\begin{code}
module Unify (
-- Matching and unification
- matchTys, matchTyX, matchTysX,
+ matchTys, matchTyX, tcMatchPreds, MatchEnv(..),
+
unifyTys, unifyTysX,
- tcRefineTys, tcMatchTys, tcMatchPreds, coreRefineTys,
+ tcRefineTys, tcMatchTys, coreRefineTys,
-- Re-export
MaybeErr(..)
import VarEnv
import VarSet
import Kind ( isSubKind )
-import Type ( predTypeRep, typeKind,
- tyVarsOfType, tyVarsOfTypes, coreView,
- TvSubstEnv, TvSubst(..), substTy )
+import Type ( typeKind, tyVarsOfType, tyVarsOfTypes, tyVarsOfTheta,
+ TvSubstEnv, TvSubst(..), substTy, tcEqTypeX )
import TypeRep ( Type(..), PredType(..), funTyCon )
import Util ( snocView )
import ErrUtils ( Message )
%************************************************************************
%* *
- External interface
+ Matching
+%* *
+%************************************************************************
+
+
+Matching is much tricker than you might think.
+
+1. The substitution we generate binds the *template type variables*
+ which are given to us explicitly.
+
+2. We want to match in the presence of foralls;
+ e.g (forall a. t1) ~ (forall b. t2)
+
+ That is what the RnEnv2 is for; it does the alpha-renaming
+ that makes it as if a and b were the same variable.
+ Initialising the RnEnv2, so that it can generate a fresh
+ binder when necessary, entails knowing the free variables of
+ both types.
+
+3. We must be careful not to bind a template type variable to a
+ locally bound variable. E.g.
+ (forall a. x) ~ (forall b. b)
+ where x is the template type variable. Then we do not want to
+ bind x to a/b! This is a kind of occurs check.
+ The necessary locals accumulate in the RnEnv2.
+
+
+\begin{code}
+data MatchEnv
+ = ME { me_tmpls :: VarSet -- Template tyvars
+ , me_env :: RnEnv2 -- Renaming envt for nested foralls
+ } -- In-scope set includes template tyvars
+
+matchTys :: TyVarSet -- Template tyvars
+ -> [Type] -- Template
+ -> [Type] -- Target
+ -> Maybe TvSubstEnv -- One-shot; in principle the template
+ -- variables could be free in the target
+
+matchTys tmpls tys1 tys2
+ = match_tys (ME { me_tmpls = tmpls, me_env = mkRnEnv2 in_scope_tyvars})
+ emptyTvSubstEnv
+ tys1 tys2
+ where
+ in_scope_tyvars = mkInScopeSet (tmpls `unionVarSet` tyVarsOfTypes tys2)
+ -- We're assuming that all the interesting
+ -- tyvars in tys1 are in tmpls
+
+tcMatchPreds
+ :: [TyVar] -- Bind these
+ -> [PredType] -> [PredType]
+ -> Maybe TvSubstEnv
+tcMatchPreds tmpls ps1 ps2
+ = match_list (match_pred menv) emptyTvSubstEnv ps1 ps2
+ where
+ menv = ME { me_tmpls = mkVarSet tmpls, me_env = mkRnEnv2 in_scope_tyvars }
+ in_scope_tyvars = mkInScopeSet (tyVarsOfTheta ps1 `unionVarSet` tyVarsOfTheta ps2)
+
+matchTyX :: MatchEnv
+ -> TvSubstEnv -- Substitution to extend
+ -> Type -- Template
+ -> Type -- Target
+ -> Maybe TvSubstEnv
+
+matchTyX menv subst ty1 ty2 = match menv subst ty1 ty2 -- Rename for export
+\end{code}
+
+Now the internals of matching
+
+\begin{code}
+match :: MatchEnv -- For the ost part this is pushed downwards
+ -> TvSubstEnv -- Substitution so far:
+ -- Domain is subset of template tyvars
+ -- Free vars of range is subset of
+ -- in-scope set of the RnEnv2
+ -> Type -> Type -- Template and target respectively
+ -> Maybe TvSubstEnv
+-- This matcher works on source types; that is,
+-- it respects NewTypes and PredType
+
+match menv subst (NoteTy _ ty1) ty2 = match menv subst ty1 ty2
+match menv subst ty1 (NoteTy _ ty2) = match menv subst ty1 ty2
+
+match menv subst (TyVarTy tv1) ty2
+ | tv1 `elemVarSet` me_tmpls menv
+ = case lookupVarEnv subst tv1' of
+ Nothing | any (inRnEnvR rn_env) (varSetElems (tyVarsOfType ty2))
+ -> Nothing -- Occurs check
+ | otherwise
+ -> Just (extendVarEnv subst tv1 ty2)
+
+ Just ty1' | tcEqTypeX (nukeRnEnvL rn_env) ty1' ty2
+ -- ty1 has no locally-bound variables, hence nukeRnEnvL
+ -- Note tcEqType...we are doing source-type matching here
+ -> Just subst
+
+ other -> Nothing
+
+ | otherwise -- tv1 is not a template tyvar
+ = case ty2 of
+ TyVarTy tv2 | tv1' == rnOccR rn_env tv2 -> Just subst
+ other -> Nothing
+ where
+ rn_env = me_env menv
+ tv1' = rnOccL rn_env tv1
+
+match menv subst (ForAllTy tv1 ty1) (ForAllTy tv2 ty2)
+ = match menv' subst ty1 ty2
+ where -- Use the magic of rnBndr2 to go under the binders
+ menv' = menv { me_env = rnBndr2 (me_env menv) tv1 tv2 }
+
+match menv subst (PredTy p1) (PredTy p2)
+ = match_pred menv subst p1 p2
+match menv subst (TyConApp tc1 tys1) (TyConApp tc2 tys2)
+ | tc1 == tc2 = match_tys menv subst tys1 tys2
+match menv subst (FunTy ty1a ty1b) (FunTy ty2a ty2b)
+ = do { subst' <- match menv subst ty1a ty2a
+ ; match menv subst' ty1b ty2b }
+match menv subst (AppTy ty1a ty1b) ty2
+ | Just (ty2a, ty2b) <- repSplitAppTy_maybe ty2
+ = do { subst' <- match menv subst ty1a ty2a
+ ; match menv subst' ty1b ty2b }
+
+match menv subst ty1 ty2
+ = Nothing
+
+--------------
+match_tys menv subst tys1 tys2 = match_list (match menv) subst tys1 tys2
+
+--------------
+match_list :: (TvSubstEnv -> a -> a -> Maybe TvSubstEnv)
+ -> TvSubstEnv -> [a] -> [a] -> Maybe TvSubstEnv
+match_list fn subst [] [] = Just subst
+match_list fn subst (ty1:tys1) (ty2:tys2) = do { subst' <- fn subst ty1 ty2
+ ; match_list fn subst' tys1 tys2 }
+match_list fn subst tys1 tys2 = Nothing
+
+--------------
+match_pred menv subst (ClassP c1 tys1) (ClassP c2 tys2)
+ | c1 == c2 = match_tys menv subst tys1 tys2
+match_pred menv subst (IParam n1 t1) (IParam n2 t2)
+ | n1 == n2 = match menv subst t1 t2
+match_pred menv subst p1 p2 = Nothing
+\end{code}
+
+
+%************************************************************************
+%* *
+ The workhorse
%* *
%************************************************************************
\begin{code}
-----------------------------
tcRefineTys, tcMatchTys
:: [TyVar] -- Try to unify these
-> TvSubstEnv -- Not idempotent
-> [Type] -> [Type]
- -> MaybeErr TvSubstEnv Message -- Not idempotent
+ -> MaybeErr Message TvSubstEnv -- 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)
+ = initUM (tryToBind (mkVarSet ex_tvs)) (unify_tys 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
+ = initUM (bindOnly (mkVarSet ex_tvs)) (unify_tys subst tys1 tys2)
----------------------------
coreRefineTys :: [TyVar] -- Try to unify these
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
+ ; extra_env <- unify emptyTvSubstEnv ty1' ty2
-- Find the fixed point of the resulting non-idempotent
-- substitution, and apply it to the
----------------------------
-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
+ unify_tys 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
+ unify_tys subst tys1 tys2
----------------------------
tryToBind, bindOnly :: TyVarSet -> TyVar -> BindFlag
%************************************************************************
\begin{code}
-unify :: SrcFlag -- True, unifying source types, false core types.
- -> TvSubstEnv -- An existing substitution to extend
+unify :: TvSubstEnv -- An existing substitution to extend
-> Type -> Type -- Types to be unified
-> UM TvSubstEnv -- Just the extended substitution,
-- Nothing if unification failed
-- nor guarantee that the outgoing one is. That's fixed up by
-- the wrappers.
-unify s subst ty1 ty2 = -- pprTrace "unify" (ppr subst <+> pprParendType ty1 <+> pprParendType ty2) $
- unify_ s subst (rep s ty1) (rep s ty2)
-
-rep :: SrcFlag -> Type -> Type -- Strip off the clutter
-rep Src (NoteTy _ ty) = rep Src ty
-rep Core ty | Just ty' <- coreView ty = rep Core ty'
-rep s ty = ty
+unify subst ty1 ty2 = -- pprTrace "unify" (ppr subst <+> pprParendType ty1 <+> pprParendType ty2) $
+ unify_ subst ty1 ty2
-- in unify_, 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_ subst (TyVarTy tv1) ty2 = uVar False subst tv1 ty2
+unify_ subst ty1 (TyVarTy tv2) = uVar True subst tv2 ty1
-unify_ s subst (PredTy p1) (PredTy p2) = unify_pred s subst p1 p2
+unify_ subst (PredTy p1) (PredTy p2) = unify_pred subst p1 p2
-unify_ s subst t1@(TyConApp tyc1 tys1) t2@(TyConApp tyc2 tys2)
- | tyc1 == tyc2 = unify_tys s subst tys1 tys2
+unify_ subst t1@(TyConApp tyc1 tys1) t2@(TyConApp tyc2 tys2)
+ | tyc1 == tyc2 = unify_tys subst tys1 tys2
-unify_ s subst (FunTy ty1a ty1b) (FunTy ty2a ty2b)
- = do { subst' <- unify s subst ty1a ty2a
- ; unify s subst' ty1b ty2b }
+unify_ subst (FunTy ty1a ty1b) (FunTy ty2a ty2b)
+ = do { subst' <- unify subst ty1a ty2a
+ ; unify 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_ subst (AppTy ty1a ty1b) ty2
+ | Just (ty2a, ty2b) <- repSplitAppTy_maybe ty2
+ = do { subst' <- unify subst ty1a ty2a
+ ; unify 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_ subst ty1 (AppTy ty2a ty2b)
+ | Just (ty1a, ty1b) <- repSplitAppTy_maybe ty1
+ = do { subst' <- unify subst ty1a ty2a
+ ; unify subst' ty1b ty2b }
-unify_ s subst ty1 ty2 = failWith (misMatch ty1 ty2)
+unify_ 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
+unify_pred subst (ClassP c1 tys1) (ClassP c2 tys2)
+ | c1 == c2 = unify_tys subst tys1 tys2
+unify_pred subst (IParam n1 t1) (IParam n2 t2)
+ | n1 == n2 = unify subst t1 t2
+unify_pred subst p1 p2 = failWith (misMatch (PredTy p1) (PredTy p2))
------------------------------
-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 other = Nothing
-
-------------------------------
-unify_tys s = unifyList (unify s)
-
-unify_preds :: SrcFlag -> TvSubstEnv -> [PredType] -> [PredType] -> UM TvSubstEnv
-unify_preds s = unifyList (unify_pred s)
+unify_tys = unifyList unify
unifyList :: Outputable a
=> (TvSubstEnv -> a -> a -> UM TvSubstEnv)
go subst _ _ = failWith (lengthMisMatch orig_xs orig_ys)
------------------------------
-uVar :: SrcFlag -- True, unifying source types, false core types.
- -> Bool -- Swapped
+uVar :: 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
+uVar 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
+ Just ty' | swap -> unify subst ty ty'
+ | otherwise -> unify subst ty' ty
-- No, continue
Nothing -> uUnrefined subst tv1 ty
%************************************************************************
\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 }
+ -> MaybeErr Message a }
instance Monad UM where
return a = UM (\tvs -> Succeeded a)
Failed err -> Failed err
Succeeded v -> unUM (k v) tvs)
-initUM :: (TyVar -> BindFlag) -> UM a -> MaybeErr a Message
+initUM :: (TyVar -> BindFlag) -> UM a -> MaybeErr Message a
initUM badtvs um = unUM um badtvs
tvBindFlag :: TyVar -> UM BindFlag
failWith :: Message -> UM a
failWith msg = UM (\tv_fn -> Failed msg)
-maybeErrToMaybe :: MaybeErr succ fail -> Maybe succ
+maybeErrToMaybe :: MaybeErr fail succ -> Maybe succ
maybeErrToMaybe (Succeeded a) = Just a
maybeErrToMaybe (Failed m) = Nothing
+
+------------------------------
+repSplitAppTy_maybe :: Type -> Maybe (Type,Type)
+-- Like Type.splitAppTy_maybe, but any coreView stuff is already done
+repSplitAppTy_maybe (FunTy ty1 ty2) = Just (TyConApp funTyCon [ty1], ty2)
+repSplitAppTy_maybe (AppTy ty1 ty2) = Just (ty1, ty2)
+repSplitAppTy_maybe (TyConApp tc tys) = case snocView tys of
+ Just (tys', ty') -> Just (TyConApp tc tys', ty')
+ Nothing -> Nothing
+repSplitAppTy_maybe other = Nothing
\end{code}
projects / ghc-hetmet.git / blobdiff