\begin{code}
module Unify (
-- Matching and unification
- matchTys, matchTyX, matchTysX,
- unifyTys, unifyTysX,
+ tcMatchTys, tcMatchTyX, ruleMatchTyX, tcMatchPreds, MatchEnv(..),
- tcRefineTys, tcMatchTys, tcMatchPreds, coreRefineTys,
+ tcUnifyTys,
+
+ gadtRefineTys, BindFlag(..),
+
+ coreRefineTys, TypeRefinement,
-- Re-export
MaybeErr(..)
import VarEnv
import VarSet
import Kind ( isSubKind )
-import Type ( predTypeRep, newTypeRep, typeKind,
- tyVarsOfType, tyVarsOfTypes,
- TvSubstEnv, TvSubst(..), substTy )
+import Type ( typeKind, tyVarsOfType, tyVarsOfTypes, tyVarsOfTheta, mkTyVarTys,
+ TvSubstEnv, emptyTvSubstEnv, TvSubst(..), substTy, tcEqTypeX,
+ mkOpenTvSubst, tcView )
import TypeRep ( Type(..), PredType(..), funTyCon )
+import DataCon ( DataCon, dataConInstResTy )
import Util ( snocView )
import ErrUtils ( Message )
import Outputable
%************************************************************************
%* *
- External interface
+ Matching
%* *
%************************************************************************
-\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
+Matching is much tricker than you might think.
-----------------------------
-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) }
-
+1. The substitution we generate binds the *template type variables*
+ which are given to us explicitly.
-----------------------------
-matchTys :: TyVarSet -- Template tyvars
+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
+
+tcMatchTys :: TyVarSet -- Template tyvars
-> [Type] -- Template
-> [Type] -- Target
- -> Maybe TvSubstEnv -- Idempotent, because when matching
- -- the range and domain are distinct
+ -> Maybe TvSubst -- One-shot; in principle the template
+ -- variables could be free in the target
--- PRE-CONDITION for matching: template variables are not free in the target
+tcMatchTys tmpls tys1 tys2
+ = case match_tys menv emptyTvSubstEnv tys1 tys2 of
+ Just subst_env -> Just (TvSubst in_scope subst_env)
+ Nothing -> Nothing
+ where
+ menv = ME { me_tmpls = tmpls, me_env = mkRnEnv2 in_scope }
+ in_scope = mkInScopeSet (tmpls `unionVarSet` tyVarsOfTypes tys2)
+ -- We're assuming that all the interesting
+ -- tyvars in tys1 are in tmpls
+
+-- This is similar, but extends a substitution
+tcMatchTyX :: TyVarSet -- Template tyvars
+ -> TvSubst -- Substitution to extend
+ -> Type -- Template
+ -> Type -- Target
+ -> Maybe TvSubst
+tcMatchTyX tmpls (TvSubst in_scope subst_env) ty1 ty2
+ = case match menv subst_env ty1 ty2 of
+ Just subst_env -> Just (TvSubst in_scope subst_env)
+ Nothing -> Nothing
+ where
+ menv = ME {me_tmpls = tmpls, me_env = mkRnEnv2 in_scope}
-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)
+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 :: TyVarSet -- Template tyvars
- -> TvSubstEnv -- Idempotent substitution to extend
+-- This one is called from the expression matcher, which already has a MatchEnv in hand
+ruleMatchTyX :: MatchEnv
+ -> TvSubstEnv -- Substitution to extend
-> Type -- Template
-> Type -- Target
- -> Maybe TvSubstEnv -- Idempotent
+ -> Maybe TvSubstEnv
-matchTyX tmpls env ty1 ty2
- = ASSERT( not (intersectsVarSet tmpls (tyVarsOfType ty2)) )
- maybeErrToMaybe $ initUM (bindOnly tmpls)
- (unify Src env ty1 ty2)
+ruleMatchTyX menv subst ty1 ty2 = match menv subst ty1 ty2 -- Rename for export
+\end{code}
-matchTysX :: TyVarSet -- Template tyvars
- -> TvSubstEnv -- Idempotent substitution to extend
- -> [Type] -- Template
- -> [Type] -- Target
- -> Maybe TvSubstEnv -- Idempotent
+Now the internals of matching
-matchTysX tmpls env tys1 tys2
- = ASSERT( not (intersectsVarSet tmpls (tyVarsOfTypes tys2)) )
- maybeErrToMaybe $ initUM (bindOnly tmpls)
- (unify_tys Src env tys1 tys2)
+\begin{code}
+match :: MatchEnv -- For the most 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 ty1 ty2 | Just ty1' <- tcView ty1 = match menv subst ty1' ty2
+match menv subst ty1 ty2 | Just ty2' <- tcView 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
+ | not (typeKind ty2 `isSubKind` tyVarKind tv1)
+ -> Nothing -- Kind mis-match
+ | 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}
-----------------------------
-unifyTys :: TyVarSet -> [Type] -> [Type] -> Maybe TvSubstEnv
-unifyTys bind_these tys1 tys2
- = maybeErrToMaybe $ initUM (bindOnly bind_these) $
- unify_tys Src emptyTvSubstEnv tys1 tys2
+%************************************************************************
+%* *
+ Unification
+%* *
+%************************************************************************
+
+\begin{code}
+tcUnifyTys :: (TyVar -> BindFlag)
+ -> [Type] -> [Type]
+ -> Maybe TvSubst -- A regular one-shot substitution
+-- The two types may have common type variables, and indeed do so in the
+-- second call to tcUnifyTys in FunDeps.checkClsFD
+tcUnifyTys bind_fn tys1 tys2
+ = maybeErrToMaybe $ initUM bind_fn $
+ do { subst_env <- unify_tys emptyTvSubstEnv tys1 tys2
+
+ -- Find the fixed point of the resulting non-idempotent substitution
+ ; let in_scope = mkInScopeSet (tvs1 `unionVarSet` tvs2)
+ subst = TvSubst in_scope subst_env_fixpt
+ subst_env_fixpt = mapVarEnv (substTy subst) subst_env
+ ; return subst }
+ where
+ tvs1 = tyVarsOfTypes tys1
+ tvs2 = tyVarsOfTypes 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
+----------------------------
+coreRefineTys :: DataCon -> [TyVar] -- Case pattern (con tv1 .. tvn ...)
+ -> Type -- Type of scrutinee
+ -> Maybe TypeRefinement
+
+type TypeRefinement = (TvSubstEnv, Bool)
+ -- The Bool is True iff all the bindings in the
+ -- env are for the pattern type variables
+ -- In this case, there is no type refinement
+ -- for already-in-scope type variables
+
+-- Used by Core Lint and the simplifier.
+coreRefineTys con tvs scrut_ty
+ = maybeErrToMaybe $ initUM (tryToBind tv_set) $
+ do { -- Run the unifier, starting with an empty env
+ ; subst_env <- unify emptyTvSubstEnv pat_res_ty scrut_ty
+
+ -- Find the fixed point of the resulting non-idempotent substitution
+ ; let subst = mkOpenTvSubst subst_env_fixpt
+ subst_env_fixpt = mapVarEnv (substTy subst) subst_env
+
+ ; return (subst_env_fixpt, all_bound_here subst_env) }
+ where
+ pat_res_ty = dataConInstResTy con (mkTyVarTys tvs)
+
+ -- 'tvs' are the tyvars bound by the pattern
+ tv_set = mkVarSet tvs
+ all_bound_here env = all bound_here (varEnvKeys env)
+ bound_here uniq = elemVarSetByKey uniq tv_set
+
+-- This version is used by the type checker
+gadtRefineTys :: TvSubst
+ -> DataCon -> [TyVar]
+ -> [Type] -> [Type]
+ -> MaybeErr Message (TvSubst, Bool)
+-- The bool is True <=> the only *new* bindings are for pat_tvs
+
+gadtRefineTys (TvSubst in_scope env1) con pat_tvs pat_tys ctxt_tys
+ = initUM (tryToBind tv_set) $
+ do { -- Run the unifier, starting with an empty env
+ ; env2 <- unify_tys env1 pat_tys ctxt_tys
+
+ -- Find the fixed point of the resulting non-idempotent substitution
+ ; let subst2 = TvSubst in_scope subst_env_fixpt
+ subst_env_fixpt = mapVarEnv (substTy subst2) env2
+
+ ; return (subst2, all_bound_here env2) }
+ where
+ -- 'tvs' are the tyvars bound by the pattern
+ tv_set = mkVarSet pat_tvs
+ all_bound_here env = all bound_here (varEnvKeys env)
+ bound_here uniq = elemVarEnvByKey uniq env1 || elemVarSetByKey uniq tv_set
+ -- The bool is True <=> the only *new* bindings are for pat_tvs
----------------------------
-tryToBind, bindOnly :: TyVarSet -> TyVar -> BindFlag
+tryToBind :: 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}
%************************************************************************
\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.
--- 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
+-- Respects newtypes, PredTypes
--- 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 subst ty1 ty2 = -- pprTrace "unify" (ppr subst <+> pprParendType ty1 <+> pprParendType ty2) $
+ unify_ subst ty1 ty2
-unify_ Core subst (PredTy p) ty2 = unify Core subst (predTypeRep p) ty2
-unify_ Core subst ty1 (PredTy p) = unify Core subst ty1 (predTypeRep p)
+-- in unify_, any NewTcApps/Preds should be taken at face value
+unify_ subst (TyVarTy tv1) ty2 = uVar False subst tv1 ty2
+unify_ subst ty1 (TyVarTy tv2) = uVar True subst tv2 ty1
--- From now on, any NewTcApps/Preds should be taken at face value
+unify_ subst ty1 ty2 | Just ty1' <- tcView ty1 = unify subst ty1' ty2
+unify_ subst ty1 ty2 | Just ty2' <- tcView ty2 = unify subst ty1 ty2'
-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 (PredTy p1) (PredTy p2) = unify_pred subst p1 p2
-unify_ s subst (PredTy p1) (PredTy p2) = unify_pred s subst p1 p2
+unify_ subst t1@(TyConApp tyc1 tys1) t2@(TyConApp tyc2 tys2)
+ | tyc1 == tyc2 = unify_tys subst tys1 tys2
-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 }
+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 (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)
+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
- = -- check to see whether tv1 is refined
+uVar swap subst tv1 ty
+ = -- Check to see whether tv1 is refined by the substitution
case (lookupVarEnv subst tv1) of
- -- yes, call back into unify'
- Just ty' | swap -> unify s subst ty ty'
- | otherwise -> unify s subst ty' ty
+ -- Yes, call back into unify'
+ Just ty' | swap -> unify subst ty ty'
+ | otherwise -> unify subst ty' ty
-- No, continue
- Nothing -> uUnrefined subst tv1 ty
+ Nothing -> uUnrefined subst tv1 ty ty
uUnrefined :: TvSubstEnv -- An existing substitution to extend
-> TyVar -- Type variable to be unified
-> Type -- with this type
+ -> Type -- (de-noted version)
-> UM TvSubstEnv
-- We know that tv1 isn't refined
-uUnrefined subst tv1 ty2@(TyVarTy tv2)
- | tv1 == tv2 -- Same, do nothing
+
+uUnrefined subst tv1 ty2 ty2'
+ | Just ty2'' <- tcView ty2'
+ = uUnrefined subst tv1 ty2 ty2'' -- Unwrap synonyms
+ -- This is essential, in case we have
+ -- type Foo a = a
+ -- and then unify a :=: Foo a
+
+uUnrefined subst tv1 ty2 (TyVarTy tv2)
+ | tv1 == tv2 -- Same type variable
= return subst
-- Check to see whether tv2 is refined
| Just ty' <- lookupVarEnv subst tv2
- = uUnrefined subst tv1 ty'
+ = uUnrefined subst tv1 ty' 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
- }
+ (BindMe, _) -> bind 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
- }
+ (AvoidMe, BindMe) -> bind tv2 ty1
+ (AvoidMe, _) -> bind tv1 ty2
- | k2 `isSubKind` k1 -- Must update tv1
- = do { b1 <- tvBindFlag tv1
- ; case b1 of
- DontBindMe -> failWith (misMatch ty1 ty2)
- other -> bindTv subst tv1 ty2
+ (WildCard, WildCard) -> return subst
+ (WildCard, Skolem) -> return subst
+ (WildCard, _) -> bind tv2 ty1
+
+ (Skolem, WildCard) -> return subst
+ (Skolem, Skolem) -> failWith (misMatch ty1 ty2)
+ (Skolem, _) -> bind tv2 ty1
}
+ | k1 `isSubKind` k2 = bindTv subst tv2 ty1 -- Must update tv2
+ | k2 `isSubKind` k1 = bindTv subst tv1 ty2 -- Must update tv1
+
| otherwise = failWith (kindMisMatch tv1 ty2)
where
ty1 = TyVarTy tv1
k1 = tyVarKind tv1
k2 = tyVarKind tv2
+ bind tv ty = return (extendVarEnv subst tv ty)
-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
- }
+uUnrefined subst tv1 ty2 ty2' -- ty2 is not a type variable
+ | tv1 `elemVarSet` substTvSet subst (tyVarsOfType ty2')
+ = failWith (occursCheck tv1 ty2) -- Occurs check
+ | not (k2 `isSubKind` k1)
+ = failWith (kindMisMatch tv1 ty2) -- Kind check
| otherwise
- = pprTrace "kind" (ppr tv1 <+> ppr k1 $$ ppr ty2 <+> ppr k2) $
- failWith (kindMisMatch tv1 ty2)
+ = bindTv subst tv1 ty2 -- Bind tyvar to the synonym if poss
where
- ty1 = TyVarTy tv1
k1 = tyVarKind tv1
- k2 = typeKind ty2
+ k2 = typeKind ty2'
substTvSet :: TvSubstEnv -> TyVarSet -> TyVarSet
-- Apply the non-idempotent substitution to a set of type variables,
Nothing -> unitVarSet tv
Just ty -> substTvSet subst (tyVarsOfType ty)
-bindTv subst tv ty = return (extendVarEnv subst tv ty)
+bindTv subst tv ty -- ty is not a type variable
+ = do { b <- tvBindFlag tv
+ ; case b of
+ Skolem -> failWith (misMatch (TyVarTy tv) ty)
+ WildCard -> return subst
+ other -> return (extendVarEnv subst tv ty)
+ }
\end{code}
%************************************************************************
%************************************************************************
\begin{code}
-data SrcFlag = Src | Core -- Unifying at the source level, or core level?
+data BindFlag
+ = BindMe -- A regular type variable
+ | AvoidMe -- Like BindMe but, given the choice, avoid binding it
-data BindFlag = BindMe | AvoidMe | DontBindMe
+ | Skolem -- This type variable is a skolem constant
+ -- Don't bind it; it only matches itself
-isCore Core = True
-isCore Src = False
+ | WildCard -- This type variable matches anything,
+ -- and does not affect the substitution
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