+++ /dev/null
-%
-% (c) The University of Glasgow 2006
-% (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
-%
-
-%************************************************************************
-%* *
- Type refinement for GADTs
-%* *
-%************************************************************************
-
-\begin{code}
-module TcGadt (
- Refinement, emptyRefinement, isEmptyRefinement,
- matchRefine,
- refineType, refinePred, refineResType,
- tcUnifyTys, BindFlag(..)
- ) where
-
-#include "HsVersions.h"
-
-import HsSyn
-import Coercion
-import Type
-
-import TypeRep
-import Var
-import VarEnv
-import VarSet
-import ErrUtils
-import Maybes
-import Control.Monad
-import Outputable
-import TcType
-import UniqFM
-import FastString
-\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 -> (HsWrapper, Type)
--- Like refineType, but returns the 'sym' coercion
--- If (refineResType r ty) = (co, ty')
--- Then co :: ty':=:ty
--- It's convenient to return a HsWrapper here
-refineResType reft ty
- = case refineType reft ty of
- Just (co, ty1) -> (WpCo (mkSymCoercion co), ty1)
- Nothing -> (idHsWrapper, ty)
-\end{code}
-
-
-%************************************************************************
-%* *
- Simple generation of a type refinement
-%* *
-%************************************************************************
-
-\begin{code}
-matchRefine :: [CoVar] -> 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 co_vars
- = Reft in_scope (foldr plusVarEnv emptyVarEnv (map refineOne co_vars))
- where
- in_scope = foldr extend emptyInScopeSet co_vars
-
- -- For each co_var, add it *and* the tyvars it mentions, to in_scope
- extend co_var in_scope
- = extendInScopeSetSet in_scope $
- extendVarSet (tyVarsOfType (tyVarKind co_var)) co_var
-
- refineOne co_var = refine (TyVarTy co_var) ty1 ty2
- where
- (ty1, ty2) = splitCoercionKind (tyVarKind co_var)
-
- refine co (TyVarTy tv) ty = unitVarEnv tv (co, ty)
- refine co (TyConApp _ tys) (TyConApp _ tys') = refineArgs co tys tys'
- refine co (NoteTy _ ty) ty' = refine co ty ty'
- refine co ty (NoteTy _ ty') = refine co ty ty'
- refine _ (PredTy _) (PredTy _) =
- error "TcGadt.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
---
--- We implement tcUnifyTys using the evidence-generating 'unify' function
--- in this module, even though we don't need to generate any evidence.
--- This is simply to avoid replicating all all the code for unify
-tcUnifyTys bind_fn tys1 tys2
- = maybeErrToMaybe $ initUM bind_fn $
- do { reft <- unifyList emptyInternalReft cos tys1 tys2
-
- -- Find the fixed point of the resulting non-idempotent substitution
- ; let in_scope = mkInScopeSet (tvs1 `unionVarSet` tvs2)
- tv_env = fixTvSubstEnv in_scope (mapVarEnv snd reft)
-
- ; return (mkTvSubst in_scope tv_env) }
- where
- tvs1 = tyVarsOfTypes tys1
- tvs2 = tyVarsOfTypes tys2
- cos = zipWith mkUnsafeCoercion tys1 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}
-emptyInternalReft :: InternalReft
-emptyInternalReft = emptyVarEnv
-
-unify :: InternalReft -- An existing substitution to extend
- -> Coercion -- Witness of their equality
- -> Type -> Type -- Types to be unified, and witness of their equality
- -> UM InternalReft -- 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.
-
--- PRE-CONDITION: in the call (unify r co ty1 ty2), we know that
--- co :: (ty1:=:ty2)
-
--- Respects newtypes, PredTypes
-
-unify subst co ty1 ty2 = -- pprTrace "unify" (ppr subst <+> pprParendType ty1 <+> pprParendType ty2) $
- unify_ subst co ty1 ty2
-
--- in unify_, any NewTcApps/Preds should be taken at face value
-unify_ subst co (TyVarTy tv1) ty2 = uVar False subst co tv1 ty2
-unify_ subst co ty1 (TyVarTy tv2) = uVar True subst co tv2 ty1
-
-unify_ subst co ty1 ty2 | Just ty1' <- tcView ty1 = unify subst co ty1' ty2
-unify_ subst co ty1 ty2 | Just ty2' <- tcView ty2 = unify subst co ty1 ty2'
-
-unify_ subst co (PredTy p1) (PredTy p2) = unify_pred subst co p1 p2
-
-unify_ subst co t1@(TyConApp tyc1 tys1) t2@(TyConApp tyc2 tys2)
- | tyc1 == tyc2 = unify_tys subst co tys1 tys2
-
-unify_ subst co (FunTy ty1a ty1b) (FunTy ty2a ty2b)
- = do { let [co1,co2] = decomposeCo 2 co
- ; subst' <- unify subst co1 ty1a ty2a
- ; unify subst' co2 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 co (AppTy ty1a ty1b) ty2
- | Just (ty2a, ty2b) <- repSplitAppTy_maybe ty2
- = do { subst' <- unify subst (mkLeftCoercion co) ty1a ty2a
- ; unify subst' (mkRightCoercion co) ty1b ty2b }
-
-unify_ subst co ty1 (AppTy ty2a ty2b)
- | Just (ty1a, ty1b) <- repSplitAppTy_maybe ty1
- = do { subst' <- unify subst (mkLeftCoercion co) ty1a ty2a
- ; unify subst' (mkRightCoercion co) ty1b ty2b }
-
-unify_ subst co ty1 ty2 = failWith (misMatch ty1 ty2)
- -- ForAlls??
-
-
-------------------------------
-unify_pred subst co (ClassP c1 tys1) (ClassP c2 tys2)
- | c1 == c2 = unify_tys subst co tys1 tys2
-unify_pred subst co (IParam n1 t1) (IParam n2 t2)
- | n1 == n2 = unify subst co t1 t2
-unify_pred subst co p1 p2 = failWith (misMatch (PredTy p1) (PredTy p2))
-
-------------------------------
-unify_tys :: InternalReft -> Coercion -> [Type] -> [Type] -> UM InternalReft
-unify_tys subst co xs ys
- = unifyList subst (decomposeCo (length xs) co) xs ys
-
-unifyList :: InternalReft -> [Coercion] -> [Type] -> [Type] -> UM InternalReft
-unifyList subst orig_cos orig_xs orig_ys
- = go subst orig_cos orig_xs orig_ys
- where
- go subst _ [] [] = return subst
- go subst (co:cos) (x:xs) (y:ys) = do { subst' <- unify subst co x y
- ; go subst' cos xs ys }
- go subst _ _ _ = failWith (lengthMisMatch orig_xs orig_ys)
-
----------------------------------
-uVar :: Bool -- Swapped
- -> InternalReft -- An existing substitution to extend
- -> Coercion
- -> TyVar -- Type variable to be unified
- -> Type -- with this type
- -> UM InternalReft
-
--- PRE-CONDITION: in the call (uVar swap r co tv1 ty), we know that
--- if swap=False co :: (tv1:=:ty)
--- if swap=True co :: (ty:=:tv1)
-
-uVar swap subst co tv1 ty
- = -- Check to see whether tv1 is refined by the substitution
- case (lookupVarEnv subst tv1) of
-
- -- Yes, call back into unify'
- Just (co',ty') -- co' :: (tv1:=:ty')
- | swap -- co :: (ty:=:tv1)
- -> unify subst (mkTransCoercion co co') ty ty'
- | otherwise -- co :: (tv1:=:ty)
- -> unify subst (mkTransCoercion (mkSymCoercion co') co) ty' ty
-
- -- No, continue
- Nothing -> uUnrefined swap subst co
- tv1 ty ty
-
-
-uUnrefined :: Bool -- Whether the input is swapped
- -> InternalReft -- An existing substitution to extend
- -> Coercion
- -> TyVar -- Type variable to be unified
- -> Type -- with this type
- -> Type -- (de-noted version)
- -> UM InternalReft
-
--- We know that tv1 isn't refined
--- PRE-CONDITION: in the call (uUnrefined False r co tv1 ty2 ty2'), we know that
--- co :: tv1:=:ty2
--- and if the first argument is True instead, we know
--- co :: ty2:=:tv1
-
-uUnrefined swap subst co tv1 ty2 ty2'
- | Just ty2'' <- tcView ty2'
- = uUnrefined swap subst co tv1 ty2 ty2'' -- Unwrap synonyms
- -- This is essential, in case we have
- -- type Foo a = a
- -- and then unify a :=: Foo a
-
-uUnrefined swap subst co tv1 ty2 (TyVarTy tv2)
- | tv1 == tv2 -- Same type variable
- = return subst
-
- -- Check to see whether tv2 is refined
- | Just (co',ty') <- lookupVarEnv subst tv2 -- co' :: tv2:=:ty'
- = uUnrefined False subst (mkTransCoercion (doSwap swap co) co') 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 swap tv1 ty2
-
- (AvoidMe, BindMe) -> bind (not swap) tv2 ty1
- (AvoidMe, _) -> bind swap tv1 ty2
-
- (WildCard, WildCard) -> return subst
- (WildCard, Skolem) -> return subst
- (WildCard, _) -> bind (not swap) tv2 ty1
-
- (Skolem, WildCard) -> return subst
- (Skolem, Skolem) -> failWith (misMatch ty1 ty2)
- (Skolem, _) -> bind (not swap) tv2 ty1
- }
-
- | k1 `isSubKind` k2 = bindTv (not swap) subst co tv2 ty1 -- Must update tv2
- | k2 `isSubKind` k1 = bindTv swap subst co tv1 ty2 -- Must update tv1
-
- | otherwise = failWith (kindMisMatch tv1 ty2)
- where
- ty1 = TyVarTy tv1
- k1 = tyVarKind tv1
- k2 = tyVarKind tv2
- bind swap tv ty = extendReft swap subst tv co ty
-
-uUnrefined swap subst co 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 swap subst co tv1 ty2 -- Bind tyvar to the synonym if poss
- where
- k1 = tyVarKind tv1
- k2 = typeKind ty2'
-
-substTvSet :: InternalReft -> 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 swap subst co 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 -> extendReft swap subst tv co ty
- }
-
-doSwap :: Bool -> Coercion -> Coercion
-doSwap swap co = if swap then mkSymCoercion co else co
-
-extendReft :: Bool
- -> InternalReft
- -> TyVar
- -> Coercion
- -> Type
- -> UM InternalReft
-extendReft swap subst tv co ty
- = ASSERT2( (coercionKindPredTy co1 `tcEqType` mkCoKind (mkTyVarTy tv) ty),
- (text "Refinement invariant failure: co = " <+> ppr co1 <+> ppr (coercionKindPredTy co1) $$ text "subst = " <+> ppr tv <+> ppr (mkCoKind (mkTyVarTy tv) ty)) )
- return (extendVarEnv subst tv (co1, ty))
- where
- co1 = doSwap swap co
-
-\end{code}
-
-%************************************************************************
-%* *
- Unification monad
-%* *
-%************************************************************************
-
-\begin{code}
-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 }
-
-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 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}
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