X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=ghc%2Fcompiler%2Ftypecheck%2FTcMType.lhs;h=9947d826e4e9f592b1a7b8bcbc9f5fff03557523;hb=8a86866e9e382c1d4d06cad722ddbe965d09997c;hp=15d415003a0ddd3c0d619d018c7995866a0a8466;hpb=e78b0e0e18134acb175af2e656ce22988284af33;p=ghc-hetmet.git diff --git a/ghc/compiler/typecheck/TcMType.lhs b/ghc/compiler/typecheck/TcMType.lhs index 15d4150..9947d82 100644 --- a/ghc/compiler/typecheck/TcMType.lhs +++ b/ghc/compiler/typecheck/TcMType.lhs @@ -12,10 +12,11 @@ module TcMType ( -------------------------------- -- Creating new mutable type variables newTyVar, - newTyVarTy, -- Kind -> NF_TcM TcType - newTyVarTys, -- Int -> Kind -> NF_TcM [TcType] - newKindVar, newKindVars, newBoxityVar, + newTyVarTy, -- Kind -> TcM TcType + newTyVarTys, -- Int -> Kind -> TcM [TcType] + newKindVar, newKindVars, newOpenTypeKind, putTcTyVar, getTcTyVar, + newMutTyVar, readMutTyVar, writeMutTyVar, newHoleTyVarTy, readHoleResult, zapToType, @@ -29,12 +30,14 @@ module TcMType ( SourceTyCtxt(..), checkValidTheta, checkValidTyCon, checkValidClass, checkValidInstHead, instTypeErr, checkAmbiguity, + arityErr, -------------------------------- -- Zonking + zonkType, zonkTcTyVar, zonkTcTyVars, zonkTcTyVarsAndFV, zonkTcType, zonkTcTypes, zonkTcClassConstraints, zonkTcThetaType, - zonkTcPredType, zonkTcTypeToType, zonkTcTyVarToTyVar, zonkKindEnv, + zonkTcPredType, zonkTcTyVarToTyVar, zonkKindEnv, ) where @@ -43,15 +46,15 @@ module TcMType ( -- friends: import TypeRep ( Type(..), SourceType(..), TyNote(..), -- Friend; can see representation - Kind, ThetaType + Kind, ThetaType, typeCon ) import TcType ( TcType, TcThetaType, TcTauType, TcPredType, TcTyVarSet, TcKind, TcTyVar, TyVarDetails(..), - tcEqType, tcCmpPred, + tcEqType, tcCmpPred, isClassPred, tcSplitPhiTy, tcSplitPredTy_maybe, tcSplitAppTy_maybe, tcSplitTyConApp_maybe, tcSplitForAllTys, - tcIsTyVarTy, tcSplitSigmaTy, - isUnLiftedType, isIPPred, isHoleTyVar, + tcIsTyVarTy, tcSplitSigmaTy, mkTyConApp, + isUnLiftedType, isIPPred, isHoleTyVar, isTyVarTy, mkAppTy, mkTyVarTy, mkTyVarTys, tyVarsOfPred, getClassPredTys_maybe, @@ -59,38 +62,30 @@ import TcType ( TcType, TcThetaType, TcTauType, TcPredType, liftedTypeKind, openTypeKind, defaultKind, superKind, superBoxity, liftedBoxity, typeKind, tyVarsOfType, tyVarsOfTypes, - eqKind, isTypeKind, isAnyTypeKind, - + eqKind, isTypeKind, isFFIArgumentTy, isFFIImportResultTy ) -import qualified Type ( splitFunTys ) import Subst ( Subst, mkTopTyVarSubst, substTy ) import Class ( Class, DefMeth(..), classArity, className, classBigSig ) -import TyCon ( TyCon, mkPrimTyCon, isSynTyCon, isUnboxedTupleTyCon, - tyConArity, tyConName, tyConKind, tyConTheta, +import TyCon ( TyCon, isSynTyCon, isUnboxedTupleTyCon, + tyConArity, tyConName, tyConTheta, getSynTyConDefn, tyConDataCons ) import DataCon ( DataCon, dataConWrapId, dataConName, dataConSig, dataConFieldLabels ) import FieldLabel ( fieldLabelName, fieldLabelType ) -import PrimRep ( PrimRep(VoidRep) ) -import Var ( TyVar, idType, idName, tyVarKind, tyVarName, isTyVar, mkTyVar, isMutTyVar ) +import Var ( TyVar, idType, idName, tyVarKind, tyVarName, isTyVar, + mkTyVar, mkMutTyVar, isMutTyVar, mutTyVarRef ) -- others: import Generics ( validGenericMethodType ) -import TcMonad -- TcType, amongst others -import TysWiredIn ( voidTy, listTyCon, tupleTyCon ) +import TcRnMonad -- TcType, amongst others import PrelNames ( cCallableClassKey, cReturnableClassKey, hasKey ) import ForeignCall ( Safety(..) ) import FunDeps ( grow ) import PprType ( pprPred, pprSourceType, pprTheta, pprClassPred ) -import Name ( Name, NamedThing(..), setNameUnique, mkSystemName, - mkInternalName, mkDerivedTyConOcc - ) +import Name ( Name, setNameUnique, mkSystemTvNameEncoded ) import VarSet -import BasicTypes ( Boxity(Boxed) ) import CmdLineOpts ( dopt, DynFlag(..) ) -import Unique ( Uniquable(..) ) -import SrcLoc ( noSrcLoc ) -import Util ( nOfThem, isSingleton, equalLength ) +import Util ( nOfThem, isSingleton, equalLength, notNull ) import ListSetOps ( equivClasses, removeDups ) import Outputable \end{code} @@ -103,33 +98,44 @@ import Outputable %************************************************************************ \begin{code} -newTyVar :: Kind -> NF_TcM TcTyVar +newMutTyVar :: Name -> Kind -> TyVarDetails -> TcM TyVar +newMutTyVar name kind details + = do { ref <- newMutVar Nothing ; + return (mkMutTyVar name kind details ref) } + +readMutTyVar :: TyVar -> TcM (Maybe Type) +readMutTyVar tyvar = readMutVar (mutTyVarRef tyvar) + +writeMutTyVar :: TyVar -> Maybe Type -> TcM () +writeMutTyVar tyvar val = writeMutVar (mutTyVarRef tyvar) val + +newTyVar :: Kind -> TcM TcTyVar newTyVar kind - = tcGetUnique `thenNF_Tc` \ uniq -> - tcNewMutTyVar (mkSystemName uniq FSLIT("t")) kind VanillaTv + = newUnique `thenM` \ uniq -> + newMutTyVar (mkSystemTvNameEncoded uniq FSLIT("t")) kind VanillaTv -newTyVarTy :: Kind -> NF_TcM TcType +newTyVarTy :: Kind -> TcM TcType newTyVarTy kind - = newTyVar kind `thenNF_Tc` \ tc_tyvar -> - returnNF_Tc (TyVarTy tc_tyvar) + = newTyVar kind `thenM` \ tc_tyvar -> + returnM (TyVarTy tc_tyvar) -newTyVarTys :: Int -> Kind -> NF_TcM [TcType] -newTyVarTys n kind = mapNF_Tc newTyVarTy (nOfThem n kind) +newTyVarTys :: Int -> Kind -> TcM [TcType] +newTyVarTys n kind = mappM newTyVarTy (nOfThem n kind) -newKindVar :: NF_TcM TcKind +newKindVar :: TcM TcKind newKindVar - = tcGetUnique `thenNF_Tc` \ uniq -> - tcNewMutTyVar (mkSystemName uniq FSLIT("k")) superKind VanillaTv `thenNF_Tc` \ kv -> - returnNF_Tc (TyVarTy kv) - -newKindVars :: Int -> NF_TcM [TcKind] -newKindVars n = mapNF_Tc (\ _ -> newKindVar) (nOfThem n ()) - -newBoxityVar :: NF_TcM TcKind -newBoxityVar - = tcGetUnique `thenNF_Tc` \ uniq -> - tcNewMutTyVar (mkSystemName uniq FSLIT("bx")) superBoxity VanillaTv `thenNF_Tc` \ kv -> - returnNF_Tc (TyVarTy kv) + = newUnique `thenM` \ uniq -> + newMutTyVar (mkSystemTvNameEncoded uniq FSLIT("k")) superKind VanillaTv `thenM` \ kv -> + returnM (TyVarTy kv) + +newKindVars :: Int -> TcM [TcKind] +newKindVars n = mappM (\ _ -> newKindVar) (nOfThem n ()) + +newOpenTypeKind :: TcM TcKind -- Returns the kind (Type bx), where bx is fresh +newOpenTypeKind + = newUnique `thenM` \ uniq -> + newMutTyVar (mkSystemTvNameEncoded uniq FSLIT("bx")) superBoxity VanillaTv `thenM` \ kv -> + returnM (mkTyConApp typeCon [TyVarTy kv]) \end{code} @@ -140,33 +146,33 @@ newBoxityVar %************************************************************************ \begin{code} -newHoleTyVarTy :: NF_TcM TcType - = tcGetUnique `thenNF_Tc` \ uniq -> - tcNewMutTyVar (mkSystemName uniq FSLIT("h")) openTypeKind HoleTv `thenNF_Tc` \ tv -> - returnNF_Tc (TyVarTy tv) +newHoleTyVarTy :: TcM TcType + = newUnique `thenM` \ uniq -> + newMutTyVar (mkSystemTvNameEncoded uniq FSLIT("h")) openTypeKind HoleTv `thenM` \ tv -> + returnM (TyVarTy tv) -readHoleResult :: TcType -> NF_TcM TcType +readHoleResult :: TcType -> TcM TcType -- Read the answer out of a hole, constructed by newHoleTyVarTy readHoleResult (TyVarTy tv) = ASSERT( isHoleTyVar tv ) - getTcTyVar tv `thenNF_Tc` \ maybe_res -> + getTcTyVar tv `thenM` \ maybe_res -> case maybe_res of - Just ty -> returnNF_Tc ty + Just ty -> returnM ty Nothing -> pprPanic "readHoleResult: empty" (ppr tv) readHoleResult ty = pprPanic "readHoleResult: not hole" (ppr ty) -zapToType :: TcType -> NF_TcM TcType +zapToType :: TcType -> TcM TcType zapToType (TyVarTy tv) | isHoleTyVar tv - = getTcTyVar tv `thenNF_Tc` \ maybe_res -> + = getTcTyVar tv `thenM` \ maybe_res -> case maybe_res of - Nothing -> newTyVarTy openTypeKind `thenNF_Tc` \ ty -> - putTcTyVar tv ty `thenNF_Tc_` - returnNF_Tc ty - Just ty -> returnNF_Tc ty -- No need to loop; we never + Nothing -> newTyVarTy openTypeKind `thenM` \ ty -> + putTcTyVar tv ty `thenM_` + returnM ty + Just ty -> returnM ty -- No need to loop; we never -- have chains of holes -zapToType other_ty = returnNF_Tc other_ty +zapToType other_ty = returnM other_ty \end{code} %************************************************************************ @@ -179,20 +185,20 @@ Instantiating a bunch of type variables \begin{code} tcInstTyVars :: TyVarDetails -> [TyVar] - -> NF_TcM ([TcTyVar], [TcType], Subst) + -> TcM ([TcTyVar], [TcType], Subst) tcInstTyVars tv_details tyvars - = mapNF_Tc (tcInstTyVar tv_details) tyvars `thenNF_Tc` \ tc_tyvars -> + = mappM (tcInstTyVar tv_details) tyvars `thenM` \ tc_tyvars -> let tys = mkTyVarTys tc_tyvars in - returnNF_Tc (tc_tyvars, tys, mkTopTyVarSubst tyvars tys) + returnM (tc_tyvars, tys, mkTopTyVarSubst tyvars tys) -- Since the tyvars are freshly made, -- they cannot possibly be captured by -- any existing for-alls. Hence mkTopTyVarSubst tcInstTyVar tv_details tyvar - = tcGetUnique `thenNF_Tc` \ uniq -> + = newUnique `thenM` \ uniq -> let name = setNameUnique (tyVarName tyvar) uniq -- Note that we don't change the print-name @@ -202,9 +208,9 @@ tcInstTyVar tv_details tyvar -- Better watch out for this. If worst comes to worst, just -- use mkSystemName. in - tcNewMutTyVar name (tyVarKind tyvar) tv_details + newMutTyVar name (tyVarKind tyvar) tv_details -tcInstType :: TyVarDetails -> TcType -> NF_TcM ([TcTyVar], TcThetaType, TcType) +tcInstType :: TyVarDetails -> TcType -> TcM ([TcTyVar], TcThetaType, TcType) -- tcInstType instantiates the outer-level for-alls of a TcType with -- fresh (mutable) type variables, splits off the dictionary part, -- and returns the pieces. @@ -215,13 +221,13 @@ tcInstType tv_details ty let (theta, tau) = tcSplitPhiTy rho in - returnNF_Tc ([], theta, tau) + returnM ([], theta, tau) - (tyvars, rho) -> tcInstTyVars tv_details tyvars `thenNF_Tc` \ (tyvars', _, tenv) -> + (tyvars, rho) -> tcInstTyVars tv_details tyvars `thenM` \ (tyvars', _, tenv) -> let (theta, tau) = tcSplitPhiTy (substTy tenv rho) in - returnNF_Tc (tyvars', theta, tau) + returnM (tyvars', theta, tau) \end{code} @@ -232,8 +238,8 @@ tcInstType tv_details ty %************************************************************************ \begin{code} -putTcTyVar :: TcTyVar -> TcType -> NF_TcM TcType -getTcTyVar :: TcTyVar -> NF_TcM (Maybe TcType) +putTcTyVar :: TcTyVar -> TcType -> TcM TcType +getTcTyVar :: TcTyVar -> TcM (Maybe TcType) \end{code} Putting is easy: @@ -242,18 +248,18 @@ Putting is easy: putTcTyVar tyvar ty | not (isMutTyVar tyvar) = pprTrace "putTcTyVar" (ppr tyvar) $ - returnNF_Tc ty + returnM ty | otherwise = ASSERT( isMutTyVar tyvar ) - tcWriteMutTyVar tyvar (Just ty) `thenNF_Tc_` - returnNF_Tc ty + writeMutTyVar tyvar (Just ty) `thenM_` + returnM ty \end{code} Getting is more interesting. The easy thing to do is just to read, thus: \begin{verbatim} -getTcTyVar tyvar = tcReadMutTyVar tyvar +getTcTyVar tyvar = readMutTyVar tyvar \end{verbatim} But it's more fun to short out indirections on the way: If this @@ -266,33 +272,33 @@ We return Nothing iff the original box was unbound. getTcTyVar tyvar | not (isMutTyVar tyvar) = pprTrace "getTcTyVar" (ppr tyvar) $ - returnNF_Tc (Just (mkTyVarTy tyvar)) + returnM (Just (mkTyVarTy tyvar)) | otherwise = ASSERT2( isMutTyVar tyvar, ppr tyvar ) - tcReadMutTyVar tyvar `thenNF_Tc` \ maybe_ty -> + readMutTyVar tyvar `thenM` \ maybe_ty -> case maybe_ty of - Just ty -> short_out ty `thenNF_Tc` \ ty' -> - tcWriteMutTyVar tyvar (Just ty') `thenNF_Tc_` - returnNF_Tc (Just ty') + Just ty -> short_out ty `thenM` \ ty' -> + writeMutTyVar tyvar (Just ty') `thenM_` + returnM (Just ty') - Nothing -> returnNF_Tc Nothing + Nothing -> returnM Nothing -short_out :: TcType -> NF_TcM TcType +short_out :: TcType -> TcM TcType short_out ty@(TyVarTy tyvar) | not (isMutTyVar tyvar) - = returnNF_Tc ty + = returnM ty | otherwise - = tcReadMutTyVar tyvar `thenNF_Tc` \ maybe_ty -> + = readMutTyVar tyvar `thenM` \ maybe_ty -> case maybe_ty of - Just ty' -> short_out ty' `thenNF_Tc` \ ty' -> - tcWriteMutTyVar tyvar (Just ty') `thenNF_Tc_` - returnNF_Tc ty' + Just ty' -> short_out ty' `thenM` \ ty' -> + writeMutTyVar tyvar (Just ty') `thenM_` + returnM ty' - other -> returnNF_Tc ty + other -> returnM ty -short_out other_ty = returnNF_Tc other_ty +short_out other_ty = returnM other_ty \end{code} @@ -305,53 +311,53 @@ short_out other_ty = returnNF_Tc other_ty ----------------- Type variables \begin{code} -zonkTcTyVars :: [TcTyVar] -> NF_TcM [TcType] -zonkTcTyVars tyvars = mapNF_Tc zonkTcTyVar tyvars +zonkTcTyVars :: [TcTyVar] -> TcM [TcType] +zonkTcTyVars tyvars = mappM zonkTcTyVar tyvars -zonkTcTyVarsAndFV :: [TcTyVar] -> NF_TcM TcTyVarSet -zonkTcTyVarsAndFV tyvars = mapNF_Tc zonkTcTyVar tyvars `thenNF_Tc` \ tys -> - returnNF_Tc (tyVarsOfTypes tys) +zonkTcTyVarsAndFV :: [TcTyVar] -> TcM TcTyVarSet +zonkTcTyVarsAndFV tyvars = mappM zonkTcTyVar tyvars `thenM` \ tys -> + returnM (tyVarsOfTypes tys) -zonkTcTyVar :: TcTyVar -> NF_TcM TcType -zonkTcTyVar tyvar = zonkTyVar (\ tv -> returnNF_Tc (TyVarTy tv)) tyvar +zonkTcTyVar :: TcTyVar -> TcM TcType +zonkTcTyVar tyvar = zonkTyVar (\ tv -> returnM (TyVarTy tv)) tyvar \end{code} ----------------- Types \begin{code} -zonkTcType :: TcType -> NF_TcM TcType -zonkTcType ty = zonkType (\ tv -> returnNF_Tc (TyVarTy tv)) ty +zonkTcType :: TcType -> TcM TcType +zonkTcType ty = zonkType (\ tv -> returnM (TyVarTy tv)) ty -zonkTcTypes :: [TcType] -> NF_TcM [TcType] -zonkTcTypes tys = mapNF_Tc zonkTcType tys +zonkTcTypes :: [TcType] -> TcM [TcType] +zonkTcTypes tys = mappM zonkTcType tys -zonkTcClassConstraints cts = mapNF_Tc zonk cts +zonkTcClassConstraints cts = mappM zonk cts where zonk (clas, tys) - = zonkTcTypes tys `thenNF_Tc` \ new_tys -> - returnNF_Tc (clas, new_tys) + = zonkTcTypes tys `thenM` \ new_tys -> + returnM (clas, new_tys) -zonkTcThetaType :: TcThetaType -> NF_TcM TcThetaType -zonkTcThetaType theta = mapNF_Tc zonkTcPredType theta +zonkTcThetaType :: TcThetaType -> TcM TcThetaType +zonkTcThetaType theta = mappM zonkTcPredType theta -zonkTcPredType :: TcPredType -> NF_TcM TcPredType +zonkTcPredType :: TcPredType -> TcM TcPredType zonkTcPredType (ClassP c ts) - = zonkTcTypes ts `thenNF_Tc` \ new_ts -> - returnNF_Tc (ClassP c new_ts) + = zonkTcTypes ts `thenM` \ new_ts -> + returnM (ClassP c new_ts) zonkTcPredType (IParam n t) - = zonkTcType t `thenNF_Tc` \ new_t -> - returnNF_Tc (IParam n new_t) + = zonkTcType t `thenM` \ new_t -> + returnM (IParam n new_t) \end{code} ------------------- These ...ToType, ...ToKind versions are used at the end of type checking \begin{code} -zonkKindEnv :: [(Name, TcKind)] -> NF_TcM [(Name, Kind)] +zonkKindEnv :: [(Name, TcKind)] -> TcM [(Name, Kind)] zonkKindEnv pairs - = mapNF_Tc zonk_it pairs + = mappM zonk_it pairs where - zonk_it (name, tc_kind) = zonkType zonk_unbound_kind_var tc_kind `thenNF_Tc` \ kind -> - returnNF_Tc (name, kind) + zonk_it (name, tc_kind) = zonkType zonk_unbound_kind_var tc_kind `thenM` \ kind -> + returnM (name, kind) -- When zonking a kind, we want to -- zonk a *kind* variable to (Type *) @@ -360,68 +366,6 @@ zonkKindEnv pairs | tyVarKind kv `eqKind` superBoxity = putTcTyVar kv liftedBoxity | otherwise = pprPanic "zonkKindEnv" (ppr kv) -zonkTcTypeToType :: TcType -> NF_TcM Type -zonkTcTypeToType ty = zonkType zonk_unbound_tyvar ty - where - -- Zonk a mutable but unbound type variable to an arbitrary type - -- We know it's unbound even though we don't carry an environment, - -- because at the binding site for a type variable we bind the - -- mutable tyvar to a fresh immutable one. So the mutable store - -- plays the role of an environment. If we come across a mutable - -- type variable that isn't so bound, it must be completely free. - zonk_unbound_tyvar tv = putTcTyVar tv (mkArbitraryType tv) - - --- When the type checker finds a type variable with no binding, --- which means it can be instantiated with an arbitrary type, it --- usually instantiates it to Void. Eg. --- --- length [] --- ===> --- length Void (Nil Void) --- --- But in really obscure programs, the type variable might have --- a kind other than *, so we need to invent a suitably-kinded type. --- --- This commit uses --- Void for kind * --- List for kind *->* --- Tuple for kind *->...*->* --- --- which deals with most cases. (Previously, it only dealt with --- kind *.) --- --- In the other cases, it just makes up a TyCon with a suitable --- kind. If this gets into an interface file, anyone reading that --- file won't understand it. This is fixable (by making the client --- of the interface file make up a TyCon too) but it is tiresome and --- never happens, so I am leaving it - -mkArbitraryType :: TcTyVar -> Type --- Make up an arbitrary type whose kind is the same as the tyvar. --- We'll use this to instantiate the (unbound) tyvar. -mkArbitraryType tv - | isAnyTypeKind kind = voidTy -- The vastly common case - | otherwise = TyConApp tycon [] - where - kind = tyVarKind tv - (args,res) = Type.splitFunTys kind -- Kinds are simple; use Type.splitFunTys - - tycon | kind `eqKind` tyConKind listTyCon -- *->* - = listTyCon -- No tuples this size - - | all isTypeKind args && isTypeKind res - = tupleTyCon Boxed (length args) -- *-> ... ->*->* - - | otherwise - = pprTrace "Urk! Inventing strangely-kinded void TyCon" (ppr tc_name) $ - mkPrimTyCon tc_name kind 0 [] VoidRep - -- Same name as the tyvar, apart from making it start with a colon (sigh) - -- I dread to think what will happen if this gets out into an - -- interface file. Catastrophe likely. Major sigh. - - tc_name = mkInternalName (getUnique tv) (mkDerivedTyConOcc (getOccName tv)) noSrcLoc - -- zonkTcTyVarToTyVar is applied to the *binding* occurrence -- of a type variable, at the *end* of type checking. It changes -- the *mutable* type variable into an *immutable* one. @@ -430,7 +374,7 @@ mkArbitraryType tv -- Now any bound occurences of the original type variable will get -- zonked to the immutable version. -zonkTcTyVarToTyVar :: TcTyVar -> NF_TcM TyVar +zonkTcTyVarToTyVar :: TcTyVar -> TcM TyVar zonkTcTyVarToTyVar tv = let -- Make an immutable version, defaulting @@ -443,13 +387,47 @@ zonkTcTyVarToTyVar tv in -- If the type variable is mutable, then bind it to immut_tv_ty -- so that all other occurrences of the tyvar will get zapped too - zonkTyVar zap tv `thenNF_Tc` \ ty2 -> + zonkTyVar zap tv `thenM` \ ty2 -> + -- This warning shows up if the allegedly-unbound tyvar is + -- already bound to something. It can actually happen, and + -- in a harmless way (see [Silly Type Synonyms] below) so + -- it's only a warning WARN( not (immut_tv_ty `tcEqType` ty2), ppr tv $$ ppr immut_tv $$ ppr ty2 ) - returnNF_Tc immut_tv + returnM immut_tv \end{code} +[Silly Type Synonyms] + +Consider this: + type C u a = u -- Note 'a' unused + + foo :: (forall a. C u a -> C u a) -> u + foo x = ... + + bar :: Num u => u + bar = foo (\t -> t + t) + +* From the (\t -> t+t) we get type {Num d} => d -> d + where d is fresh. + +* Now unify with type of foo's arg, and we get: + {Num (C d a)} => C d a -> C d a + where a is fresh. + +* Now abstract over the 'a', but float out the Num (C d a) constraint + because it does not 'really' mention a. (see Type.tyVarsOfType) + The arg to foo becomes + /\a -> \t -> t+t + +* So we get a dict binding for Num (C d a), which is zonked to give + a = () + +* Then the /\a abstraction has a zonked 'a' in it. + +All very silly. I think its harmless to ignore the problem. + %************************************************************************ %* * @@ -466,32 +444,32 @@ zonkTcTyVarToTyVar tv -- For tyvars bound at a for-all, zonkType zonks them to an immutable -- type variable and zonks the kind too -zonkType :: (TcTyVar -> NF_TcM Type) -- What to do with unbound mutable type variables +zonkType :: (TcTyVar -> TcM Type) -- What to do with unbound mutable type variables -- see zonkTcType, and zonkTcTypeToType -> TcType - -> NF_TcM Type + -> TcM Type zonkType unbound_var_fn ty = go ty where - go (TyConApp tycon tys) = mapNF_Tc go tys `thenNF_Tc` \ tys' -> - returnNF_Tc (TyConApp tycon tys') + go (TyConApp tycon tys) = mappM go tys `thenM` \ tys' -> + returnM (TyConApp tycon tys') - go (NoteTy (SynNote ty1) ty2) = go ty1 `thenNF_Tc` \ ty1' -> - go ty2 `thenNF_Tc` \ ty2' -> - returnNF_Tc (NoteTy (SynNote ty1') ty2') + go (NoteTy (SynNote ty1) ty2) = go ty1 `thenM` \ ty1' -> + go ty2 `thenM` \ ty2' -> + returnM (NoteTy (SynNote ty1') ty2') go (NoteTy (FTVNote _) ty2) = go ty2 -- Discard free-tyvar annotations - go (SourceTy p) = go_pred p `thenNF_Tc` \ p' -> - returnNF_Tc (SourceTy p') + go (SourceTy p) = go_pred p `thenM` \ p' -> + returnM (SourceTy p') - go (FunTy arg res) = go arg `thenNF_Tc` \ arg' -> - go res `thenNF_Tc` \ res' -> - returnNF_Tc (FunTy arg' res') + go (FunTy arg res) = go arg `thenM` \ arg' -> + go res `thenM` \ res' -> + returnM (FunTy arg' res') - go (AppTy fun arg) = go fun `thenNF_Tc` \ fun' -> - go arg `thenNF_Tc` \ arg' -> - returnNF_Tc (mkAppTy fun' arg') + go (AppTy fun arg) = go fun `thenM` \ fun' -> + go arg `thenM` \ arg' -> + returnM (mkAppTy fun' arg') -- NB the mkAppTy; we might have instantiated a -- type variable to a type constructor, so we need -- to pull the TyConApp to the top. @@ -499,28 +477,28 @@ zonkType unbound_var_fn ty -- The two interesting cases! go (TyVarTy tyvar) = zonkTyVar unbound_var_fn tyvar - go (ForAllTy tyvar ty) = zonkTcTyVarToTyVar tyvar `thenNF_Tc` \ tyvar' -> - go ty `thenNF_Tc` \ ty' -> - returnNF_Tc (ForAllTy tyvar' ty') + go (ForAllTy tyvar ty) = zonkTcTyVarToTyVar tyvar `thenM` \ tyvar' -> + go ty `thenM` \ ty' -> + returnM (ForAllTy tyvar' ty') - go_pred (ClassP c tys) = mapNF_Tc go tys `thenNF_Tc` \ tys' -> - returnNF_Tc (ClassP c tys') - go_pred (NType tc tys) = mapNF_Tc go tys `thenNF_Tc` \ tys' -> - returnNF_Tc (NType tc tys') - go_pred (IParam n ty) = go ty `thenNF_Tc` \ ty' -> - returnNF_Tc (IParam n ty') + go_pred (ClassP c tys) = mappM go tys `thenM` \ tys' -> + returnM (ClassP c tys') + go_pred (NType tc tys) = mappM go tys `thenM` \ tys' -> + returnM (NType tc tys') + go_pred (IParam n ty) = go ty `thenM` \ ty' -> + returnM (IParam n ty') -zonkTyVar :: (TcTyVar -> NF_TcM Type) -- What to do for an unbound mutable variable - -> TcTyVar -> NF_TcM TcType +zonkTyVar :: (TcTyVar -> TcM Type) -- What to do for an unbound mutable variable + -> TcTyVar -> TcM TcType zonkTyVar unbound_var_fn tyvar | not (isMutTyVar tyvar) -- Not a mutable tyvar. This can happen when -- zonking a forall type, when the bound type variable -- needn't be mutable = ASSERT( isTyVar tyvar ) -- Should not be any immutable kind vars - returnNF_Tc (TyVarTy tyvar) + returnM (TyVarTy tyvar) | otherwise - = getTcTyVar tyvar `thenNF_Tc` \ maybe_ty -> + = getTcTyVar tyvar `thenM` \ maybe_ty -> case maybe_ty of Nothing -> unbound_var_fn tyvar -- Mutable and unbound Just other_ty -> zonkType unbound_var_fn other_ty -- Bound @@ -603,7 +581,7 @@ pprUserTypeCtxt (RuleSigCtxt n) = ptext SLIT("the type signature on") <+> quotes checkValidType :: UserTypeCtxt -> Type -> TcM () -- Checks that the type is valid for the given context checkValidType ctxt ty - = doptsTc Opt_GlasgowExts `thenNF_Tc` \ gla_exts -> + = doptM Opt_GlasgowExts `thenM` \ gla_exts -> let rank | gla_exts = Arbitrary | otherwise @@ -637,10 +615,10 @@ checkValidType ctxt ty -- but for type synonyms we allow them even at -- top level in - tcAddErrCtxt (checkTypeCtxt ctxt ty) $ + addErrCtxt (checkTypeCtxt ctxt ty) $ -- Check that the thing has kind Type, and is lifted if necessary - checkTc kind_ok (kindErr actual_kind) `thenTc_` + checkTc kind_ok (kindErr actual_kind) `thenM_` -- Check the internal validity of the type itself check_poly_type rank ubx_tup ty @@ -658,7 +636,7 @@ checkTypeCtxt ctxt ty -- This shows up in the complaint about -- case C a where -- op :: Eq a => a -> a -ppr_ty ty | null forall_tvs && not (null theta) = pprTheta theta <+> ptext SLIT("=>") <+> ppr tau +ppr_ty ty | null forall_tvs && notNull theta = pprTheta theta <+> ptext SLIT("=>") <+> ppr tau | otherwise = ppr ty where (forall_tvs, theta, tau) = tcSplitSigmaTy ty @@ -685,9 +663,9 @@ check_poly_type rank ubx_tup ty = let (tvs, theta, tau) = tcSplitSigmaTy ty in - check_valid_theta SigmaCtxt theta `thenTc_` - check_tau_type (decRank rank) ubx_tup tau `thenTc_` - checkFreeness tvs theta `thenTc_` + check_valid_theta SigmaCtxt theta `thenM_` + check_tau_type (decRank rank) ubx_tup tau `thenM_` + checkFreeness tvs theta `thenM_` checkAmbiguity tvs theta (tyVarsOfType tau) ---------------------------------------- @@ -711,7 +689,7 @@ check_arg_type :: Type -> TcM () -- Anyway, they are dealt with by a special case in check_tau_type check_arg_type ty - = check_tau_type (Rank 0) UT_NotOk ty `thenTc_` + = check_tau_type (Rank 0) UT_NotOk ty `thenM_` checkTc (not (isUnLiftedType ty)) (unliftedArgErr ty) ---------------------------------------- @@ -720,41 +698,59 @@ check_tau_type :: Rank -> UbxTupFlag -> Type -> TcM () -- No foralls otherwise check_tau_type rank ubx_tup ty@(ForAllTy _ _) = failWithTc (forAllTyErr ty) -check_tau_type rank ubx_tup (SourceTy sty) = getDOptsTc `thenNF_Tc` \ dflags -> +check_tau_type rank ubx_tup (SourceTy sty) = getDOpts `thenM` \ dflags -> check_source_ty dflags TypeCtxt sty -check_tau_type rank ubx_tup (TyVarTy _) = returnTc () +check_tau_type rank ubx_tup (TyVarTy _) = returnM () check_tau_type rank ubx_tup ty@(FunTy arg_ty res_ty) - = check_poly_type rank UT_NotOk arg_ty `thenTc_` + = check_poly_type rank UT_NotOk arg_ty `thenM_` check_tau_type rank UT_Ok res_ty check_tau_type rank ubx_tup (AppTy ty1 ty2) - = check_arg_type ty1 `thenTc_` check_arg_type ty2 + = check_arg_type ty1 `thenM_` check_arg_type ty2 -check_tau_type rank ubx_tup (NoteTy note ty) - = check_tau_type rank ubx_tup ty +check_tau_type rank ubx_tup (NoteTy (SynNote syn) ty) -- Synonym notes are built only when the synonym is -- saturated (see Type.mkSynTy) - -- Not checking the 'note' part allows us to instantiate a synonym - -- defn with a for-all type, or with a partially-applied type synonym, - -- but that seems OK too + = doptM Opt_GlasgowExts `thenM` \ gla_exts -> + (if gla_exts then + -- If -fglasgow-exts then don't check the 'note' part. + -- This allows us to instantiate a synonym defn with a + -- for-all type, or with a partially-applied type synonym. + -- e.g. type T a b = a + -- type S m = m () + -- f :: S (T Int) + -- Here, T is partially applied, so it's illegal in H98. + -- But if you expand S first, then T we get just + -- f :: Int + -- which is fine. + returnM () + else + -- For H98, do check the un-expanded part + check_tau_type rank ubx_tup syn + ) `thenM_` + + check_tau_type rank ubx_tup ty + +check_tau_type rank ubx_tup (NoteTy other_note ty) + = check_tau_type rank ubx_tup ty check_tau_type rank ubx_tup ty@(TyConApp tc tys) | isSynTyCon tc = -- NB: Type.mkSynTy builds a TyConApp (not a NoteTy) for an unsaturated - -- synonym application, leaving it to checkValidType (i.e. right here + -- synonym application, leaving it to checkValidType (i.e. right here) -- to find the error - checkTc syn_arity_ok arity_msg `thenTc_` - mapTc_ check_arg_type tys + checkTc syn_arity_ok arity_msg `thenM_` + mappM_ check_arg_type tys | isUnboxedTupleTyCon tc - = doptsTc Opt_GlasgowExts `thenNF_Tc` \ gla_exts -> - checkTc (ubx_tup_ok gla_exts) ubx_tup_msg `thenTc_` - mapTc_ (check_tau_type (Rank 0) UT_Ok) tys + = doptM Opt_GlasgowExts `thenM` \ gla_exts -> + checkTc (ubx_tup_ok gla_exts) ubx_tup_msg `thenM_` + mappM_ (check_tau_type (Rank 0) UT_Ok) tys -- Args are allowed to be unlifted, or -- more unboxed tuples, so can't use check_arg_ty | otherwise - = mapTc_ check_arg_type tys + = mappM_ check_arg_type tys where ubx_tup_ok gla_exts = case ubx_tup of { UT_Ok -> gla_exts; other -> False } @@ -777,76 +773,6 @@ ubxArgTyErr ty = ptext SLIT("Illegal unboxed tuple type as function argument kindErr kind = ptext SLIT("Expecting an ordinary type, but found a type of kind") <+> ppr kind \end{code} -Check for ambiguity -~~~~~~~~~~~~~~~~~~~ - forall V. P => tau -is ambiguous if P contains generic variables -(i.e. one of the Vs) that are not mentioned in tau - -However, we need to take account of functional dependencies -when we speak of 'mentioned in tau'. Example: - class C a b | a -> b where ... -Then the type - forall x y. (C x y) => x -is not ambiguous because x is mentioned and x determines y - -NB; the ambiguity check is only used for *user* types, not for types -coming from inteface files. The latter can legitimately have -ambiguous types. Example - - class S a where s :: a -> (Int,Int) - instance S Char where s _ = (1,1) - f:: S a => [a] -> Int -> (Int,Int) - f (_::[a]) x = (a*x,b) - where (a,b) = s (undefined::a) - -Here the worker for f gets the type - fw :: forall a. S a => Int -> (# Int, Int #) - -If the list of tv_names is empty, we have a monotype, and then we -don't need to check for ambiguity either, because the test can't fail -(see is_ambig). - -\begin{code} -checkAmbiguity :: [TyVar] -> ThetaType -> TyVarSet -> TcM () -checkAmbiguity forall_tyvars theta tau_tyvars - = mapTc_ complain (filter is_ambig theta) - where - complain pred = addErrTc (ambigErr pred) - extended_tau_vars = grow theta tau_tyvars - is_ambig pred = any ambig_var (varSetElems (tyVarsOfPred pred)) - - ambig_var ct_var = (ct_var `elem` forall_tyvars) && - not (ct_var `elemVarSet` extended_tau_vars) - - is_free ct_var = not (ct_var `elem` forall_tyvars) - -ambigErr pred - = sep [ptext SLIT("Ambiguous constraint") <+> quotes (pprPred pred), - nest 4 (ptext SLIT("At least one of the forall'd type variables mentioned by the constraint") $$ - ptext SLIT("must be reachable from the type after the '=>'"))] -\end{code} - -In addition, GHC insists that at least one type variable -in each constraint is in V. So we disallow a type like - forall a. Eq b => b -> b -even in a scope where b is in scope. - -\begin{code} -checkFreeness forall_tyvars theta - = mapTc_ complain (filter is_free theta) - where - is_free pred = not (isIPPred pred) - && not (any bound_var (varSetElems (tyVarsOfPred pred))) - bound_var ct_var = ct_var `elem` forall_tyvars - complain pred = addErrTc (freeErr pred) - -freeErr pred - = sep [ptext SLIT("All of the type variables in the constraint") <+> quotes (pprPred pred) <+> - ptext SLIT("are already in scope"), - nest 4 (ptext SLIT("(at least one must be universally quantified here)")) - ] -\end{code} %************************************************************************ @@ -875,24 +801,28 @@ pprSourceTyCtxt TypeCtxt = ptext SLIT("the context of a type") \begin{code} checkValidTheta :: SourceTyCtxt -> ThetaType -> TcM () checkValidTheta ctxt theta - = tcAddErrCtxt (checkThetaCtxt ctxt theta) (check_valid_theta ctxt theta) + = addErrCtxt (checkThetaCtxt ctxt theta) (check_valid_theta ctxt theta) ------------------------- check_valid_theta ctxt [] - = returnTc () + = returnM () check_valid_theta ctxt theta - = getDOptsTc `thenNF_Tc` \ dflags -> - warnTc (not (null dups)) (dupPredWarn dups) `thenNF_Tc_` - mapTc_ (check_source_ty dflags ctxt) theta + = getDOpts `thenM` \ dflags -> + warnTc (notNull dups) (dupPredWarn dups) `thenM_` + -- Actually, in instance decls and type signatures, + -- duplicate constraints are eliminated by TcMonoType.hoistForAllTys, + -- so this error can only fire for the context of a class or + -- data type decl. + mappM_ (check_source_ty dflags ctxt) theta where (_,dups) = removeDups tcCmpPred theta ------------------------- check_source_ty dflags ctxt pred@(ClassP cls tys) = -- Class predicates are valid in all contexts - mapTc_ check_arg_type tys `thenTc_` - checkTc (arity == n_tys) arity_err `thenTc_` - checkTc (all tyvar_head tys || arby_preds_ok) + mappM_ check_arg_type tys `thenM_` + checkTc (arity == n_tys) arity_err `thenM_` + checkTc (check_class_pred_tys dflags ctxt tys) (predTyVarErr pred $$ how_to_allow) where @@ -901,12 +831,6 @@ check_source_ty dflags ctxt pred@(ClassP cls tys) n_tys = length tys arity_err = arityErr "Class" class_name arity n_tys - arby_preds_ok = case ctxt of - InstHeadCtxt -> True -- We check for instance-head formation - -- in checkValidInstHead - InstThetaCtxt -> dopt Opt_AllowUndecidableInstances dflags - other -> dopt Opt_GlasgowExts dflags - how_to_allow = case ctxt of InstHeadCtxt -> empty -- Should not happen InstThetaCtxt -> parens undecidableMsg @@ -922,12 +846,23 @@ check_source_ty dflags SigmaCtxt (IParam _ ty) = check_arg_type ty -- constraint Foo [Int] might come out of e,and applying the -- instance decl would show up two uses of ?x. -check_source_ty dflags TypeCtxt (NType tc tys) = mapTc_ check_arg_type tys +check_source_ty dflags TypeCtxt (NType tc tys) = mappM_ check_arg_type tys -- Catch-all check_source_ty dflags ctxt sty = failWithTc (badSourceTyErr sty) ------------------------- +check_class_pred_tys dflags ctxt tys + = case ctxt of + InstHeadCtxt -> True -- We check for instance-head + -- formation in checkValidInstHead + InstThetaCtxt -> undecidable_ok || all isTyVarTy tys + other -> gla_exts || all tyvar_head tys + where + undecidable_ok = dopt Opt_AllowUndecidableInstances dflags + gla_exts = dopt Opt_GlasgowExts dflags + +------------------------- tyvar_head ty -- Haskell 98 allows predicates of form | tcIsTyVarTy ty = True -- C (a ty1 .. tyn) | otherwise -- where a is a type variable @@ -936,14 +871,98 @@ tyvar_head ty -- Haskell 98 allows predicates of form Nothing -> False \end{code} +Check for ambiguity +~~~~~~~~~~~~~~~~~~~ + forall V. P => tau +is ambiguous if P contains generic variables +(i.e. one of the Vs) that are not mentioned in tau + +However, we need to take account of functional dependencies +when we speak of 'mentioned in tau'. Example: + class C a b | a -> b where ... +Then the type + forall x y. (C x y) => x +is not ambiguous because x is mentioned and x determines y + +NB; the ambiguity check is only used for *user* types, not for types +coming from inteface files. The latter can legitimately have +ambiguous types. Example + + class S a where s :: a -> (Int,Int) + instance S Char where s _ = (1,1) + f:: S a => [a] -> Int -> (Int,Int) + f (_::[a]) x = (a*x,b) + where (a,b) = s (undefined::a) + +Here the worker for f gets the type + fw :: forall a. S a => Int -> (# Int, Int #) + +If the list of tv_names is empty, we have a monotype, and then we +don't need to check for ambiguity either, because the test can't fail +(see is_ambig). + \begin{code} -badSourceTyErr sty = ptext SLIT("Illegal constraint") <+> pprSourceType sty -predTyVarErr pred = ptext SLIT("Non-type variables in constraint:") <+> pprPred pred -dupPredWarn dups = ptext SLIT("Duplicate constraint(s):") <+> pprWithCommas pprPred (map head dups) +checkAmbiguity :: [TyVar] -> ThetaType -> TyVarSet -> TcM () +checkAmbiguity forall_tyvars theta tau_tyvars + = mappM_ complain (filter is_ambig theta) + where + complain pred = addErrTc (ambigErr pred) + extended_tau_vars = grow theta tau_tyvars + + -- Only a *class* predicate can give rise to ambiguity + -- An *implicit parameter* cannot. For example: + -- foo :: (?x :: [a]) => Int + -- foo = length ?x + -- is fine. The call site will suppply a particular 'x' + is_ambig pred = isClassPred pred && + any ambig_var (varSetElems (tyVarsOfPred pred)) + + ambig_var ct_var = (ct_var `elem` forall_tyvars) && + not (ct_var `elemVarSet` extended_tau_vars) + +ambigErr pred + = sep [ptext SLIT("Ambiguous constraint") <+> quotes (pprPred pred), + nest 4 (ptext SLIT("At least one of the forall'd type variables mentioned by the constraint") $$ + ptext SLIT("must be reachable from the type after the '=>'"))] +\end{code} + +In addition, GHC insists that at least one type variable +in each constraint is in V. So we disallow a type like + forall a. Eq b => b -> b +even in a scope where b is in scope. +\begin{code} +checkFreeness forall_tyvars theta + = mappM_ complain (filter is_free theta) + where + is_free pred = not (isIPPred pred) + && not (any bound_var (varSetElems (tyVarsOfPred pred))) + bound_var ct_var = ct_var `elem` forall_tyvars + complain pred = addErrTc (freeErr pred) + +freeErr pred + = sep [ptext SLIT("All of the type variables in the constraint") <+> quotes (pprPred pred) <+> + ptext SLIT("are already in scope"), + nest 4 (ptext SLIT("(at least one must be universally quantified here)")) + ] +\end{code} + +\begin{code} checkThetaCtxt ctxt theta = vcat [ptext SLIT("In the context:") <+> pprTheta theta, ptext SLIT("While checking") <+> pprSourceTyCtxt ctxt ] + +badSourceTyErr sty = ptext SLIT("Illegal constraint") <+> pprSourceType sty +predTyVarErr pred = ptext SLIT("Non-type variables in constraint:") <+> pprPred pred +dupPredWarn dups = ptext SLIT("Duplicate constraint(s):") <+> pprWithCommas pprPred (map head dups) + +arityErr kind name n m + = hsep [ text kind, quotes (ppr name), ptext SLIT("should have"), + n_arguments <> comma, text "but has been given", int m] + where + n_arguments | n == 0 = ptext SLIT("no arguments") + | n == 1 = ptext SLIT("1 argument") + | True = hsep [int n, ptext SLIT("arguments")] \end{code} @@ -962,13 +981,13 @@ checkValidTyCon tc | isSynTyCon tc = checkValidType (TySynCtxt name) syn_rhs | otherwise = -- Check the context on the data decl - checkValidTheta (DataTyCtxt name) (tyConTheta tc) `thenTc_` + checkValidTheta (DataTyCtxt name) (tyConTheta tc) `thenM_` -- Check arg types of data constructors - mapTc_ checkValidDataCon data_cons `thenTc_` + mappM_ checkValidDataCon data_cons `thenM_` -- Check that fields with the same name share a type - mapTc_ check_fields groups + mappM_ check_fields groups where name = tyConName tc @@ -993,11 +1012,11 @@ checkValidTyCon tc checkValidDataCon :: DataCon -> TcM () checkValidDataCon con - = checkValidType ctxt (idType (dataConWrapId con)) `thenTc_` + = checkValidType ctxt (idType (dataConWrapId con)) `thenM_` -- This checks the argument types and -- ambiguity of the existential context (if any) - tcAddErrCtxt (existentialCtxt con) - (checkFreeness ex_tvs ex_theta) + addErrCtxt (existentialCtxt con) + (checkFreeness ex_tvs ex_theta) where ctxt = ConArgCtxt (dataConName con) (_, _, ex_tvs, ex_theta, _, _) = dataConSig con @@ -1018,17 +1037,17 @@ tied, so we can look at things freely. checkValidClass :: Class -> TcM () checkValidClass cls = -- CHECK ARITY 1 FOR HASKELL 1.4 - doptsTc Opt_GlasgowExts `thenTc` \ gla_exts -> + doptM Opt_GlasgowExts `thenM` \ gla_exts -> -- Check that the class is unary, unless GlaExs - checkTc (not (null tyvars)) (nullaryClassErr cls) `thenTc_` - checkTc (gla_exts || unary) (classArityErr cls) `thenTc_` + checkTc (notNull tyvars) (nullaryClassErr cls) `thenM_` + checkTc (gla_exts || unary) (classArityErr cls) `thenM_` -- Check the super-classes - checkValidTheta (ClassSCCtxt (className cls)) theta `thenTc_` + checkValidTheta (ClassSCCtxt (className cls)) theta `thenM_` -- Check the class operations - mapTc_ check_op op_stuff `thenTc_` + mappM_ check_op op_stuff `thenM_` -- Check that if the class has generic methods, then the -- class has only one parameter. We can't do generic @@ -1041,11 +1060,11 @@ checkValidClass cls no_generics = null [() | (_, GenDefMeth) <- op_stuff] check_op (sel_id, dm) - = checkValidTheta SigmaCtxt (tail theta) `thenTc_` + = checkValidTheta SigmaCtxt (tail theta) `thenM_` -- The 'tail' removes the initial (C a) from the -- class itself, leaving just the method type - checkValidType (FunSigCtxt op_name) tau `thenTc_` + checkValidType (FunSigCtxt op_name) tau `thenM_` -- Check that for a generic method, the type of -- the method is sufficiently simple @@ -1101,10 +1120,10 @@ checkValidInstHead ty -- Should be a source type Nothing -> failWithTc (instTypeErr (pprPred pred) empty) ; Just (clas,tys) -> - getDOptsTc `thenNF_Tc` \ dflags -> - mapTc_ check_arg_type tys `thenTc_` - check_inst_head dflags clas tys `thenTc_` - returnTc (clas, tys) + getDOpts `thenM` \ dflags -> + mappM_ check_arg_type tys `thenM_` + check_inst_head dflags clas tys `thenM_` + returnM (clas, tys) }} check_inst_head dflags clas tys @@ -1128,7 +1147,7 @@ check_inst_head dflags clas tys all tcIsTyVarTy arg_tys, -- Applied to type variables equalLength (varSetElems (tyVarsOfTypes arg_tys)) arg_tys -- This last condition checks that all the type variables are distinct - = returnTc () + = returnM () | otherwise = failWithTc (instTypeErr (pprClassPred clas tys) head_shape_msg) @@ -1145,8 +1164,8 @@ check_inst_head dflags clas tys check_tyvars dflags clas tys -- Check that at least one isn't a type variable -- unless -fallow-undecideable-instances - | dopt Opt_AllowUndecidableInstances dflags = returnTc () - | not (all tcIsTyVarTy tys) = returnTc () + | dopt Opt_AllowUndecidableInstances dflags = returnM () + | not (all tcIsTyVarTy tys) = returnM () | otherwise = failWithTc (instTypeErr (pprClassPred clas tys) msg) where msg = parens (ptext SLIT("There must be at least one non-type-variable in the instance head")