-- Matching and unification
tcMatchTys, tcMatchTyX, tcMatchPreds, MatchEnv(..),
- tcUnifyTys, tcUnifyTysX,
+ tcUnifyTys,
- gadtRefineTys, gadtMatchTys, coreRefineTys,
+ gadtRefineTys, BindFlag(..),
+
+ coreRefineTys,
-- Re-export
MaybeErr(..)
#include "HsVersions.h"
-import Type ( pprParendType )
import Var ( Var, TyVar, tyVarKind )
import VarEnv
import VarSet
import Kind ( isSubKind )
import Type ( typeKind, tyVarsOfType, tyVarsOfTypes, tyVarsOfTheta,
- TvSubstEnv, TvSubst(..), substTy, tcEqTypeX )
+ TvSubstEnv, emptyTvSubstEnv, TvSubst(..), substTy, tcEqTypeX )
import TypeRep ( Type(..), PredType(..), funTyCon )
import Util ( snocView )
import ErrUtils ( Message )
tcMatchTys :: TyVarSet -- Template tyvars
-> [Type] -- Template
-> [Type] -- Target
- -> Maybe TvSubstEnv -- One-shot; in principle the template
+ -> Maybe TvSubst -- One-shot; in principle the template
-- variables could be free in the target
tcMatchTys tmpls tys1 tys2
- = match_tys (ME { me_tmpls = tmpls, me_env = mkRnEnv2 in_scope_tyvars})
- emptyTvSubstEnv
- tys1 tys2
+ = case match_tys menv emptyTvSubstEnv tys1 tys2 of
+ Just subst_env -> Just (TvSubst in_scope subst_env)
+ Nothing -> Nothing
where
- in_scope_tyvars = mkInScopeSet (tmpls `unionVarSet` tyVarsOfTypes tys2)
+ 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
menv = ME { me_tmpls = mkVarSet tmpls, me_env = mkRnEnv2 in_scope_tyvars }
in_scope_tyvars = mkInScopeSet (tyVarsOfTheta ps1 `unionVarSet` tyVarsOfTheta ps2)
+-- This one is called from the expression matcher, which already has a MatchEnv in hand
tcMatchTyX :: MatchEnv
-> TvSubstEnv -- Substitution to extend
-> Type -- Template
Now the internals of matching
\begin{code}
-match :: MatchEnv -- For the ost part this is pushed downwards
+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
= 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)
%************************************************************************
%* *
- The workhorse
+ Unification
%* *
%************************************************************************
\begin{code}
-gadtRefineTys, gadtMatchTys
- :: [TyVar] -- Try to unify these
- -> TvSubstEnv -- Not idempotent
- -> [Type] -> [Type]
- -> MaybeErr Message TvSubstEnv -- Not idempotent
--- This one is used by the type checker. Neither the input nor result
--- substitition is idempotent
-gadtRefineTys ex_tvs subst tys1 tys2
- = initUM (tryToBind (mkVarSet ex_tvs)) (unify_tys subst tys1 tys2)
-
-gadtMatchTys ex_tvs subst tys1 tys2
- = initUM (bindOnly (mkVarSet ex_tvs)) (unify_tys subst tys1 tys2)
+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
----------------------------
-coreRefineTys :: [TyVar] -- Try to unify these
- -> TvSubst -- A full-blown apply-once substitition
+coreRefineTys :: InScopeSet -- Superset of free vars of either type
+ -> [TyVar] -- Try to unify these
-> Type -- Both types should be a fixed point
-> Type -- of the incoming substitution
-> 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
+coreRefineTys in_scope ex_tvs ty1 ty2
= maybeErrToMaybe $ initUM (tryToBind (mkVarSet ex_tvs)) $
do { -- Run the unifier, starting with an empty env
- ; extra_env <- unify emptyTvSubstEnv ty1 ty2
+ ; subst_env <- unify emptyTvSubstEnv ty1 ty2
- -- Find the fixed point of the resulting non-idempotent
- -- substitution, and apply it to the incoming substitution
- ; 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) }
+ -- Find the fixed point of the resulting non-idempotent substitution
+ ; let subst = TvSubst in_scope subst_env_fixpt
+ subst_env_fixpt = mapVarEnv (substTy subst) subst_env
+ ; return subst_env_fixpt }
----------------------------
-tcUnifyTys :: TyVarSet -> [Type] -> [Type] -> Maybe TvSubstEnv
-tcUnifyTys bind_these tys1 tys2
- = maybeErrToMaybe $ initUM (bindOnly bind_these) $
- unify_tys emptyTvSubstEnv tys1 tys2
-
-tcUnifyTysX :: TyVarSet -> TvSubstEnv -> [Type] -> [Type] -> Maybe TvSubstEnv
-tcUnifyTysX bind_these subst tys1 tys2
- = maybeErrToMaybe $ initUM (bindOnly bind_these) $
- unify_tys subst tys1 tys2
+gadtRefineTys
+ :: (TyVar -> BindFlag) -- Try to unify these
+ -> TvSubstEnv -- Not idempotent
+ -> [Type] -> [Type]
+ -> MaybeErr Message TvSubstEnv -- Not idempotent
+-- This one is used by the type checker. Neither the input nor result
+-- substitition is idempotent
+gadtRefineTys bind_fn subst tys1 tys2
+ = initUM bind_fn (unify_tys subst tys1 tys2)
----------------------------
-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}
-> UM TvSubstEnv
uVar swap subst tv1 ty
- = -- check to see whether tv1 is refined
+ = -- Check to see whether tv1 is refined by the substitution
case (lookupVarEnv subst tv1) of
- -- yes, call back into unify'
+ -- Yes, call back into unify'
Just ty' | swap -> unify subst ty ty'
| otherwise -> unify subst ty' ty
-- No, continue
= 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
- }
+ = 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
where
- ty1 = TyVarTy tv1
k1 = tyVarKind tv1
k2 = typeKind ty2
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 BindFlag = BindMe | AvoidMe | DontBindMe
+data BindFlag
+ = BindMe -- A regular type variable
+ | AvoidMe -- Like BindMe but, given the choice, avoid binding it
+
+ | Skolem -- This type variable is a skolem constant
+ -- Don't bind it; it only matches itself
+
+ | WildCard -- This type variable matches anything,
+ -- and does not affect the substitution
newtype UM a = UM { unUM :: (TyVar -> BindFlag)
-> MaybeErr Message a }
projects / ghc-hetmet.git / blobdiff