | unifyBlockW (G, Bidx (n1), (Bidx (n2))) = if n1 <> n2 then raise Unify "Block index clash" else () (* | unifyBlock (LVar (r1, _, _), B as Bidx _) = instantiate (r1, B) | unifyBlock (B as Bidx _, LVar (r2, _, _)) = This is still difficult --- B must make sense in the context of the LVar Shall we use the inverse of a pattern substitution? Or postpone as a constraint if pattern substitution does not exist? Sun Dec 1 11:33:13 2002 -cs *) fun unify1W (G, Us1, Us2) = (unifyExpW (G, Us1, Us2); awakeCnstr (nextCnstr ())) and unify1 (G, Us1, Us2) = (unifyExp (G, Us1, Us2); awakeCnstr (nextCnstr ())) and awakeCnstr (NONE) = () | awakeCnstr (SOME(ref Solved)) = awakeCnstr (nextCnstr ()) | awakeCnstr (SOME(cnstr as ref (Eqn (G, U1, U2)))) = (solveConstraint cnstr; unify1 (G, (U1, id), (U2, id))) | awakeCnstr (SOME(ref (FgnCnstr (cs, ops)))) = if (#awake(ops)()) then () else raise Unify "Foreign constraint violated" fun unifyW (G, Us1, Us2) = (resetAwakenCnstrs (); unify1W (G, Us1, Us2)) fun unify (G, Us1, Us2) = (resetAwakenCnstrs (); unify1 (G, Us1, Us2)) in type unifTrail = unifTrail val reset = reset val mark = mark val unwind = unwind val suspend = suspend val resume = resume val delay = delayExp val instantiateEVar = instantiateEVar val instantiateLVar = instantiateLVar val addConstraint = addConstraint val solveConstraint = solveConstraint val intersection = intersection val unifyW = unifyW val unify = unify val unifyBlock = unifyBlock fun invertible (G, Us, ss, rOccurr) = (pruneExp (G, Us, ss, rOccurr, false); true) handle Unify _ => false fun unifiable (G, Us1, Us2) = (unify (G, Us1, Us2); true) handle Unify msg => false fun unifiable' (G, Us1, Us2) = (unify (G, Us1, Us2); NONE) handle Unify(msg) => SOME(msg) end end; (* functor Unify *)