--- /dev/null
+\begin{code}
+module Unify (
+ -- Matching and unification
+ matchTys, matchTyX, matchTysX,
+ unifyTys, unifyTysX,
+
+ tcRefineTys, tcMatchTys, tcMatchPreds, coreRefineTys,
+
+ -- Re-export
+ MaybeErr(..)
+ ) where
+
+#include "HsVersions.h"
+
+import Var ( Var, TyVar, tyVarKind )
+import VarEnv
+import VarSet
+import Kind ( isSubKind )
+import Type ( predTypeRep, newTypeRep, typeKind,
+ tyVarsOfType, tyVarsOfTypes,
+ TvSubstEnv, TvSubst(..), substTy )
+import TypeRep ( Type(..), PredType(..), funTyCon )
+import Util ( snocView )
+import ErrUtils ( Message )
+import Outputable
+import Maybes
+\end{code}
+
+
+%************************************************************************
+%* *
+ External interface
+%* *
+%************************************************************************
+
+\begin{code}
+----------------------------
+tcRefineTys, tcMatchTys
+ :: [TyVar] -- Try to unify these
+ -> TvSubstEnv -- Not idempotent
+ -> [Type] -> [Type]
+ -> MaybeErr TvSubstEnv Message -- Not idempotent
+-- This one is used by the type checker. Neither the input nor result
+-- substitition is idempotent
+tcRefineTys ex_tvs subst tys1 tys2
+ = initUM (tryToBind (mkVarSet ex_tvs)) (unify_tys Src subst tys1 tys2)
+
+tcMatchTys ex_tvs subst tys1 tys2
+ = initUM (bindOnly (mkVarSet ex_tvs)) (unify_tys Src subst tys1 tys2)
+
+tcMatchPreds
+ :: [TyVar] -- Bind these
+ -> [PredType] -> [PredType]
+ -> Maybe TvSubstEnv
+tcMatchPreds tvs preds1 preds2
+ = maybeErrToMaybe $ initUM (bindOnly (mkVarSet tvs)) $
+ unify_preds Src emptyVarEnv preds1 preds2
+
+----------------------------
+coreRefineTys :: [TyVar] -- Try to unify these
+ -> TvSubst -- A full-blown apply-once substitition
+ -> Type -- A fixed point of the incoming substitution
+ -> Type
+ -> Maybe TvSubstEnv -- In-scope set is unaffected
+-- Used by Core Lint and the simplifier. Takes a full apply-once substitution.
+-- The incoming substitution's in-scope set should mention all the variables free
+-- in the incoming types
+coreRefineTys ex_tvs subst@(TvSubst in_scope orig_env) ty1 ty2
+ = maybeErrToMaybe $ initUM (tryToBind (mkVarSet ex_tvs)) $
+ do { -- Apply the input substitution; nothing int ty2
+ let ty1' = substTy subst ty1
+ -- Run the unifier, starting with an empty env
+ ; extra_env <- unify Src emptyTvSubstEnv ty1' ty2
+
+ -- Find the fixed point of the resulting non-idempotent
+ -- substitution, and apply it to the
+ ; let extra_subst = TvSubst in_scope extra_env_fixpt
+ extra_env_fixpt = mapVarEnv (substTy extra_subst) extra_env
+ orig_env' = mapVarEnv (substTy extra_subst) orig_env
+ ; return (orig_env' `plusVarEnv` extra_env_fixpt) }
+
+
+----------------------------
+matchTys :: TyVarSet -- Template tyvars
+ -> [Type] -- Template
+ -> [Type] -- Target
+ -> Maybe TvSubstEnv -- Idempotent, because when matching
+ -- the range and domain are distinct
+
+-- PRE-CONDITION for matching: template variables are not free in the target
+
+matchTys tmpls tys1 tys2
+ = ASSERT2( not (intersectsVarSet tmpls (tyVarsOfTypes tys2)),
+ ppr tmpls $$ ppr tys1 $$ ppr tys2 )
+ maybeErrToMaybe $ initUM (bindOnly tmpls)
+ (unify_tys Src emptyTvSubstEnv tys1 tys2)
+
+matchTyX :: TyVarSet -- Template tyvars
+ -> TvSubstEnv -- Idempotent substitution to extend
+ -> Type -- Template
+ -> Type -- Target
+ -> Maybe TvSubstEnv -- Idempotent
+
+matchTyX tmpls env ty1 ty2
+ = ASSERT( not (intersectsVarSet tmpls (tyVarsOfType ty2)) )
+ maybeErrToMaybe $ initUM (bindOnly tmpls)
+ (unify Src env ty1 ty2)
+
+matchTysX :: TyVarSet -- Template tyvars
+ -> TvSubstEnv -- Idempotent substitution to extend
+ -> [Type] -- Template
+ -> [Type] -- Target
+ -> Maybe TvSubstEnv -- Idempotent
+
+matchTysX tmpls env tys1 tys2
+ = ASSERT( not (intersectsVarSet tmpls (tyVarsOfTypes tys2)) )
+ maybeErrToMaybe $ initUM (bindOnly tmpls)
+ (unify_tys Src env tys1 tys2)
+
+
+----------------------------
+unifyTys :: TyVarSet -> [Type] -> [Type] -> Maybe TvSubstEnv
+unifyTys bind_these tys1 tys2
+ = maybeErrToMaybe $ initUM (bindOnly bind_these) $
+ unify_tys Src emptyTvSubstEnv tys1 tys2
+
+unifyTysX :: TyVarSet -> TvSubstEnv -> [Type] -> [Type] -> Maybe TvSubstEnv
+unifyTysX bind_these subst tys1 tys2
+ = maybeErrToMaybe $ initUM (bindOnly bind_these) $
+ unify_tys Src subst tys1 tys2
+
+----------------------------
+tryToBind, bindOnly :: TyVarSet -> TyVar -> BindFlag
+tryToBind tv_set tv | tv `elemVarSet` tv_set = BindMe
+ | otherwise = AvoidMe
+
+bindOnly tv_set tv | tv `elemVarSet` tv_set = BindMe
+ | otherwise = DontBindMe
+
+emptyTvSubstEnv :: TvSubstEnv
+emptyTvSubstEnv = emptyVarEnv
+\end{code}
+
+
+%************************************************************************
+%* *
+ The workhorse
+%* *
+%************************************************************************
+
+\begin{code}
+unify :: SrcFlag -- True, unifying source types, false core types.
+ -> TvSubstEnv -- An existing substitution to extend
+ -> Type -> Type -- Types to be unified
+ -> UM TvSubstEnv -- Just the extended substitution,
+ -- Nothing if unification failed
+-- We do not require the incoming substitution to be idempotent,
+-- nor guarantee that the outgoing one is. That's fixed up by
+-- the wrappers.
+
+-- ToDo: remove debugging junk
+unify s subst ty1 ty2 = -- pprTrace "unify" (ppr subst <+> pprParendType ty1 <+> pprParendType ty2) $
+ unify_ s subst ty1 ty2
+
+-- Look through NoteTy in the obvious fashion
+unify_ s subst (NoteTy _ ty1) ty2 = unify s subst ty1 ty2
+unify_ s subst ty1 (NoteTy _ ty2) = unify s subst ty1 ty2
+
+-- In Core mode, look through NewTcApps and Preds
+unify_ Core subst (NewTcApp tc tys) ty2 = unify Core subst (newTypeRep tc tys) ty2
+unify_ Core subst ty1 (NewTcApp tc tys) = unify Core subst ty1 (newTypeRep tc tys)
+
+unify_ Core subst (PredTy p) ty2 = unify Core subst (predTypeRep p) ty2
+unify_ Core subst ty1 (PredTy p) = unify Core subst ty1 (predTypeRep p)
+
+-- From now on, any NewTcApps/Preds should be taken at face value
+
+unify_ s subst (TyVarTy tv1) ty2 = uVar s False subst tv1 ty2
+unify_ s subst ty1 (TyVarTy tv2) = uVar s True subst tv2 ty1
+
+unify_ s subst (PredTy p1) (PredTy p2) = unify_pred s subst p1 p2
+
+unify_ s subst t1@(TyConApp tyc1 tys1) t2@(TyConApp tyc2 tys2)
+ | tyc1 == tyc2 = unify_tys s subst tys1 tys2
+unify_ Src subst t1@(NewTcApp tc1 tys1) t2@(NewTcApp tc2 tys2)
+ | tc1 == tc2 = unify_tys Src subst tys1 tys2
+unify_ s subst (FunTy ty1a ty1b) (FunTy ty2a ty2b)
+ = do { subst' <- unify s subst ty1a ty2a
+ ; unify s subst' ty1b ty2b }
+
+ -- Applications need a bit of care!
+ -- They can match FunTy and TyConApp, so use splitAppTy_maybe
+ -- NB: we've already dealt with type variables and Notes,
+ -- so if one type is an App the other one jolly well better be too
+unify_ s subst (AppTy ty1a ty1b) ty2
+ | Just (ty2a, ty2b) <- unifySplitAppTy_maybe ty2
+ = do { subst' <- unify s subst ty1a ty2a
+ ; unify s subst' ty1b ty2b }
+
+unify_ s subst ty1 (AppTy ty2a ty2b)
+ | Just (ty1a, ty1b) <- unifySplitAppTy_maybe ty1
+ = do { subst' <- unify s subst ty1a ty2a
+ ; unify s subst' ty1b ty2b }
+
+unify_ s subst ty1 ty2 = failWith (misMatch ty1 ty2)
+
+------------------------------
+unify_pred s subst (ClassP c1 tys1) (ClassP c2 tys2)
+ | c1 == c2 = unify_tys s subst tys1 tys2
+unify_pred s subst (IParam n1 t1) (IParam n2 t2)
+ | n1 == n2 = unify s subst t1 t2
+
+------------------------------
+unifySplitAppTy_maybe :: Type -> Maybe (Type,Type)
+-- NoteTy is already dealt with; take NewTcApps at face value
+unifySplitAppTy_maybe (FunTy ty1 ty2) = Just (TyConApp funTyCon [ty1], ty2)
+unifySplitAppTy_maybe (AppTy ty1 ty2) = Just (ty1, ty2)
+unifySplitAppTy_maybe (TyConApp tc tys) = case snocView tys of
+ Just (tys', ty') -> Just (TyConApp tc tys', ty')
+ Nothing -> Nothing
+unifySplitAppTy_maybe (NewTcApp tc tys) = case snocView tys of
+ Just (tys', ty') -> Just (NewTcApp tc tys', ty')
+ Nothing -> Nothing
+unifySplitAppTy_maybe other = Nothing
+
+------------------------------
+unify_tys s = unifyList (unify s)
+
+unify_preds :: SrcFlag -> TvSubstEnv -> [PredType] -> [PredType] -> UM TvSubstEnv
+unify_preds s = unifyList (unify_pred s)
+
+unifyList :: Outputable a
+ => (TvSubstEnv -> a -> a -> UM TvSubstEnv)
+ -> TvSubstEnv -> [a] -> [a] -> UM TvSubstEnv
+unifyList unifier subst orig_xs orig_ys
+ = go subst orig_xs orig_ys
+ where
+ go subst [] [] = return subst
+ go subst (x:xs) (y:ys) = do { subst' <- unifier subst x y
+ ; go subst' xs ys }
+ go subst _ _ = failWith (lengthMisMatch orig_xs orig_ys)
+
+------------------------------
+uVar :: SrcFlag -- True, unifying source types, false core types.
+ -> Bool -- Swapped
+ -> TvSubstEnv -- An existing substitution to extend
+ -> TyVar -- Type variable to be unified
+ -> Type -- with this type
+ -> UM TvSubstEnv
+
+uVar s swap subst tv1 ty
+ = -- check to see whether tv1 is refined
+ case (lookupVarEnv subst tv1) of
+ -- yes, call back into unify'
+ Just ty' | swap -> unify s subst ty ty'
+ | otherwise -> unify s subst ty' ty
+ -- No, continue
+ Nothing -> uUnrefined subst tv1 ty
+
+
+uUnrefined :: TvSubstEnv -- An existing substitution to extend
+ -> TyVar -- Type variable to be unified
+ -> Type -- with this type
+ -> UM TvSubstEnv
+
+-- We know that tv1 isn't refined
+uUnrefined subst tv1 ty2@(TyVarTy tv2)
+ | tv1 == tv2 -- Same, do nothing
+ = return subst
+
+ -- Check to see whether tv2 is refined
+ | Just ty' <- lookupVarEnv subst tv2
+ = uUnrefined subst tv1 ty'
+
+ -- So both are unrefined; next, see if the kinds force the direction
+ | k1 == k2 -- Can update either; so check the bind-flags
+ = do { b1 <- tvBindFlag tv1
+ ; b2 <- tvBindFlag tv2
+ ; case (b1,b2) of
+ (DontBindMe, DontBindMe) -> failWith (misMatch ty1 ty2)
+ (DontBindMe, _) -> bindTv subst tv2 ty1
+ (BindMe, _) -> bindTv subst tv1 ty2
+ (AvoidMe, BindMe) -> bindTv subst tv2 ty1
+ (AvoidMe, _) -> bindTv subst tv1 ty2
+ }
+
+ | k1 `isSubKind` k2 -- Must update tv2
+ = do { b2 <- tvBindFlag tv2
+ ; case b2 of
+ DontBindMe -> failWith (misMatch ty1 ty2)
+ other -> bindTv subst tv2 ty1
+ }
+
+ | k2 `isSubKind` k1 -- Must update tv1
+ = do { b1 <- tvBindFlag tv1
+ ; case b1 of
+ DontBindMe -> failWith (misMatch ty1 ty2)
+ other -> bindTv subst tv1 ty2
+ }
+
+ | otherwise = failWith (kindMisMatch tv1 ty2)
+ where
+ ty1 = TyVarTy tv1
+ k1 = tyVarKind tv1
+ k2 = tyVarKind tv2
+
+uUnrefined subst tv1 ty2 -- ty2 is not a type variable
+ -- Do occurs check...
+ | tv1 `elemVarSet` substTvSet subst (tyVarsOfType ty2)
+ = failWith (occursCheck tv1 ty2)
+ -- And a kind check...
+ | k2 `isSubKind` k1
+ = do { b1 <- tvBindFlag tv1
+ ; case b1 of -- And check that tv1 is bindable
+ DontBindMe -> failWith (misMatch ty1 ty2)
+ other -> bindTv subst tv1 ty2
+ }
+ | otherwise
+ = pprTrace "kind" (ppr tv1 <+> ppr k1 $$ ppr ty2 <+> ppr k2) $
+ failWith (kindMisMatch tv1 ty2)
+ where
+ ty1 = TyVarTy tv1
+ k1 = tyVarKind tv1
+ k2 = typeKind ty2
+
+substTvSet :: TvSubstEnv -> TyVarSet -> TyVarSet
+-- Apply the non-idempotent substitution to a set of type variables,
+-- remembering that the substitution isn't necessarily idempotent
+substTvSet subst tvs
+ = foldVarSet (unionVarSet . get) emptyVarSet tvs
+ where
+ get tv = case lookupVarEnv subst tv of
+ Nothing -> unitVarSet tv
+ Just ty -> substTvSet subst (tyVarsOfType ty)
+
+bindTv subst tv ty = return (extendVarEnv subst tv ty)
+\end{code}
+
+%************************************************************************
+%* *
+ Unification monad
+%* *
+%************************************************************************
+
+\begin{code}
+data SrcFlag = Src | Core -- Unifying at the source level, or core level?
+
+data BindFlag = BindMe | AvoidMe | DontBindMe
+
+isCore Core = True
+isCore Src = False
+
+newtype UM a = UM { unUM :: (TyVar -> BindFlag)
+ -> MaybeErr a Message }
+
+instance Monad UM where
+ return a = UM (\tvs -> Succeeded a)
+ fail s = UM (\tvs -> Failed (text s))
+ m >>= k = UM (\tvs -> case unUM m tvs of
+ Failed err -> Failed err
+ Succeeded v -> unUM (k v) tvs)
+
+initUM :: (TyVar -> BindFlag) -> UM a -> MaybeErr a Message
+initUM badtvs um = unUM um badtvs
+
+tvBindFlag :: TyVar -> UM BindFlag
+tvBindFlag tv = UM (\tv_fn -> Succeeded (tv_fn tv))
+
+failWith :: Message -> UM a
+failWith msg = UM (\tv_fn -> Failed msg)
+
+maybeErrToMaybe :: MaybeErr succ fail -> Maybe succ
+maybeErrToMaybe (Succeeded a) = Just a
+maybeErrToMaybe (Failed m) = Nothing
+\end{code}
+
+
+%************************************************************************
+%* *
+ Error reporting
+ We go to a lot more trouble to tidy the types
+ in TcUnify. Maybe we'll end up having to do that
+ here too, but I'll leave it for now.
+%* *
+%************************************************************************
+
+\begin{code}
+misMatch t1 t2
+ = ptext SLIT("Can't match types") <+> quotes (ppr t1) <+>
+ ptext SLIT("and") <+> quotes (ppr t2)
+
+lengthMisMatch tys1 tys2
+ = sep [ptext SLIT("Can't match unequal length lists"),
+ nest 2 (ppr tys1), nest 2 (ppr tys2) ]
+
+kindMisMatch tv1 t2
+ = vcat [ptext SLIT("Can't match kinds") <+> quotes (ppr (tyVarKind tv1)) <+>
+ ptext SLIT("and") <+> quotes (ppr (typeKind t2)),
+ ptext SLIT("when matching") <+> quotes (ppr tv1) <+>
+ ptext SLIT("with") <+> quotes (ppr t2)]
+
+occursCheck tv ty
+ = hang (ptext SLIT("Can't construct the infinite type"))
+ 2 (ppr tv <+> equals <+> ppr ty)
+\end{code}
\ No newline at end of file
projects / ghc-hetmet.git / blobdiff