X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=ghc%2Fcompiler%2Ftypecheck%2FTcMType.lhs;h=174f9654b6b0cee9d93f752fcdd6d8471cb991ab;hb=fc13ed2ff4953be09d7d4fbe24ebab059254b724;hp=07166d8b720a31426ee594d811a9524e43e4a74d;hpb=91c750cbd18e3d610b0db498ded38d5b3c5adfac;p=ghc-hetmet.git diff --git a/ghc/compiler/typecheck/TcMType.lhs b/ghc/compiler/typecheck/TcMType.lhs index 07166d8..174f965 100644 --- a/ghc/compiler/typecheck/TcMType.lhs +++ b/ghc/compiler/typecheck/TcMType.lhs @@ -11,29 +11,31 @@ module TcMType ( -------------------------------- -- Creating new mutable type variables - newTyVar, newHoleTyVarTy, - newTyVarTy, -- Kind -> NF_TcM TcType - newTyVarTys, -- Int -> Kind -> NF_TcM [TcType] - newKindVar, newKindVars, newBoxityVar, + newTyVar, newSigTyVar, + newTyVarTy, -- Kind -> TcM TcType + newTyVarTys, -- Int -> Kind -> TcM [TcType] + newKindVar, newKindVars, newOpenTypeKind, putTcTyVar, getTcTyVar, + newMutTyVar, readMutTyVar, writeMutTyVar, -------------------------------- -- Instantiation - tcInstTyVar, tcInstTyVars, - tcInstSigTyVars, tcInstType, tcInstSigType, - tcSplitRhoTyM, + tcInstTyVar, tcInstTyVars, tcInstType, -------------------------------- -- Checking type validity - Rank, UserTypeCtxt(..), checkValidType, pprUserTypeCtxt, - SourceTyCtxt(..), checkValidTheta, - checkValidInstHead, instTypeErr, + Rank, UserTypeCtxt(..), checkValidType, pprHsSigCtxt, + SourceTyCtxt(..), checkValidTheta, checkFreeness, + checkValidInstHead, instTypeErr, checkAmbiguity, + arityErr, -------------------------------- -- Zonking - zonkTcTyVar, zonkTcTyVars, zonkTcTyVarsAndFV, zonkTcSigTyVars, + zonkType, + zonkTcTyVar, zonkTcTyVars, zonkTcTyVarsAndFV, zonkTcType, zonkTcTypes, zonkTcClassConstraints, zonkTcThetaType, - zonkTcPredType, zonkTcTypeToType, zonkTcTyVarToTyVar, zonkKindEnv, + zonkTcPredType, zonkTcTyVarToTyVar, + zonkTcKindToKind ) where @@ -41,50 +43,42 @@ module TcMType ( -- friends: -import TypeRep ( Type(..), SourceType(..), TyNote(..), -- Friend; can see representation +import HsSyn ( LHsType ) +import TypeRep ( Type(..), PredType(..), TyNote(..), -- Friend; can see representation Kind, ThetaType ) import TcType ( TcType, TcThetaType, TcTauType, TcPredType, TcTyVarSet, TcKind, TcTyVar, TyVarDetails(..), - tcEqType, tcCmpPred, - tcSplitRhoTy, tcSplitPredTy_maybe, tcSplitAppTy_maybe, + tcEqType, tcCmpPred, isClassPred, mkTyConApp, typeCon, + tcSplitPhiTy, tcSplitPredTy_maybe, tcSplitAppTy_maybe, tcSplitTyConApp_maybe, tcSplitForAllTys, - tcGetTyVar, tcIsTyVarTy, tcSplitSigmaTy, + tcIsTyVarTy, tcSplitSigmaTy, tcIsTyVarTy, isUnLiftedType, isIPPred, mkAppTy, mkTyVarTy, mkTyVarTys, tyVarsOfPred, getClassPredTys_maybe, - liftedTypeKind, openTypeKind, defaultKind, superKind, + liftedTypeKind, defaultKind, superKind, superBoxity, liftedBoxity, typeKind, tyVarsOfType, tyVarsOfTypes, - eqKind, isTypeKind, - - isFFIArgumentTy, isFFIImportResultTy - ) + eqKind, isTypeKind, + pprPred, pprTheta, pprClassPred ) import Subst ( Subst, mkTopTyVarSubst, substTy ) import Class ( Class, classArity, className ) -import TyCon ( TyCon, mkPrimTyCon, isSynTyCon, isUnboxedTupleTyCon, +import TyCon ( TyCon, isSynTyCon, isUnboxedTupleTyCon, tyConArity, tyConName ) -import PrimRep ( PrimRep(VoidRep) ) -import Var ( TyVar, tyVarKind, tyVarName, isTyVar, mkTyVar, isMutTyVar ) +import Var ( TyVar, tyVarKind, tyVarName, isTyVar, + mkTyVar, mkMutTyVar, isMutTyVar, mutTyVarRef ) -- others: -import TcMonad -- TcType, amongst others -import TysWiredIn ( voidTy ) -import PrelNames ( cCallableClassKey, cReturnableClassKey, hasKey ) -import ForeignCall ( Safety(..) ) +import TcRnMonad -- TcType, amongst others import FunDeps ( grow ) -import PprType ( pprPred, pprSourceType, pprTheta, pprClassPred ) -import Name ( Name, NamedThing(..), setNameUnique, mkSysLocalName, - mkLocalName, mkDerivedTyConOcc - ) +import Name ( Name, setNameUnique, mkSystemTvNameEncoded ) import VarSet import CmdLineOpts ( dopt, DynFlag(..) ) -import Unique ( Uniquable(..) ) -import SrcLoc ( noSrcLoc ) -import Util ( nOfThem, isSingleton, equalLength ) +import Util ( nOfThem, isSingleton, equalLength, notNull ) import ListSetOps ( removeDups ) +import SrcLoc ( unLoc ) import Outputable \end{code} @@ -96,69 +90,53 @@ import Outputable %************************************************************************ \begin{code} -newTyVar :: Kind -> NF_TcM TcTyVar -newTyVar kind - = tcGetUnique `thenNF_Tc` \ uniq -> - tcNewMutTyVar (mkSysLocalName uniq SLIT("t")) kind VanillaTv - -newTyVarTy :: Kind -> NF_TcM TcType -newTyVarTy kind - = newTyVar kind `thenNF_Tc` \ tc_tyvar -> - returnNF_Tc (TyVarTy tc_tyvar) +newMutTyVar :: Name -> Kind -> TyVarDetails -> TcM TyVar +newMutTyVar name kind details + = do { ref <- newMutVar Nothing ; + return (mkMutTyVar name kind details ref) } -newHoleTyVarTy :: NF_TcM TcType - = tcGetUnique `thenNF_Tc` \ uniq -> - tcNewMutTyVar (mkSysLocalName uniq SLIT("h")) openTypeKind HoleTv `thenNF_Tc` \ tv -> - returnNF_Tc (TyVarTy tv) +readMutTyVar :: TyVar -> TcM (Maybe Type) +readMutTyVar tyvar = readMutVar (mutTyVarRef tyvar) -newTyVarTys :: Int -> Kind -> NF_TcM [TcType] -newTyVarTys n kind = mapNF_Tc newTyVarTy (nOfThem n kind) +writeMutTyVar :: TyVar -> Maybe Type -> TcM () +writeMutTyVar tyvar val = writeMutVar (mutTyVarRef tyvar) val -newKindVar :: NF_TcM TcKind -newKindVar - = tcGetUnique `thenNF_Tc` \ uniq -> - tcNewMutTyVar (mkSysLocalName uniq SLIT("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 (mkSysLocalName uniq SLIT("bx")) superBoxity VanillaTv `thenNF_Tc` \ kv -> - returnNF_Tc (TyVarTy kv) -\end{code} +newTyVar :: Kind -> TcM TcTyVar +newTyVar kind + = newUnique `thenM` \ uniq -> + newMutTyVar (mkSystemTvNameEncoded uniq FSLIT("t")) kind VanillaTv +newSigTyVar :: Kind -> TcM TcTyVar +newSigTyVar kind + = newUnique `thenM` \ uniq -> + newMutTyVar (mkSystemTvNameEncoded uniq FSLIT("s")) kind SigTv -%************************************************************************ -%* * -\subsection{Type instantiation} -%* * -%************************************************************************ +newTyVarTy :: Kind -> TcM TcType +newTyVarTy kind + = newTyVar kind `thenM` \ tc_tyvar -> + returnM (TyVarTy tc_tyvar) -I don't understand why this is needed -An old comments says "No need for tcSplitForAllTyM because a type - variable can't be instantiated to a for-all type" -But the same is true of rho types! +newTyVarTys :: Int -> Kind -> TcM [TcType] +newTyVarTys n kind = mappM newTyVarTy (nOfThem n kind) -\begin{code} -tcSplitRhoTyM :: TcType -> NF_TcM (TcThetaType, TcType) -tcSplitRhoTyM t - = go t t [] - where - -- A type variable is never instantiated to a dictionary type, - -- so we don't need to do a tcReadVar on the "arg". - go syn_t (FunTy arg res) ts = case tcSplitPredTy_maybe arg of - Just pair -> go res res (pair:ts) - Nothing -> returnNF_Tc (reverse ts, syn_t) - go syn_t (NoteTy n t) ts = go syn_t t ts - go syn_t (TyVarTy tv) ts = getTcTyVar tv `thenNF_Tc` \ maybe_ty -> - case maybe_ty of - Just ty | not (tcIsTyVarTy ty) -> go syn_t ty ts - other -> returnNF_Tc (reverse ts, syn_t) - go syn_t (UsageTy _ t) ts = go syn_t t ts - go syn_t t ts = returnNF_Tc (reverse ts, syn_t) +newKindVar :: TcM TcKind +newKindVar + = 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 ()) + +newBoxityVar :: TcM TcKind -- Really TcBoxity + = newUnique `thenM` \ uniq -> + newMutTyVar (mkSystemTvNameEncoded uniq FSLIT("bx")) + superBoxity VanillaTv `thenM` \ kv -> + returnM (TyVarTy kv) + +newOpenTypeKind :: TcM TcKind +newOpenTypeKind = newBoxityVar `thenM` \ bx_var -> + returnM (mkTyConApp typeCon [bx_var]) \end{code} @@ -171,21 +149,21 @@ tcSplitRhoTyM t Instantiating a bunch of type variables \begin{code} -tcInstTyVars :: [TyVar] - -> NF_TcM ([TcTyVar], [TcType], Subst) +tcInstTyVars :: TyVarDetails -> [TyVar] + -> TcM ([TcTyVar], [TcType], Subst) -tcInstTyVars tyvars - = mapNF_Tc tcInstTyVar tyvars `thenNF_Tc` \ tc_tyvars -> +tcInstTyVars tv_details 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 tyvar - = tcGetUnique `thenNF_Tc` \ uniq -> +tcInstTyVar tv_details tyvar + = newUnique `thenM` \ uniq -> let name = setNameUnique (tyVarName tyvar) uniq -- Note that we don't change the print-name @@ -193,66 +171,31 @@ tcInstTyVar tyvar -- that two different tyvars will print the same way -- in an error message. -dppr-debug will show up the difference -- Better watch out for this. If worst comes to worst, just - -- use mkSysLocalName. + -- use mkSystemName. in - tcNewMutTyVar name (tyVarKind tyvar) VanillaTv - -tcInstSigTyVars :: TyVarDetails -> [TyVar] -> NF_TcM [TcTyVar] -tcInstSigTyVars details tyvars -- Very similar to tcInstTyVar - = tcGetUniques `thenNF_Tc` \ uniqs -> - listTc [ ASSERT( not (kind `eqKind` openTypeKind) ) -- Shouldn't happen - tcNewMutTyVar name kind details - | (tyvar, uniq) <- tyvars `zip` uniqs, - let name = setNameUnique (tyVarName tyvar) uniq, - let kind = tyVarKind tyvar - ] -\end{code} - -@tcInstType@ instantiates the outer-level for-alls of a TcType with -fresh type variables, splits off the dictionary part, and returns the results. + newMutTyVar name (tyVarKind tyvar) tv_details -\begin{code} -tcInstType :: TcType -> NF_TcM ([TcTyVar], TcThetaType, TcType) -tcInstType ty +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. +tcInstType tv_details ty = case tcSplitForAllTys ty of - ([], rho) -> -- There may be overloading but no type variables; + ([], rho) -> -- There may be overloading despite no type variables; -- (?x :: Int) => Int -> Int let - (theta, tau) = tcSplitRhoTy rho -- Used to be tcSplitRhoTyM + (theta, tau) = tcSplitPhiTy rho in - returnNF_Tc ([], theta, tau) + returnM ([], theta, tau) - (tyvars, rho) -> tcInstTyVars tyvars `thenNF_Tc` \ (tyvars', _, tenv) -> + (tyvars, rho) -> tcInstTyVars tv_details tyvars `thenM` \ (tyvars', _, tenv) -> let - (theta, tau) = tcSplitRhoTy (substTy tenv rho) -- Used to be tcSplitRhoTyM + (theta, tau) = tcSplitPhiTy (substTy tenv rho) in - returnNF_Tc (tyvars', theta, tau) - - -tcInstSigType :: TyVarDetails -> Type -> NF_TcM ([TcTyVar], TcThetaType, TcType) --- Very similar to tcInstSigType, but uses signature type variables --- Also, somewhat arbitrarily, don't deal with the monomorphic case so efficiently -tcInstSigType tv_details poly_ty - = let - (tyvars, rho) = tcSplitForAllTys poly_ty - in - tcInstSigTyVars tv_details tyvars `thenNF_Tc` \ tyvars' -> - -- Make *signature* type variables - - let - tyvar_tys' = mkTyVarTys tyvars' - rho' = substTy (mkTopTyVarSubst tyvars tyvar_tys') rho - -- mkTopTyVarSubst because the tyvars' are fresh - - (theta', tau') = tcSplitRhoTy rho' - -- This splitRhoTy tries hard to make sure that tau' is a type synonym - -- wherever possible, which can improve interface files. - in - returnNF_Tc (tyvars', theta', tau') + returnM (tyvars', theta, tau) \end{code} - %************************************************************************ %* * \subsection{Putting and getting mutable type variables} @@ -260,8 +203,8 @@ tcInstSigType tv_details poly_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: @@ -270,19 +213,18 @@ Putting is easy: putTcTyVar tyvar ty | not (isMutTyVar tyvar) = pprTrace "putTcTyVar" (ppr tyvar) $ - returnNF_Tc ty + returnM ty | otherwise = ASSERT( isMutTyVar tyvar ) - UASSERT2( not (isUTy ty), ppr tyvar <+> ppr ty ) - 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 @@ -295,33 +237,33 @@ 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} @@ -334,99 +276,59 @@ short_out other_ty = returnNF_Tc other_ty ----------------- Type variables \begin{code} -zonkTcTyVars :: [TcTyVar] -> NF_TcM [TcType] -zonkTcTyVars tyvars = mapNF_Tc zonkTcTyVar tyvars - -zonkTcTyVarsAndFV :: [TcTyVar] -> NF_TcM TcTyVarSet -zonkTcTyVarsAndFV tyvars = mapNF_Tc zonkTcTyVar tyvars `thenNF_Tc` \ tys -> - returnNF_Tc (tyVarsOfTypes tys) - -zonkTcTyVar :: TcTyVar -> NF_TcM TcType -zonkTcTyVar tyvar = zonkTyVar (\ tv -> returnNF_Tc (TyVarTy tv)) tyvar - -zonkTcSigTyVars :: [TcTyVar] -> NF_TcM [TcTyVar] --- This guy is to zonk the tyvars we're about to feed into tcSimplify --- Usually this job is done by checkSigTyVars, but in a couple of places --- that is overkill, so we use this simpler chap -zonkTcSigTyVars tyvars - = zonkTcTyVars tyvars `thenNF_Tc` \ tys -> - returnNF_Tc (map (tcGetTyVar "zonkTcSigTyVars") tys) +zonkTcTyVars :: [TcTyVar] -> TcM [TcType] +zonkTcTyVars tyvars = mappM zonkTcTyVar tyvars + +zonkTcTyVarsAndFV :: [TcTyVar] -> TcM TcTyVarSet +zonkTcTyVarsAndFV tyvars = mappM zonkTcTyVar tyvars `thenM` \ tys -> + returnM (tyVarsOfTypes tys) + +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 pairs - = mapNF_Tc zonk_it pairs - where - zonk_it (name, tc_kind) = zonkType zonk_unbound_kind_var tc_kind `thenNF_Tc` \ kind -> - returnNF_Tc (name, kind) - +zonkTcKindToKind :: TcKind -> TcM Kind +zonkTcKindToKind tc_kind + = zonkType zonk_unbound_kind_var tc_kind + where -- When zonking a kind, we want to -- zonk a *kind* variable to (Type *) -- zonk a *boxity* variable to * - zonk_unbound_kind_var kv | tyVarKind kv `eqKind` superKind = putTcTyVar kv liftedTypeKind - | tyVarKind kv `eqKind` superBoxity = putTcTyVar kv liftedBoxity - | otherwise = pprPanic "zonkKindEnv" (ppr kv) + zonk_unbound_kind_var kv + | tyVarKind kv `eqKind` superKind = putTcTyVar kv liftedTypeKind + | 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 - -- Void if it has kind Lifted - -- :Void otherwise - -- 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 - | kind `eqKind` liftedTypeKind || kind `eqKind` openTypeKind - = putTcTyVar tv voidTy -- Just to avoid creating a new tycon in - -- this vastly common case - | otherwise - = putTcTyVar tv (TyConApp (mk_void_tycon tv kind) []) - where - kind = tyVarKind tv - - mk_void_tycon tv kind -- Make a new TyCon with the same kind as the - -- type variable tv. Same name too, 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. - = pprTrace "Urk! Inventing strangely-kinded void TyCon" (ppr tc_name) $ - mkPrimTyCon tc_name kind 0 [] VoidRep - where - tc_name = mkLocalName (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. @@ -435,7 +337,7 @@ zonkTcTypeToType ty = zonkType zonk_unbound_tyvar ty -- 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 @@ -448,13 +350,47 @@ 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. + %************************************************************************ %* * @@ -471,62 +407,62 @@ 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 (NewTcApp tycon tys) = mappM go tys `thenM` \ tys' -> + returnM (NewTcApp 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 (PredTy p) = go_pred p `thenM` \ p' -> + returnM (PredTy 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 (UsageTy u ty) = go u `thenNF_Tc` \ u' -> - go ty `thenNF_Tc` \ ty' -> - returnNF_Tc (UsageTy u' ty') + 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. -- 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 (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 @@ -582,6 +518,7 @@ data UserTypeCtxt -- f x :: t = .... | ForSigCtxt Name -- Foreign inport or export signature | RuleSigCtxt Name -- Signature on a forall'd variable in a RULE + | DefaultDeclCtxt -- Types in a default declaration -- Notes re TySynCtxt -- We allow type synonyms that aren't types; e.g. type List = [] @@ -594,28 +531,37 @@ data UserTypeCtxt -- With gla-exts that's right, but for H98 we should complain. -pprUserTypeCtxt (FunSigCtxt n) = ptext SLIT("the type signature for") <+> quotes (ppr n) -pprUserTypeCtxt ExprSigCtxt = ptext SLIT("an expression type signature") -pprUserTypeCtxt (ConArgCtxt c) = ptext SLIT("the type of constructor") <+> quotes (ppr c) -pprUserTypeCtxt (TySynCtxt c) = ptext SLIT("the RHS of a type synonym declaration") <+> quotes (ppr c) -pprUserTypeCtxt GenPatCtxt = ptext SLIT("the type pattern of a generic definition") -pprUserTypeCtxt PatSigCtxt = ptext SLIT("a pattern type signature") -pprUserTypeCtxt ResSigCtxt = ptext SLIT("a result type signature") -pprUserTypeCtxt (ForSigCtxt n) = ptext SLIT("the foreign signature for") <+> quotes (ppr n) -pprUserTypeCtxt (RuleSigCtxt n) = ptext SLIT("the type signature on") <+> quotes (ppr n) +pprHsSigCtxt :: UserTypeCtxt -> LHsType Name -> SDoc +pprHsSigCtxt ctxt hs_ty = pprUserTypeCtxt (unLoc hs_ty) ctxt + +pprUserTypeCtxt ty (FunSigCtxt n) = sep [ptext SLIT("In the type signature:"), pp_sig n ty] +pprUserTypeCtxt ty ExprSigCtxt = sep [ptext SLIT("In an expression type signature:"), nest 2 (ppr ty)] +pprUserTypeCtxt ty (ConArgCtxt c) = sep [ptext SLIT("In the type of the constructor"), pp_sig c ty] +pprUserTypeCtxt ty (TySynCtxt c) = sep [ptext SLIT("In the RHS of the type synonym") <+> quotes (ppr c) <> comma, + nest 2 (ptext SLIT(", namely") <+> ppr ty)] +pprUserTypeCtxt ty GenPatCtxt = sep [ptext SLIT("In the type pattern of a generic definition:"), nest 2 (ppr ty)] +pprUserTypeCtxt ty PatSigCtxt = sep [ptext SLIT("In a pattern type signature:"), nest 2 (ppr ty)] +pprUserTypeCtxt ty ResSigCtxt = sep [ptext SLIT("In a result type signature:"), nest 2 (ppr ty)] +pprUserTypeCtxt ty (ForSigCtxt n) = sep [ptext SLIT("In the foreign declaration:"), pp_sig n ty] +pprUserTypeCtxt ty (RuleSigCtxt n) = sep [ptext SLIT("In the type signature:"), pp_sig n ty] +pprUserTypeCtxt ty DefaultDeclCtxt = sep [ptext SLIT("In a type in a `default' declaration:"), nest 2 (ppr ty)] + +pp_sig n ty = nest 2 (ppr n <+> dcolon <+> ppr ty) \end{code} \begin{code} checkValidType :: UserTypeCtxt -> Type -> TcM () -- Checks that the type is valid for the given context checkValidType ctxt ty - = doptsTc Opt_GlasgowExts `thenNF_Tc` \ gla_exts -> + = traceTc (text "checkValidType" <+> ppr ty) `thenM_` + doptM Opt_GlasgowExts `thenM` \ gla_exts -> let rank | gla_exts = Arbitrary | otherwise = case ctxt of -- Haskell 98 GenPatCtxt -> Rank 0 PatSigCtxt -> Rank 0 + DefaultDeclCtxt-> Rank 0 ResSigCtxt -> Rank 0 TySynCtxt _ -> Rank 0 ExprSigCtxt -> Rank 1 @@ -634,32 +580,23 @@ checkValidType ctxt ty GenPatCtxt -> actual_kind_is_lifted ForSigCtxt _ -> actual_kind_is_lifted other -> isTypeKind actual_kind + + ubx_tup | not gla_exts = UT_NotOk + | otherwise = case ctxt of + TySynCtxt _ -> UT_Ok + ExprSigCtxt -> UT_Ok + other -> UT_NotOk + -- Unboxed tuples ok in function results, + -- but for type synonyms we allow them even at + -- top level in - tcAddErrCtxt (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 ty - - -checkTypeCtxt ctxt ty - = vcat [ptext SLIT("In the type:") <+> ppr_ty ty, - ptext SLIT("While checking") <+> pprUserTypeCtxt ctxt ] - - -- Hack alert. If there are no tyvars, (ppr sigma_ty) will print - -- something strange like {Eq k} -> k -> k, because there is no - -- ForAll at the top of the type. Since this is going to the user - -- we want it to look like a proper Haskell type even then; hence the hack - -- - -- 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 - | otherwise = ppr ty - where - (forall_tvs, theta, tau) = tcSplitSigmaTy ty + check_poly_type rank ubx_tup ty `thenM_` + + traceTc (text "checkValidType done" <+> ppr ty) \end{code} @@ -670,17 +607,23 @@ decRank :: Rank -> Rank decRank Arbitrary = Arbitrary decRank (Rank n) = Rank (n-1) -check_poly_type :: Rank -> Type -> TcM () -check_poly_type (Rank 0) ty - = check_tau_type (Rank 0) False ty +---------------------------------------- +data UbxTupFlag = UT_Ok | UT_NotOk + -- The "Ok" version means "ok if -fglasgow-exts is on" -check_poly_type rank ty +---------------------------------------- +check_poly_type :: Rank -> UbxTupFlag -> Type -> TcM () +check_poly_type (Rank 0) ubx_tup ty + = check_tau_type (Rank 0) ubx_tup ty + +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) False tau `thenTc_` - checkAmbiguity tvs theta tau + check_valid_theta SigmaCtxt theta `thenM_` + check_tau_type (decRank rank) ubx_tup tau `thenM_` + checkFreeness tvs theta `thenM_` + checkAmbiguity tvs theta (tyVarsOfType tau) ---------------------------------------- check_arg_type :: Type -> TcM () @@ -699,49 +642,79 @@ check_arg_type :: Type -> TcM () -- NB: unboxed tuples can have polymorphic or unboxed args. -- This happens in the workers for functions returning -- product types with polymorphic components. --- But not in user code --- --- Question: what about nested unboxed tuples? --- Currently rejected. +-- But not in user code. +-- Anyway, they are dealt with by a special case in check_tau_type + check_arg_type ty - = check_tau_type (Rank 0) False ty `thenTc_` + = check_tau_type (Rank 0) UT_NotOk ty `thenM_` checkTc (not (isUnLiftedType ty)) (unliftedArgErr ty) ---------------------------------------- -check_tau_type :: Rank -> Bool -> Type -> TcM () +check_tau_type :: Rank -> UbxTupFlag -> Type -> TcM () -- Rank is allowed rank for function args -- No foralls otherwise --- Bool is True iff unboxed tuple are allowed here - -check_tau_type rank ubx_tup_ok ty@(UsageTy _ _) = failWithTc (usageTyErr ty) -check_tau_type rank ubx_tup_ok ty@(ForAllTy _ _) = failWithTc (forAllTyErr ty) -check_tau_type rank ubx_tup_ok (SourceTy sty) = getDOptsTc `thenNF_Tc` \ dflags -> - check_source_ty dflags TypeCtxt sty -check_tau_type rank ubx_tup_ok (TyVarTy _) = returnTc () -check_tau_type rank ubx_tup_ok ty@(FunTy arg_ty res_ty) - = check_poly_type rank arg_ty `thenTc_` - check_tau_type rank True res_ty - -check_tau_type rank ubx_tup_ok (AppTy ty1 ty2) - = check_arg_type ty1 `thenTc_` check_arg_type ty2 - -check_tau_type rank ubx_tup_ok (NoteTy note ty) - = check_note note `thenTc_` check_tau_type rank ubx_tup_ok ty - -check_tau_type rank ubx_tup_ok ty@(TyConApp tc tys) - | isSynTyCon tc - = checkTc syn_arity_ok arity_msg `thenTc_` - mapTc_ check_arg_type tys + +check_tau_type rank ubx_tup ty@(ForAllTy _ _) = failWithTc (forAllTyErr ty) +check_tau_type rank ubx_tup (PredTy sty) = getDOpts `thenM` \ dflags -> + check_source_ty dflags TypeCtxt sty +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 `thenM_` + check_tau_type rank UT_Ok res_ty + +check_tau_type rank ubx_tup (AppTy ty1 ty2) + = check_arg_type ty1 `thenM_` check_arg_type ty2 + +check_tau_type rank ubx_tup (NoteTy (SynNote syn) ty) + -- Synonym notes are built only when the synonym is + -- saturated (see Type.mkSynTy) + = 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 (NewTcApp tc tys) + = mappM_ check_arg_type tys + +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) + -- to find the error + checkTc syn_arity_ok arity_msg `thenM_` + mappM_ check_arg_type tys | isUnboxedTupleTyCon tc - = checkTc ubx_tup_ok ubx_tup_msg `thenTc_` - mapTc_ (check_tau_type (Rank 0) True) tys -- Args are allowed to be unlifted, or - -- more unboxed tuples, so can't use check_arg_ty + = 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 } + syn_arity_ok = tc_arity <= n_args -- It's OK to have an *over-applied* type synonym -- data Tree a b = ... @@ -754,86 +727,13 @@ check_tau_type rank ubx_tup_ok ty@(TyConApp tc tys) ubx_tup_msg = ubxArgTyErr ty ---------------------------------------- -check_note (FTVNote _) = returnTc () -check_note (SynNote ty) = check_tau_type (Rank 0) False ty -\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 - -NOTE: 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. -This is the is_free test below. - -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 -> Type -> TcM () -checkAmbiguity forall_tyvars theta tau - = mapTc_ check_pred theta `thenTc_` - returnTc () - where - tau_vars = tyVarsOfType tau - extended_tau_vars = grow theta tau_vars - - is_ambig ct_var = (ct_var `elem` forall_tyvars) && - not (ct_var `elemVarSet` extended_tau_vars) - is_free ct_var = not (ct_var `elem` forall_tyvars) - - check_pred pred = checkTc (not any_ambig) (ambigErr pred) `thenTc_` - checkTc (isIPPred pred || not all_free) (freeErr pred) - where - ct_vars = varSetElems (tyVarsOfPred pred) - all_free = all is_free ct_vars - any_ambig = any is_ambig ct_vars +forAllTyErr ty = ptext SLIT("Illegal polymorphic type:") <+> ppr ty +unliftedArgErr ty = ptext SLIT("Illegal unlifted type argument:") <+> ppr ty +ubxArgTyErr ty = ptext SLIT("Illegal unboxed tuple type as function argument:") <+> ppr ty +kindErr kind = ptext SLIT("Expecting an ordinary type, but found a type of kind") <+> ppr kind \end{code} -\begin{code} -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 '=>'"))] - - -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")) - ] -forAllTyErr ty = ptext SLIT("Illegal polymorphic type:") <+> ppr_ty ty -usageTyErr ty = ptext SLIT("Illegal usage type:") <+> ppr_ty ty -unliftedArgErr ty = ptext SLIT("Illegal unlifted type argument:") <+> ppr_ty ty -ubxArgTyErr ty = ptext SLIT("Illegal unboxed tuple type as function argument:") <+> ppr_ty ty -kindErr kind = ptext SLIT("Expecting an ordinary type, but found a type of kind") <+> ppr kind -\end{code} %************************************************************************ %* * @@ -842,13 +742,25 @@ kindErr kind = ptext SLIT("Expecting an ordinary type, but found a type of %************************************************************************ \begin{code} +-- Enumerate the contexts in which a "source type", , can occur +-- Eq a +-- or ?x::Int +-- or r <: {x::Int} +-- or (N a) where N is a newtype + data SourceTyCtxt = ClassSCCtxt Name -- Superclasses of clas - | SigmaCtxt -- Context of a normal for-all type - | DataTyCtxt Name -- Context of a data decl + -- class => C a where ... + | SigmaCtxt -- Theta part of a normal for-all type + -- f :: => a -> a + | DataTyCtxt Name -- Theta part of a data decl + -- data => T a = MkT a | TypeCtxt -- Source type in an ordinary type + -- f :: N a -> N a | InstThetaCtxt -- Context of an instance decl + -- instance => C [a] where ... | InstHeadCtxt -- Head of an instance decl + -- instance ... => Eq a where ... pprSourceTyCtxt (ClassSCCtxt c) = ptext SLIT("the super-classes of class") <+> quotes (ppr c) pprSourceTyCtxt SigmaCtxt = ptext SLIT("the context of a polymorphic type") @@ -861,24 +773,30 @@ 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 TcHsType.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) + checkTc (arity == n_tys) arity_err `thenM_` + + -- Check the form of the argument types + mappM_ check_arg_type tys `thenM_` + checkTc (check_class_pred_tys dflags ctxt tys) (predTyVarErr pred $$ how_to_allow) where @@ -887,12 +805,6 @@ 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 @@ -908,12 +820,21 @@ 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 - -- 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 tcIsTyVarTy 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 @@ -922,14 +843,98 @@ 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} +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} -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) +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") <+> pprPred 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} @@ -960,22 +965,13 @@ 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 - | -- CCALL CHECK - -- A user declaration of a CCallable/CReturnable instance - -- must be for a "boxed primitive" type. - (clas `hasKey` cCallableClassKey - && not (ccallable_type first_ty)) - || (clas `hasKey` cReturnableClassKey - && not (creturnable_type first_ty)) - = failWithTc (nonBoxedPrimCCallErr clas first_ty) - -- If GlasgowExts then check at least one isn't a type variable | dopt Opt_GlasgowExts dflags = check_tyvars dflags clas tys @@ -987,7 +983,7 @@ 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) @@ -995,17 +991,14 @@ check_inst_head dflags clas tys where (first_ty : _) = tys - ccallable_type ty = isFFIArgumentTy dflags PlayRisky ty - creturnable_type ty = isFFIImportResultTy dflags ty - head_shape_msg = parens (text "The instance type must be of form (T a b c)" $$ text "where T is not a synonym, and a,b,c are distinct type variables") 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") @@ -1018,10 +1011,4 @@ undecidableMsg = ptext SLIT("Use -fallow-undecidable-instances to permit this") instTypeErr pp_ty msg = sep [ptext SLIT("Illegal instance declaration for") <+> quotes pp_ty, nest 4 msg] - -nonBoxedPrimCCallErr clas inst_ty - = hang (ptext SLIT("Unacceptable instance type for ccall-ish class")) - 4 (pprClassPred clas [inst_ty]) \end{code} - -