%
\begin{code}
-{-# OPTIONS -w #-}
--- The above warning supression flag is a temporary kludge.
--- While working on this module you are encouraged to remove it and fix
--- any warnings in the module. See
--- http://hackage.haskell.org/trac/ghc/wiki/Commentary/CodingStyle#Warnings
--- for details
-
module Unify (
-- Matching of types:
-- the "tc" prefix indicates that matching always
tcMatchTy, tcMatchTys, tcMatchTyX,
ruleMatchTyX, tcMatchPreds, MatchEnv(..),
- dataConCannotMatch
+ dataConCannotMatch,
+
+ -- GADT type refinement
+ Refinement, emptyRefinement, isEmptyRefinement,
+ matchRefine, refineType, refinePred, refineResType,
+
+ -- side-effect free unification
+ tcUnifyTys, BindFlag(..)
+
) where
#include "HsVersions.h"
import DataCon
import TypeRep
import Outputable
+import ErrUtils
import Util
import Maybes
+import UniqFM
+import FastString
\end{code}
| Just ty2' <- coreView ty2 = match menv subst ty1 ty2'
match menv subst (TyVarTy tv1) ty2
+ | Just ty1' <- lookupVarEnv subst tv1' -- tv1' is already bound
+ = if tcEqTypeX (nukeRnEnvL rn_env) ty1' ty2
+ -- ty1 has no locally-bound variables, hence nukeRnEnvL
+ -- Note tcEqType...we are doing source-type matching here
+ then Just subst
+ else Nothing -- ty2 doesn't match
+
| tv1' `elemVarSet` me_tmpls menv
- = case lookupVarEnv subst tv1' of
- Nothing -- No existing binding
- | any (inRnEnvR rn_env) (varSetElems (tyVarsOfType ty2))
- -> Nothing -- Occurs check
- | otherwise
- -> do { subst1 <- match_kind menv subst tv1 ty2
- ; return (extendVarEnv subst1 tv1' ty2) }
+ = if any (inRnEnvR rn_env) (varSetElems (tyVarsOfType ty2))
+ then Nothing -- Occurs check
+ else do { subst1 <- match_kind menv subst tv1 ty2
-- Note [Matching kinds]
-
- Just ty1' -- There is an existing binding; check whether ty2 matches it
- | 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
- | otherwise -> Nothing -- ty2 doesn't match
-
+ ; return (extendVarEnv subst1 tv1' ty2) }
| otherwise -- tv1 is not a template tyvar
= case ty2 of
TyVarTy tv2 | tv1' == rnOccR rn_env tv2 -> Just subst
- other -> Nothing
+ _ -> Nothing
where
rn_env = me_env menv
tv1' = rnOccL rn_env tv1
= do { subst' <- match menv subst ty1a ty2a
; match menv subst' ty1b ty2b }
-match menv subst ty1 ty2
+match _ _ _ _
= Nothing
--------------
-- Match the kind of the template tyvar with the kind of Type
-- Note [Matching kinds]
match_kind menv subst tv ty
- | isCoVar tv = do { let (ty1,ty2) = splitCoercionKind (tyVarKind tv)
+ | isCoVar tv = do { let (ty1,ty2) = coVarKind tv
(ty3,ty4) = coercionKind ty
; subst1 <- match menv subst ty1 ty3
; match menv subst1 ty2 ty4 }
-- thing to do. C.f. Note [Matching variable types] in Rules.lhs
--------------
+match_tys :: MatchEnv -> TvSubstEnv -> [Type] -> [Type] -> Maybe TvSubstEnv
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 _ 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_list _ _ _ _ = Nothing
--------------
+match_pred :: MatchEnv -> TvSubstEnv -> PredType -> PredType -> Maybe TvSubstEnv
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
+match_pred _ _ _ _ = Nothing
\end{code}
| Just (f1, a1) <- repSplitAppTy_maybe ty1
= cant_match f1 f2 || cant_match a1 a2
- cant_match ty1 ty2 = False -- Safe!
+ cant_match _ _ = False -- Safe!
-- Things we could add;
-- foralls
-- look through newtypes
-- take account of tyvar bindings (EQ example above)
-\end{code}
\ No newline at end of file
+\end{code}
+
+
+%************************************************************************
+%* *
+ What a refinement is
+%* *
+%************************************************************************
+
+\begin{code}
+data Refinement = Reft InScopeSet InternalReft
+
+type InternalReft = TyVarEnv (Coercion, Type)
+-- INVARIANT: a->(co,ty) then co :: (a~ty)
+-- Not necessarily idemopotent
+
+instance Outputable Refinement where
+ ppr (Reft _in_scope env)
+ = ptext (sLit "Refinement") <+>
+ braces (ppr env)
+
+emptyRefinement :: Refinement
+emptyRefinement = (Reft emptyInScopeSet emptyVarEnv)
+
+isEmptyRefinement :: Refinement -> Bool
+isEmptyRefinement (Reft _ env) = isEmptyVarEnv env
+
+refineType :: Refinement -> Type -> Maybe (Coercion, Type)
+-- Apply the refinement to the type.
+-- If (refineType r ty) = (co, ty')
+-- Then co :: ty~ty'
+-- Nothing => the refinement does nothing to this type
+refineType (Reft in_scope env) ty
+ | not (isEmptyVarEnv env), -- Common case
+ any (`elemVarEnv` env) (varSetElems (tyVarsOfType ty))
+ = Just (substTy co_subst ty, substTy tv_subst ty)
+ | otherwise
+ = Nothing -- The type doesn't mention any refined type variables
+ where
+ tv_subst = mkTvSubst in_scope (mapVarEnv snd env)
+ co_subst = mkTvSubst in_scope (mapVarEnv fst env)
+
+refinePred :: Refinement -> PredType -> Maybe (Coercion, PredType)
+refinePred (Reft in_scope env) pred
+ | not (isEmptyVarEnv env), -- Common case
+ any (`elemVarEnv` env) (varSetElems (tyVarsOfPred pred))
+ = Just (mkPredTy (substPred co_subst pred), substPred tv_subst pred)
+ | otherwise
+ = Nothing -- The type doesn't mention any refined type variables
+ where
+ tv_subst = mkTvSubst in_scope (mapVarEnv snd env)
+ co_subst = mkTvSubst in_scope (mapVarEnv fst env)
+
+refineResType :: Refinement -> Type -> Maybe (Coercion, Type)
+-- Like refineType, but returns the 'sym' coercion
+-- If (refineResType r ty) = (co, ty')
+-- Then co :: ty'~ty
+refineResType reft ty
+ = case refineType reft ty of
+ Just (co, ty1) -> Just (mkSymCoercion co, ty1)
+ Nothing -> Nothing
+\end{code}
+
+
+%************************************************************************
+%* *
+ Simple generation of a type refinement
+%* *
+%************************************************************************
+
+\begin{code}
+matchRefine :: [TyVar] -> [Coercion] -> Refinement
+\end{code}
+
+Given a list of coercions, where for each coercion c::(ty1~ty2), the type ty2
+is a specialisation of ty1, produce a type refinement that maps the variables
+of ty1 to the corresponding sub-terms of ty2 using appropriate coercions; eg,
+
+ matchRefine (co :: [(a, b)] ~ [(c, Maybe d)])
+ = { right (left (right co)) :: a ~ c
+ , right (right co) :: b ~ Maybe d
+ }
+
+Precondition: The rhs types must indeed be a specialisation of the lhs types;
+ i.e., some free variables of the lhs are replaced with either distinct free
+ variables or proper type terms to obtain the rhs. (We don't perform full
+ unification or type matching here!)
+
+NB: matchRefine does *not* expand the type synonyms.
+
+\begin{code}
+matchRefine in_scope_tvs cos
+ = Reft in_scope (foldr plusVarEnv emptyVarEnv (map refineOne cos))
+ where
+ in_scope = mkInScopeSet (mkVarSet in_scope_tvs)
+ -- NB: in_scope_tvs include both coercion variables
+ -- *and* the tyvars in their kinds
+
+ refineOne co = refine co ty1 ty2
+ where
+ (ty1, ty2) = coercionKind co
+
+ refine co (TyVarTy tv) ty = unitVarEnv tv (co, ty)
+ refine co (TyConApp _ tys) (TyConApp _ tys') = refineArgs co tys tys'
+ refine _ (PredTy _) (PredTy _) =
+ error "Unify.matchRefine: PredTy"
+ refine co (FunTy arg res) (FunTy arg' res') =
+ refine (mkRightCoercion (mkLeftCoercion co)) arg arg'
+ `plusVarEnv`
+ refine (mkRightCoercion co) res res'
+ refine co (AppTy fun arg) (AppTy fun' arg') =
+ refine (mkLeftCoercion co) fun fun'
+ `plusVarEnv`
+ refine (mkRightCoercion co) arg arg'
+ refine co (ForAllTy tv ty) (ForAllTy _tv ty') =
+ refine (mkForAllCoercion tv co) ty ty' `delVarEnv` tv
+ refine _ _ _ = error "RcGadt.matchRefine: mismatch"
+
+ refineArgs :: Coercion -> [Type] -> [Type] -> InternalReft
+ refineArgs co tys tys' =
+ fst $ foldr refineArg (emptyVarEnv, id) (zip tys tys')
+ where
+ refineArg (ty, ty') (reft, coWrapper)
+ = (refine (mkRightCoercion (coWrapper co)) ty ty' `plusVarEnv` reft,
+ mkLeftCoercion . coWrapper)
+\end{code}
+
+
+%************************************************************************
+%* *
+ 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 <- unifyList emptyTvSubstEnv tys1 tys2
+
+ -- Find the fixed point of the resulting non-idempotent substitution
+ ; let in_scope = mkInScopeSet (tvs1 `unionVarSet` tvs2)
+ tv_env = fixTvSubstEnv in_scope subst
+
+ ; return (mkTvSubst in_scope tv_env) }
+ where
+ tvs1 = tyVarsOfTypes tys1
+ tvs2 = tyVarsOfTypes tys2
+
+----------------------------
+-- XXX Can we do this more nicely, by exploiting laziness?
+-- Or avoid needing it in the first place?
+fixTvSubstEnv :: InScopeSet -> TvSubstEnv -> TvSubstEnv
+fixTvSubstEnv in_scope env = f env
+ where
+ f e = let e' = mapUFM (substTy (mkTvSubst in_scope e)) e
+ in if and $ eltsUFM $ intersectUFM_C tcEqType e e'
+ then e
+ else f e'
+
+\end{code}
+
+
+%************************************************************************
+%* *
+ The workhorse
+%* *
+%************************************************************************
+
+\begin{code}
+unify :: TvSubstEnv -- An existing substitution to extend
+ -> Type -> Type -- Types to be unified, and witness of their equality
+ -> 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.
+
+-- Respects newtypes, PredTypes
+
+-- in unify, any NewTcApps/Preds should be taken at face value
+unify subst (TyVarTy tv1) ty2 = uVar subst tv1 ty2
+unify subst ty1 (TyVarTy tv2) = uVar subst tv2 ty1
+
+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 subst (PredTy p1) (PredTy p2) = unify_pred subst p1 p2
+
+unify subst (TyConApp tyc1 tys1) (TyConApp tyc2 tys2)
+ | tyc1 == tyc2 = unify_tys subst tys1 tys2
+
+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 subst (AppTy ty1a ty1b) ty2
+ | Just (ty2a, ty2b) <- repSplitAppTy_maybe ty2
+ = do { subst' <- unify subst ty1a ty2a
+ ; unify 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 _ ty1 ty2 = failWith (misMatch ty1 ty2)
+ -- ForAlls??
+
+------------------------------
+unify_pred :: TvSubstEnv -> PredType -> PredType -> UM TvSubstEnv
+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 _ p1 p2 = failWith (misMatch (PredTy p1) (PredTy p2))
+
+------------------------------
+unify_tys :: TvSubstEnv -> [Type] -> [Type] -> UM TvSubstEnv
+unify_tys subst xs ys = unifyList subst xs ys
+
+unifyList :: TvSubstEnv -> [Type] -> [Type] -> UM TvSubstEnv
+unifyList subst orig_xs orig_ys
+ = go subst orig_xs orig_ys
+ where
+ go subst [] [] = return subst
+ go subst (x:xs) (y:ys) = do { subst' <- unify subst x y
+ ; go subst' xs ys }
+ go _ _ _ = failWith (lengthMisMatch orig_xs orig_ys)
+
+---------------------------------
+uVar :: TvSubstEnv -- An existing substitution to extend
+ -> TyVar -- Type variable to be unified
+ -> Type -- with this type
+ -> UM TvSubstEnv
+
+-- PRE-CONDITION: in the call (uVar swap r tv1 ty), we know that
+-- if swap=False (tv1~ty)
+-- if swap=True (ty~tv1)
+
+uVar subst tv1 ty
+ = -- Check to see whether tv1 is refined by the substitution
+ case (lookupVarEnv subst tv1) of
+ Just ty' -> unify subst ty' ty -- Yes, call back into unify'
+ Nothing -> uUnrefined subst -- No, continue
+ tv1 ty ty
+
+uUnrefined :: TvSubstEnv -- An existing substitution to extend
+ -> TyVar -- Type variable to be unified
+ -> Type -- with this type
+ -> Type -- (version w/ expanded synonyms)
+ -> UM TvSubstEnv
+
+-- We know that tv1 isn't refined
+
+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' ty'
+
+ -- So both are unrefined; next, see if the kinds force the direction
+ | eqKind k1 k2 -- Can update either; so check the bind-flags
+ = do { b1 <- tvBindFlag tv1
+ ; b2 <- tvBindFlag tv2
+ ; case (b1,b2) of
+ (BindMe, _) -> bind tv1 ty2
+ (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' -- 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
+ = bindTv subst tv1 ty2 -- Bind tyvar to the synonym if poss
+ where
+ 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 :: TvSubstEnv -> TyVar -> Type -> UM TvSubstEnv
+bindTv subst tv ty -- ty is not a type variable
+ = do { b <- tvBindFlag tv
+ ; case b of
+ Skolem -> failWith (misMatch (TyVarTy tv) ty)
+ BindMe -> return $ extendVarEnv subst tv ty
+ }
+\end{code}
+
+%************************************************************************
+%* *
+ Binding decisions
+%* *
+%************************************************************************
+
+\begin{code}
+data BindFlag
+ = BindMe -- A regular type variable
+
+ | Skolem -- This type variable is a skolem constant
+ -- Don't bind it; it only matches itself
+\end{code}
+
+
+%************************************************************************
+%* *
+ Unification monad
+%* *
+%************************************************************************
+
+\begin{code}
+newtype UM a = UM { unUM :: (TyVar -> BindFlag)
+ -> MaybeErr Message a }
+
+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 Message a
+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 fail succ -> Maybe succ
+maybeErrToMaybe (Succeeded a) = Just a
+maybeErrToMaybe (Failed _) = 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 :: Type -> Type -> SDoc
+misMatch t1 t2
+ = ptext (sLit "Can't match types") <+> quotes (ppr t1) <+>
+ ptext (sLit "and") <+> quotes (ppr t2)
+
+lengthMisMatch :: [Type] -> [Type] -> SDoc
+lengthMisMatch tys1 tys2
+ = sep [ptext (sLit "Can't match unequal length lists"),
+ nest 2 (ppr tys1), nest 2 (ppr tys2) ]
+
+kindMisMatch :: TyVar -> Type -> SDoc
+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 :: TyVar -> Type -> SDoc
+occursCheck tv ty
+ = hang (ptext (sLit "Can't construct the infinite type"))
+ 2 (ppr tv <+> equals <+> ppr ty)
+\end{code}
projects / ghc-hetmet.git / blobdiff