X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=ghc%2Fcompiler%2Ftypecheck%2FTcMonoType.lhs;h=93083908da7b118bcbc36b155112ca205a0fc874;hb=d68887047bcfb9021151f768fe1a22df2d3fbe1e;hp=a20c4603490d5f32cd1f59e151dd57b6db43f4d3;hpb=12b5aeae95e8d2bfa057157c8f02f6c186f4adec;p=ghc-hetmet.git diff --git a/ghc/compiler/typecheck/TcMonoType.lhs b/ghc/compiler/typecheck/TcMonoType.lhs index a20c460..9308390 100644 --- a/ghc/compiler/typecheck/TcMonoType.lhs +++ b/ghc/compiler/typecheck/TcMonoType.lhs @@ -4,54 +4,269 @@ \section[TcMonoType]{Typechecking user-specified @MonoTypes@} \begin{code} -module TcMonoType ( tcHsType, tcHsTypeKind, tcHsTopType, tcHsTopBoxedType, - tcContext, tcHsTyVar, kcHsTyVar, - tcExtendTyVarScope, tcExtendTopTyVarScope, - TcSigInfo(..), tcTySig, mkTcSig, noSigs, maybeSig, +module TcMonoType ( tcHsType, tcHsRecType, tcIfaceType, + tcHsSigType, tcHsLiftedSigType, + tcRecTheta, checkAmbiguity, + + -- Kind checking + kcHsTyVar, kcHsTyVars, mkTyClTyVars, + kcHsType, kcHsSigType, kcHsLiftedSigType, kcHsContext, + tcTyVars, tcHsTyVars, mkImmutTyVars, + + TcSigInfo(..), tcTySig, mkTcSig, maybeSig, checkSigTyVars, sigCtxt, sigPatCtxt ) where #include "HsVersions.h" -import HsSyn ( HsType(..), HsTyVar(..), Sig(..), pprClassAssertion, pprParendHsType ) -import RnHsSyn ( RenamedHsType, RenamedContext, RenamedSig ) +import HsSyn ( HsType(..), HsTyVarBndr(..), + Sig(..), HsPred(..), pprParendHsType, HsTupCon(..), hsTyVarNames ) +import RnHsSyn ( RenamedHsType, RenamedHsPred, RenamedContext, RenamedSig ) import TcHsSyn ( TcId ) import TcMonad -import TcEnv ( tcExtendTyVarEnv, tcLookupTy, tcGetValueEnv, tcGetInScopeTyVars, - tcGetGlobalTyVars, TcTyThing(..) +import TcEnv ( tcExtendTyVarEnv, tcLookup, tcLookupGlobal, + tcGetGlobalTyVars, tcEnvTcIds, tcEnvTyVars, + TyThing(..), TcTyThing(..), tcExtendKindEnv ) -import TcType ( TcType, TcKind, TcTyVar, TcThetaType, TcTauType, - typeToTcType, kindToTcKind, +import TcType ( TcKind, TcTyVar, TcThetaType, TcTauType, newKindVar, tcInstSigVar, - zonkTcKindToKind, zonkTcTypeToType, zonkTcTyVars, zonkTcType + zonkKindEnv, zonkTcType, zonkTcTyVars, zonkTcTyVar ) -import Inst ( Inst, InstOrigin(..), newMethodWithGivenTy, instToIdBndr ) -import TcUnify ( unifyKind, unifyKinds, unifyTypeKind ) -import Type ( Type, ThetaType, - mkTyVarTy, mkTyVarTys, mkFunTy, mkSynTy, zipFunTys, - mkSigmaTy, mkDictTy, mkTyConApp, mkAppTys, splitForAllTys, splitRhoTy, - boxedTypeKind, unboxedTypeKind, tyVarsOfType, - mkArrowKinds, getTyVar_maybe, getTyVar, - tidyOpenType, tidyOpenTypes, tidyTyVar, fullSubstTy +import Inst ( Inst, InstOrigin(..), newMethodWithGivenTy, instToId ) +import FunDeps ( grow ) +import TcUnify ( unifyKind, unifyOpenTypeKind ) +import Unify ( allDistinctTyVars ) +import Type ( Type, Kind, PredType(..), ThetaType, SigmaType, TauType, + mkTyVarTy, mkTyVarTys, mkFunTy, mkSynTy, + zipFunTys, hoistForAllTys, + mkSigmaTy, mkPredTy, mkTyConApp, + mkAppTys, splitForAllTys, splitRhoTy, mkRhoTy, + liftedTypeKind, unliftedTypeKind, mkArrowKind, + mkArrowKinds, getTyVar_maybe, getTyVar, splitFunTy_maybe, + tidyOpenType, tidyOpenTypes, tidyTyVar, tidyTyVars, + tyVarsOfType, tyVarsOfPred, mkForAllTys, + isUnboxedTupleType, isForAllTy, isIPPred ) -import Id ( mkUserId, idName, idType, idFreeTyVars ) -import Var ( TyVar, mkTyVar ) +import PprType ( pprType, pprTheta, pprPred ) +import Subst ( mkTopTyVarSubst, substTy ) +import CoreFVs ( idFreeTyVars ) +import Id ( mkLocalId, idName, idType ) +import Var ( Id, Var, TyVar, mkTyVar, tyVarKind ) import VarEnv import VarSet -import Bag ( bagToList ) import ErrUtils ( Message ) -import PrelInfo ( cCallishClassKeys ) -import TyCon ( TyCon ) -import Name ( Name, OccName, isLocallyDefined ) -import TysWiredIn ( mkListTy, mkTupleTy, mkUnboxedTupleTy ) +import TyCon ( TyCon, isSynTyCon, tyConArity, tyConKind ) +import Class ( classArity, classTyCon ) +import Name ( Name ) +import TysWiredIn ( mkListTy, mkTupleTy, genUnitTyCon ) +import BasicTypes ( Boxity(..), RecFlag(..), isRec ) import SrcLoc ( SrcLoc ) -import Unique ( Unique, Uniquable(..) ) -import UniqFM ( eltsUFM ) -import Util ( zipWithEqual, zipLazy, mapAccumL ) +import Util ( mapAccumL, isSingleton ) import Outputable + +\end{code} + + +%************************************************************************ +%* * +\subsection{Kind checking} +%* * +%************************************************************************ + +Kind checking +~~~~~~~~~~~~~ +When we come across the binding site for some type variables, we +proceed in two stages + +1. Figure out what kind each tyvar has + +2. Create suitably-kinded tyvars, + extend the envt, + and typecheck the body + +To do step 1, we proceed thus: + +1a. Bind each type variable to a kind variable +1b. Apply the kind checker +1c. Zonk the resulting kinds + +The kind checker is passed to tcHsTyVars as an argument. + +For example, when we find + (forall a m. m a -> m a) +we bind a,m to kind varibles and kind-check (m a -> m a). This +makes a get kind *, and m get kind *->*. Now we typecheck (m a -> m a) +in an environment that binds a and m suitably. + +The kind checker passed to tcHsTyVars needs to look at enough to +establish the kind of the tyvar: + * For a group of type and class decls, it's just the group, not + the rest of the program + * For a tyvar bound in a pattern type signature, its the types + mentioned in the other type signatures in that bunch of patterns + * For a tyvar bound in a RULE, it's the type signatures on other + universally quantified variables in the rule + +Note that this may occasionally give surprising results. For example: + + data T a b = MkT (a b) + +Here we deduce a::*->*, b::*. +But equally valid would be + a::(*->*)-> *, b::*->* + +\begin{code} +tcHsTyVars :: [HsTyVarBndr Name] + -> TcM a -- The kind checker + -> ([TyVar] -> TcM b) + -> TcM b + +tcHsTyVars [] kind_check thing_inside = thing_inside [] + -- A useful short cut for a common case! + +tcHsTyVars tv_names kind_check thing_inside + = kcHsTyVars tv_names `thenNF_Tc` \ tv_names_w_kinds -> + tcExtendKindEnv tv_names_w_kinds kind_check `thenTc_` + zonkKindEnv tv_names_w_kinds `thenNF_Tc` \ tvs_w_kinds -> + let + tyvars = mkImmutTyVars tvs_w_kinds + in + tcExtendTyVarEnv tyvars (thing_inside tyvars) + +tcTyVars :: [Name] + -> TcM a -- The kind checker + -> TcM [TyVar] +tcTyVars [] kind_check = returnTc [] + +tcTyVars tv_names kind_check + = mapNF_Tc newNamedKindVar tv_names `thenTc` \ kind_env -> + tcExtendKindEnv kind_env kind_check `thenTc_` + zonkKindEnv kind_env `thenNF_Tc` \ tvs_w_kinds -> + listNF_Tc [tcNewSigTyVar name kind | (name,kind) <- tvs_w_kinds] \end{code} + + +\begin{code} +kcHsTyVar :: HsTyVarBndr name -> NF_TcM (name, TcKind) +kcHsTyVars :: [HsTyVarBndr name] -> NF_TcM [(name, TcKind)] + +kcHsTyVar (UserTyVar name) = newNamedKindVar name +kcHsTyVar (IfaceTyVar name kind) = returnNF_Tc (name, kind) + +kcHsTyVars tvs = mapNF_Tc kcHsTyVar tvs + +newNamedKindVar name = newKindVar `thenNF_Tc` \ kind -> + returnNF_Tc (name, kind) +--------------------------- +kcLiftedType :: RenamedHsType -> TcM () + -- The type ty must be a *lifted* *type* +kcLiftedType ty + = kcHsType ty `thenTc` \ kind -> + tcAddErrCtxt (typeKindCtxt ty) $ + unifyKind liftedTypeKind kind + +--------------------------- +kcTypeType :: RenamedHsType -> TcM () + -- The type ty must be a *type*, but it can be lifted or unlifted. +kcTypeType ty + = kcHsType ty `thenTc` \ kind -> + tcAddErrCtxt (typeKindCtxt ty) $ + unifyOpenTypeKind kind + +--------------------------- +kcHsSigType, kcHsLiftedSigType :: RenamedHsType -> TcM () + -- Used for type signatures +kcHsSigType = kcTypeType +kcHsLiftedSigType = kcLiftedType + +--------------------------- +kcHsType :: RenamedHsType -> TcM TcKind +kcHsType (HsTyVar name) = kcTyVar name + +kcHsType (HsListTy ty) + = kcLiftedType ty `thenTc` \ tau_ty -> + returnTc liftedTypeKind + +kcHsType (HsTupleTy (HsTupCon _ boxity _) tys) + = mapTc kcTypeType tys `thenTc_` + returnTc (case boxity of + Boxed -> liftedTypeKind + Unboxed -> unliftedTypeKind) + +kcHsType (HsFunTy ty1 ty2) + = kcTypeType ty1 `thenTc_` + kcTypeType ty2 `thenTc_` + returnTc liftedTypeKind + +kcHsType ty@(HsOpTy ty1 op ty2) + = kcTyVar op `thenTc` \ op_kind -> + kcHsType ty1 `thenTc` \ ty1_kind -> + kcHsType ty2 `thenTc` \ ty2_kind -> + tcAddErrCtxt (appKindCtxt (ppr ty)) $ + kcAppKind op_kind ty1_kind `thenTc` \ op_kind' -> + kcAppKind op_kind' ty2_kind + +kcHsType (HsPredTy pred) + = kcHsPred pred `thenTc_` + returnTc liftedTypeKind + +kcHsType ty@(HsAppTy ty1 ty2) + = kcHsType ty1 `thenTc` \ tc_kind -> + kcHsType ty2 `thenTc` \ arg_kind -> + tcAddErrCtxt (appKindCtxt (ppr ty)) $ + kcAppKind tc_kind arg_kind + +kcHsType (HsForAllTy (Just tv_names) context ty) + = kcHsTyVars tv_names `thenNF_Tc` \ kind_env -> + tcExtendKindEnv kind_env $ + kcHsContext context `thenTc_` + kcHsType ty `thenTc_` + returnTc liftedTypeKind + +--------------------------- +kcAppKind fun_kind arg_kind + = case splitFunTy_maybe fun_kind of + Just (arg_kind', res_kind) + -> unifyKind arg_kind arg_kind' `thenTc_` + returnTc res_kind + + Nothing -> newKindVar `thenNF_Tc` \ res_kind -> + unifyKind fun_kind (mkArrowKind arg_kind res_kind) `thenTc_` + returnTc res_kind + + +--------------------------- +kcHsContext ctxt = mapTc_ kcHsPred ctxt + +kcHsPred :: RenamedHsPred -> TcM () +kcHsPred pred@(HsIParam name ty) + = tcAddErrCtxt (appKindCtxt (ppr pred)) $ + kcLiftedType ty + +kcHsPred pred@(HsClassP cls tys) + = tcAddErrCtxt (appKindCtxt (ppr pred)) $ + kcClass cls `thenTc` \ kind -> + mapTc kcHsType tys `thenTc` \ arg_kinds -> + unifyKind kind (mkArrowKinds arg_kinds liftedTypeKind) + + --------------------------- +kcTyVar name -- Could be a tyvar or a tycon + = tcLookup name `thenTc` \ thing -> + case thing of + AThing kind -> returnTc kind + ATyVar tv -> returnTc (tyVarKind tv) + AGlobal (ATyCon tc) -> returnTc (tyConKind tc) + other -> failWithTc (wrongThingErr "type" thing name) + +kcClass cls -- Must be a class + = tcLookup cls `thenNF_Tc` \ thing -> + case thing of + AThing kind -> returnTc kind + AGlobal (AClass cls) -> returnTc (tyConKind (classTyCon cls)) + other -> failWithTc (wrongThingErr "class" thing cls) +\end{code} %************************************************************************ %* * @@ -59,216 +274,320 @@ import Outputable %* * %************************************************************************ -tcHsType and tcHsTypeKind -~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +tcHsSigType and tcHsLiftedSigType +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +tcHsSigType and tcHsLiftedSigType are used for type signatures written by the programmer + + * We hoist any inner for-alls to the top -tcHsType checks that the type really is of kind Type! + * Notice that we kind-check first, because the type-check assumes + that the kinds are already checked. + + * They are only called when there are no kind vars in the environment + so the kind returned is indeed a Kind not a TcKind \begin{code} -tcHsType :: RenamedHsType -> TcM s TcType -tcHsType ty - = -- tcAddErrCtxt (typeCtxt ty) $ - tc_type ty - -tcHsTypeKind :: RenamedHsType -> TcM s (TcKind, TcType) -tcHsTypeKind ty - = -- tcAddErrCtxt (typeCtxt ty) $ - tc_type_kind ty - --- Type-check a type, *and* then lazily zonk it. The important --- point is that this zonks all the uncommitted *kind* variables --- in kinds of any any nested for-all tyvars. --- There won't be any mutable *type* variables at all. --- --- NOTE the forkNF_Tc. This makes the zonking lazy, which is --- absolutely necessary. During the type-checking of a recursive --- group of tycons/classes (TcTyClsDecls.tcGroup) we use an --- environment in which we aren't allowed to look at the actual --- tycons/classes returned from a lookup. Because tc_app does --- look at the tycon to build the type, we can't look at the type --- either, until we get out of the loop. The fork delays the --- zonking till we've completed the loop. Sigh. - -tcHsTopType :: RenamedHsType -> TcM s Type -tcHsTopType ty - = -- tcAddErrCtxt (typeCtxt ty) $ - tc_type ty `thenTc` \ ty' -> - forkNF_Tc (zonkTcTypeToType ty') - -tcHsTopBoxedType :: RenamedHsType -> TcM s Type -tcHsTopBoxedType ty - = -- tcAddErrCtxt (typeCtxt ty) $ - tc_boxed_type ty `thenTc` \ ty' -> - forkNF_Tc (zonkTcTypeToType ty') +tcHsSigType, tcHsLiftedSigType :: RenamedHsType -> TcM Type + -- Do kind checking, and hoist for-alls to the top +tcHsSigType ty = kcTypeType ty `thenTc_` tcHsType ty +tcHsLiftedSigType ty = kcLiftedType ty `thenTc_` tcHsType ty + +tcHsType :: RenamedHsType -> TcM Type +tcHsRecType :: RecFlag -> RenamedHsType -> TcM Type + -- Don't do kind checking, but do hoist for-alls to the top + -- These are used in type and class decls, where kinding is + -- done in advance +tcHsType ty = tc_type NonRecursive ty `thenTc` \ ty' -> returnTc (hoistForAllTys ty') +tcHsRecType wimp_out ty = tc_type wimp_out ty `thenTc` \ ty' -> returnTc (hoistForAllTys ty') + +-- In interface files the type is already kinded, +-- and we definitely don't want to hoist for-alls. +-- Otherwise we'll change +-- dmfail :: forall m:(*->*) Monad m => forall a:* => String -> m a +-- into +-- dmfail :: forall m:(*->*) a:* Monad m => String -> m a +-- which definitely isn't right! +tcIfaceType ty = tc_type NonRecursive ty \end{code} -The main work horse -~~~~~~~~~~~~~~~~~~~ +%************************************************************************ +%* * +\subsection{tc_type} +%* * +%************************************************************************ + +tc_type, the main work horse +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + + ------------------- + *** BIG WARNING *** + ------------------- + +tc_type is used to typecheck the types in the RHS of data +constructors. In the case of recursive data types, that means that +the type constructors themselves are (partly) black holes. e.g. + + data T a = MkT a [T a] + +While typechecking the [T a] on the RHS, T itself is not yet fully +defined. That in turn places restrictions on what you can check in +tcHsType; if you poke on too much you get a black hole. I keep +forgetting this, hence this warning! + +The wimp_out argument tells when we are in a mutually-recursive +group of type declarations, so omit various checks else we +get a black hole. They'll be done again later, in TcTyClDecls.tcGroup. + + -------------------------- + *** END OF BIG WARNING *** + -------------------------- + \begin{code} -tc_boxed_type :: RenamedHsType -> TcM s Type -tc_boxed_type ty - = tc_type_kind ty `thenTc` \ (actual_kind, tc_ty) -> - tcAddErrCtxt (typeKindCtxt ty) - (unifyKind boxedTypeKind actual_kind) `thenTc_` - returnTc tc_ty - -tc_type :: RenamedHsType -> TcM s Type -tc_type ty - -- The type ty must be a *type*, but it can be boxed - -- or unboxed. So we check that is is of form (Type bv) - -- using unifyTypeKind - = tc_type_kind ty `thenTc` \ (actual_kind, tc_ty) -> - tcAddErrCtxt (typeKindCtxt ty) - (unifyTypeKind actual_kind) `thenTc_` - returnTc tc_ty - -tc_type_kind :: RenamedHsType -> TcM s (TcKind, Type) -tc_type_kind ty@(MonoTyVar name) - = tc_app ty [] - -tc_type_kind (MonoListTy ty) - = tc_boxed_type ty `thenTc` \ tau_ty -> - returnTc (boxedTypeKind, mkListTy tau_ty) - -tc_type_kind (MonoTupleTy tys True {-boxed-}) - = mapTc tc_boxed_type tys `thenTc` \ tau_tys -> - returnTc (boxedTypeKind, mkTupleTy (length tys) tau_tys) - -tc_type_kind (MonoTupleTy tys False {-unboxed-}) - = mapTc tc_type tys `thenTc` \ tau_tys -> - returnTc (unboxedTypeKind, mkUnboxedTupleTy (length tys) tau_tys) - -tc_type_kind (MonoFunTy ty1 ty2) - = tc_type ty1 `thenTc` \ tau_ty1 -> - tc_type ty2 `thenTc` \ tau_ty2 -> - returnTc (boxedTypeKind, mkFunTy tau_ty1 tau_ty2) - -tc_type_kind (MonoTyApp ty1 ty2) - = tc_app ty1 [ty2] - -tc_type_kind (MonoDictTy class_name tys) - = tcClassAssertion (class_name, tys) `thenTc` \ (clas, arg_tys) -> - returnTc (boxedTypeKind, mkDictTy clas arg_tys) - -tc_type_kind (HsForAllTy (Just tv_names) context ty) - = tcExtendTyVarScope tv_names $ \ tyvars -> - tcContext context `thenTc` \ theta -> - case theta of - [] -> -- No context, so propagate body type - tc_type_kind ty `thenTc` \ (kind, tau) -> - returnTc (kind, mkSigmaTy tyvars [] tau) - - other -> -- Context; behave like a function type - -- This matters. Return-unboxed-tuple analysis can - -- give overloaded functions like - -- f :: forall a. Num a => (# a->a, a->a #) - -- And we want these to get through the type checker - - tc_type ty `thenTc` \ tau -> - returnTc (boxedTypeKind, mkSigmaTy tyvars theta tau) +tc_type :: RecFlag -> RenamedHsType -> TcM Type + +tc_type wimp_out ty@(HsTyVar name) + = tc_app wimp_out ty [] + +tc_type wimp_out (HsListTy ty) + = tc_arg_type wimp_out ty `thenTc` \ tau_ty -> + returnTc (mkListTy tau_ty) + +tc_type wimp_out (HsTupleTy (HsTupCon _ boxity arity) tys) + = ASSERT( arity == length tys ) + mapTc tc_tup_arg tys `thenTc` \ tau_tys -> + returnTc (mkTupleTy boxity arity tau_tys) + where + tc_tup_arg = case boxity of + Boxed -> tc_arg_type wimp_out + Unboxed -> tc_type wimp_out + -- Unboxed tuples can have polymorphic or unboxed args. + -- This happens in the workers for functions returning + -- product types with polymorphic components + +tc_type wimp_out (HsFunTy ty1 ty2) + = tc_type wimp_out ty1 `thenTc` \ tau_ty1 -> + -- Function argument can be polymorphic, but + -- must not be an unboxed tuple + checkTc (not (isUnboxedTupleType tau_ty1)) + (ubxArgTyErr ty1) `thenTc_` + tc_type wimp_out ty2 `thenTc` \ tau_ty2 -> + returnTc (mkFunTy tau_ty1 tau_ty2) + +tc_type wimp_out (HsNumTy n) + = ASSERT(n== 1) + returnTc (mkTyConApp genUnitTyCon []) + +tc_type wimp_out (HsOpTy ty1 op ty2) = + tc_arg_type wimp_out ty1 `thenTc` \ tau_ty1 -> + tc_arg_type wimp_out ty2 `thenTc` \ tau_ty2 -> + tc_fun_type op [tau_ty1,tau_ty2] + +tc_type wimp_out (HsAppTy ty1 ty2) + = tc_app wimp_out ty1 [ty2] + +tc_type wimp_out (HsPredTy pred) + = tc_pred wimp_out pred `thenTc` \ pred' -> + returnTc (mkPredTy pred') + +tc_type wimp_out full_ty@(HsForAllTy (Just tv_names) ctxt ty) + = let + kind_check = kcHsContext ctxt `thenTc_` kcHsType ty + in + tcHsTyVars tv_names kind_check $ \ tyvars -> + tcRecTheta wimp_out ctxt `thenTc` \ theta -> + + -- Context behaves like a function type + -- This matters. Return-unboxed-tuple analysis can + -- give overloaded functions like + -- f :: forall a. Num a => (# a->a, a->a #) + -- And we want these to get through the type checker + (if null theta then + tc_arg_type wimp_out ty + else + tc_type wimp_out ty + ) `thenTc` \ tau -> + + checkAmbiguity wimp_out is_source tyvars theta tau + where + is_source = case tv_names of + (UserTyVar _ : _) -> True + other -> False + + + -- tc_arg_type checks that the argument of a + -- type appplication isn't a for-all type or an unboxed tuple type + -- For example, we want to reject things like: + -- + -- instance Ord a => Ord (forall s. T s a) + -- and + -- g :: T s (forall b.b) + -- + -- Other unboxed types are very occasionally allowed as type + -- arguments depending on the kind of the type constructor + +tc_arg_type wimp_out arg_ty + | isRec wimp_out + = tc_type wimp_out arg_ty + + | otherwise + = tc_type wimp_out arg_ty `thenTc` \ arg_ty' -> + checkTc (not (isForAllTy arg_ty')) (polyArgTyErr arg_ty) `thenTc_` + checkTc (not (isUnboxedTupleType arg_ty')) (ubxArgTyErr arg_ty) `thenTc_` + returnTc arg_ty' + +tc_arg_types wimp_out arg_tys = mapTc (tc_arg_type wimp_out) arg_tys \end{code} Help functions for type applications ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ \begin{code} -tc_app (MonoTyApp ty1 ty2) tys - = tc_app ty1 (ty2:tys) - -tc_app ty tys - | null tys - = tc_fun_type ty [] +tc_app :: RecFlag -> RenamedHsType -> [RenamedHsType] -> TcM Type +tc_app wimp_out (HsAppTy ty1 ty2) tys + = tc_app wimp_out ty1 (ty2:tys) - | otherwise +tc_app wimp_out ty tys = tcAddErrCtxt (appKindCtxt pp_app) $ - mapAndUnzipTc tc_type_kind tys `thenTc` \ (arg_kinds, arg_tys) -> - tc_fun_type ty arg_tys `thenTc` \ (fun_kind, result_ty) -> - - -- Check argument compatibility - newKindVar `thenNF_Tc` \ result_kind -> - unifyKind fun_kind (mkArrowKinds arg_kinds result_kind) - `thenTc_` - returnTc (result_kind, result_ty) + tc_arg_types wimp_out tys `thenTc` \ arg_tys -> + case ty of + HsTyVar fun -> tc_fun_type fun arg_tys + other -> tc_type wimp_out ty `thenTc` \ fun_ty -> + returnNF_Tc (mkAppTys fun_ty arg_tys) where pp_app = ppr ty <+> sep (map pprParendHsType tys) --- (tc_fun_type ty arg_tys) returns (kind-of ty, mkAppTys ty arg_tys) +-- (tc_fun_type ty arg_tys) returns (mkAppTys ty arg_tys) -- But not quite; for synonyms it checks the correct arity, and builds a SynTy -- hence the rather strange functionality. -tc_fun_type (MonoTyVar name) arg_tys - = tcLookupTy name `thenTc` \ (tycon_kind, maybe_arity, thing) -> +tc_fun_type name arg_tys + = tcLookup name `thenTc` \ thing -> case thing of - ATyVar tv -> returnTc (tycon_kind, mkAppTys (mkTyVarTy tv) arg_tys) - AClass clas -> failWithTc (classAsTyConErr name) - ATyCon tc -> case maybe_arity of - Nothing -> -- Data or newtype - returnTc (tycon_kind, mkTyConApp tc arg_tys) - - Just arity -> -- Type synonym - checkTc (arity <= n_args) err_msg `thenTc_` - returnTc (tycon_kind, result_ty) - where - -- It's OK to have an *over-applied* type synonym - -- data Tree a b = ... - -- type Foo a = Tree [a] - -- f :: Foo a b -> ... - result_ty = mkAppTys (mkSynTy tc (take arity arg_tys)) - (drop arity arg_tys) - err_msg = arityErr "type synonym" name arity n_args - n_args = length arg_tys - -tc_fun_type ty arg_tys - = tc_type_kind ty `thenTc` \ (fun_kind, fun_ty) -> - returnTc (fun_kind, mkAppTys fun_ty arg_tys) + ATyVar tv -> returnTc (mkAppTys (mkTyVarTy tv) arg_tys) + + AGlobal (ATyCon tc) + | isSynTyCon tc -> checkTc arity_ok err_msg `thenTc_` + returnTc (mkAppTys (mkSynTy tc (take arity arg_tys)) + (drop arity arg_tys)) + + | otherwise -> returnTc (mkTyConApp tc arg_tys) + where + + arity_ok = arity <= n_args + arity = tyConArity tc + -- It's OK to have an *over-applied* type synonym + -- data Tree a b = ... + -- type Foo a = Tree [a] + -- f :: Foo a b -> ... + err_msg = arityErr "Type synonym" name arity n_args + n_args = length arg_tys + + other -> failWithTc (wrongThingErr "type constructor" thing name) \end{code} Contexts ~~~~~~~~ \begin{code} - -tcContext :: RenamedContext -> TcM s ThetaType -tcContext context - = --Someone discovered that @CCallable@ and @CReturnable@ - -- could be used in contexts such as: - -- foo :: CCallable a => a -> PrimIO Int - -- Doing this utterly wrecks the whole point of introducing these - -- classes so we specifically check that this isn't being done. - -- - -- We *don't* do this check in tcClassAssertion, because that's - -- called when checking a HsDictTy, and we don't want to reject - -- instance CCallable Int - -- etc. Ugh! - mapTc check_naughty context `thenTc_` - - mapTc tcClassAssertion context - - where - check_naughty (class_name, _) - = checkTc (not (getUnique class_name `elem` cCallishClassKeys)) - (naughtyCCallContextErr class_name) - -tcClassAssertion assn@(class_name, tys) - = tcAddErrCtxt (appKindCtxt (pprClassAssertion assn)) $ - mapAndUnzipTc tc_type_kind tys `thenTc` \ (arg_kinds, arg_tys) -> - tcLookupTy class_name `thenTc` \ (kind, ~(Just arity), thing) -> +tcRecTheta :: RecFlag -> RenamedContext -> TcM ThetaType + -- Used when we are expecting a ClassContext (i.e. no implicit params) +tcRecTheta wimp_out context = mapTc (tc_pred wimp_out) context + +tc_pred wimp_out assn@(HsClassP class_name tys) + = tcAddErrCtxt (appKindCtxt (ppr assn)) $ + tc_arg_types wimp_out tys `thenTc` \ arg_tys -> + tcLookupGlobal class_name `thenTc` \ thing -> case thing of - ATyVar _ -> failWithTc (tyVarAsClassErr class_name) - ATyCon _ -> failWithTc (tyConAsClassErr class_name) - AClass clas -> - -- Check with kind mis-match - checkTc (arity == n_tys) err `thenTc_` - unifyKind kind (mkArrowKinds arg_kinds boxedTypeKind) `thenTc_` - returnTc (clas, arg_tys) + AClass clas -> checkTc (arity == n_tys) err `thenTc_` + returnTc (ClassP clas arg_tys) where + arity = classArity clas n_tys = length tys err = arityErr "Class" class_name arity n_tys + + other -> failWithTc (wrongThingErr "class" (AGlobal thing) class_name) + +tc_pred wimp_out assn@(HsIParam name ty) + = tcAddErrCtxt (appKindCtxt (ppr assn)) $ + tc_arg_type wimp_out ty `thenTc` \ arg_ty -> + returnTc (IParam name arg_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. + +Notes on the 'is_source_polytype' test above +Check ambiguity only for source-program 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 :: RecFlag -> Bool + -> [TyVar] -> ThetaType -> TauType + -> TcM SigmaType +checkAmbiguity wimp_out is_source_polytype forall_tyvars theta tau + | isRec wimp_out = returnTc sigma_ty + | otherwise = mapTc_ check_pred theta `thenTc_` + returnTc sigma_ty + where + sigma_ty = mkSigmaTy forall_tyvars theta tau + tau_vars = tyVarsOfType tau + extended_tau_vars = grow theta tau_vars + + -- 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_sigma | null forall_tyvars = pprTheta theta <+> ptext SLIT("=>") <+> ppr tau + | otherwise = ppr sigma_ty + + 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 ppr_sigma) `thenTc_` + checkTc (isIPPred pred || not all_free) (freeErr pred ppr_sigma) + where + ct_vars = varSetElems (tyVarsOfPred pred) + all_free = all is_free ct_vars + any_ambig = is_source_polytype && any is_ambig ct_vars +\end{code} + %************************************************************************ %* * \subsection{Type variables, with knot tying!} @@ -276,38 +595,16 @@ tcClassAssertion assn@(class_name, tys) %************************************************************************ \begin{code} -tcExtendTopTyVarScope :: TcKind -> [HsTyVar Name] - -> ([TcTyVar] -> TcKind -> TcM s a) - -> TcM s a -tcExtendTopTyVarScope kind tyvar_names thing_inside - = let - (tyvars_w_kinds, result_kind) = zipFunTys tyvar_names kind - tyvars = map mk_tv tyvars_w_kinds - in - tcExtendTyVarEnv tyvars (thing_inside tyvars result_kind) +mkImmutTyVars :: [(Name,Kind)] -> [TyVar] +mkImmutTyVars pairs = [mkTyVar name kind | (name, kind) <- pairs] + +mkTyClTyVars :: Kind -- Kind of the tycon or class + -> [HsTyVarBndr Name] + -> [TyVar] +mkTyClTyVars kind tyvar_names + = mkImmutTyVars tyvars_w_kinds where - mk_tv (UserTyVar name, kind) = mkTyVar name kind - mk_tv (IfaceTyVar name _, kind) = mkTyVar name kind - -- NB: immutable tyvars, but perhaps with mutable kinds - -tcExtendTyVarScope :: [HsTyVar Name] - -> ([TcTyVar] -> TcM s a) -> TcM s a -tcExtendTyVarScope tv_names thing_inside - = mapNF_Tc tcHsTyVar tv_names `thenNF_Tc` \ tyvars -> - tcExtendTyVarEnv tyvars $ - thing_inside tyvars - -tcHsTyVar :: HsTyVar Name -> NF_TcM s TcTyVar -tcHsTyVar (UserTyVar name) = newKindVar `thenNF_Tc` \ kind -> - tcNewMutTyVar name kind - -- NB: mutable kind => mutable tyvar, so that zonking can bind - -- the tyvar to its immutable form - -tcHsTyVar (IfaceTyVar name kind) = returnNF_Tc (mkTyVar name (kindToTcKind kind)) - -kcHsTyVar :: HsTyVar name -> NF_TcM s TcKind -kcHsTyVar (UserTyVar name) = newKindVar -kcHsTyVar (IfaceTyVar name kind) = returnNF_Tc (kindToTcKind kind) + (tyvars_w_kinds, _) = zipFunTys (hsTyVarNames tyvar_names) kind \end{code} @@ -342,11 +639,14 @@ data TcSigInfo -- Does *not* have name = N -- Has type tau - Inst -- Empty if theta is null, or + [Inst] -- Empty if theta is null, or -- (method mono_id) otherwise SrcLoc -- Of the signature +instance Outputable TcSigInfo where + ppr (TySigInfo nm id tyvars theta tau _ inst loc) = + ppr nm <+> ptext SLIT("::") <+> ppr tyvars <+> ppr theta <+> ptext SLIT("=>") <+> ppr tau maybeSig :: [TcSigInfo] -> Name -> Maybe (TcSigInfo) -- Search for a particular signature @@ -354,23 +654,20 @@ maybeSig [] name = Nothing maybeSig (sig@(TySigInfo sig_name _ _ _ _ _ _ _) : sigs) name | name == sig_name = Just sig | otherwise = maybeSig sigs name - --- This little helper is useful to pass to tcPat -noSigs :: Name -> Maybe TcId -noSigs name = Nothing \end{code} \begin{code} -tcTySig :: RenamedSig -> TcM s TcSigInfo +tcTySig :: RenamedSig -> TcM TcSigInfo tcTySig (Sig v ty src_loc) - = tcAddSrcLoc src_loc $ - tcHsType ty `thenTc` \ sigma_tc_ty -> - mkTcSig (mkUserId v sigma_tc_ty) src_loc `thenNF_Tc` \ sig -> + = tcAddSrcLoc src_loc $ + tcAddErrCtxt (tcsigCtxt v) $ + tcHsSigType ty `thenTc` \ sigma_tc_ty -> + mkTcSig (mkLocalId v sigma_tc_ty) src_loc `thenNF_Tc` \ sig -> returnTc sig -mkTcSig :: TcId -> SrcLoc -> NF_TcM s TcSigInfo +mkTcSig :: TcId -> SrcLoc -> NF_TcM TcSigInfo mkTcSig poly_id src_loc = -- Instantiate this type -- It's important to do this even though in the error-free case @@ -387,7 +684,8 @@ mkTcSig poly_id src_loc let tyvar_tys' = mkTyVarTys tyvars' - rho' = fullSubstTy (zipVarEnv tyvars tyvar_tys') emptyVarSet rho + rho' = substTy (mkTopTyVarSubst tyvars tyvar_tys') rho + -- mkTopTyVarSubst because the tyvars' are fresh (theta', tau') = splitRhoTy rho' -- This splitRhoTy tries hard to make sure that tau' is a type synonym -- wherever possible, which can improve interface files. @@ -398,7 +696,7 @@ mkTcSig poly_id src_loc theta' tau' `thenNF_Tc` \ inst -> -- We make a Method even if it's not overloaded; no harm - returnNF_Tc (TySigInfo name poly_id tyvars' theta' tau' (instToIdBndr inst) inst src_loc) + returnNF_Tc (TySigInfo name poly_id tyvars' theta' tau' (instToId inst) [inst] src_loc) where name = idName poly_id \end{code} @@ -468,34 +766,33 @@ So we revert to ordinary type variables for signatures, and try to give a helpful message in checkSigTyVars. \begin{code} -checkSigTyVars :: [TcTyVar] -- The original signature type variables - -> TcM s [TcTyVar] -- Zonked signature type variables - -checkSigTyVars [] = returnTc [] - -checkSigTyVars sig_tyvars +checkSigTyVars :: [TcTyVar] -- Universally-quantified type variables in the signature + -> TcTyVarSet -- Tyvars that are free in the type signature + -- Not necessarily zonked + -- These should *already* be in the free-in-env set, + -- and are used here only to improve the error message + -> TcM [TcTyVar] -- Zonked signature type variables + +checkSigTyVars [] free = returnTc [] +checkSigTyVars sig_tyvars free_tyvars = zonkTcTyVars sig_tyvars `thenNF_Tc` \ sig_tys -> tcGetGlobalTyVars `thenNF_Tc` \ globals -> - checkTcM (all_ok sig_tys globals) + checkTcM (allDistinctTyVars sig_tys globals) (complain sig_tys globals) `thenTc_` returnTc (map (getTyVar "checkSigTyVars") sig_tys) where - all_ok [] acc = True - all_ok (ty:tys) acc = case getTyVar_maybe ty of - Nothing -> False -- Point (a) - Just tv | tv `elemVarSet` acc -> False -- Point (b) or (c) - | otherwise -> all_ok tys (acc `extendVarSet` tv) - - complain sig_tys globals = -- For the in-scope ones, zonk them and construct a map -- from the zonked tyvar to the in-scope one -- If any of the in-scope tyvars zonk to a type, then ignore them; -- that'll be caught later when we back up to their type sig - tcGetInScopeTyVars `thenNF_Tc` \ in_scope_tvs -> + tcGetEnv `thenNF_Tc` \ env -> + let + in_scope_tvs = tcEnvTyVars env + in zonkTcTyVars in_scope_tvs `thenNF_Tc` \ in_scope_tys -> let in_scope_assoc = [ (zonked_tv, in_scope_tv) @@ -517,88 +814,128 @@ checkSigTyVars sig_tyvars main_msg = ptext SLIT("Inferred type is less polymorphic than expected") - check (env, acc, msgs) (sig_tyvar,ty) + check (tidy_env, acc, msgs) (sig_tyvar,ty) -- sig_tyvar is from the signature; -- ty is what you get if you zonk sig_tyvar and then tidy it -- -- acc maps a zonked type variable back to a signature type variable = case getTyVar_maybe ty of { Nothing -> -- Error (a)! - returnNF_Tc (env, acc, unify_msg sig_tyvar (ppr ty) : msgs) ; + returnNF_Tc (tidy_env, acc, unify_msg sig_tyvar (quotes (ppr ty)) : msgs) ; Just tv -> case lookupVarEnv acc tv of { Just sig_tyvar' -> -- Error (b) or (d)! - returnNF_Tc (env, acc, unify_msg sig_tyvar (ppr sig_tyvar') : msgs) ; + returnNF_Tc (tidy_env, acc, unify_msg sig_tyvar thing : msgs) + where + thing = ptext SLIT("another quantified type variable") <+> quotes (ppr sig_tyvar') - Nothing -> + ; Nothing -> if tv `elemVarSet` globals -- Error (c)! Type variable escapes -- The least comprehensible, so put it last - then tcGetValueEnv `thenNF_Tc` \ ve -> - find_globals tv env (eltsUFM ve) `thenNF_Tc` \ (env1, globs) -> - returnNF_Tc (env1, acc, escape_msg sig_tyvar tv globs : msgs) + -- Game plan: + -- a) get the local TcIds from the environment, + -- and pass them to find_globals (they might have tv free) + -- b) similarly, find any free_tyvars that mention tv + then tcGetEnv `thenNF_Tc` \ ve -> + find_globals tv tidy_env [] (tcEnvTcIds ve) `thenNF_Tc` \ (tidy_env1, globs) -> + find_frees tv tidy_env1 [] (varSetElems free_tyvars) `thenNF_Tc` \ (tidy_env2, frees) -> + returnNF_Tc (tidy_env2, acc, escape_msg sig_tyvar tv globs frees : msgs) else -- All OK - returnNF_Tc (env, extendVarEnv acc tv sig_tyvar, msgs) + returnNF_Tc (tidy_env, extendVarEnv acc tv sig_tyvar, msgs) }} -- find_globals looks at the value environment and finds values -- whose types mention the offending type variable. It has to be -- careful to zonk the Id's type first, so it has to be in the monad. -- We must be careful to pass it a zonked type variable, too. -find_globals tv tidy_env ids - | null ids - = returnNF_Tc (tidy_env, []) -find_globals tv tidy_env (id:ids) - | not (isLocallyDefined id) || - isEmptyVarSet (idFreeTyVars id) - = find_globals tv tidy_env ids +find_globals :: Var + -> TidyEnv + -> [(Name,Type)] + -> [Id] + -> NF_TcM (TidyEnv,[(Name,Type)]) + +find_globals tv tidy_env acc [] + = returnNF_Tc (tidy_env, acc) + +find_globals tv tidy_env acc (id:ids) + | isEmptyVarSet (idFreeTyVars id) + = find_globals tv tidy_env acc ids | otherwise = zonkTcType (idType id) `thenNF_Tc` \ id_ty -> if tv `elemVarSet` tyVarsOfType id_ty then let (tidy_env', id_ty') = tidyOpenType tidy_env id_ty + acc' = (idName id, id_ty') : acc in - find_globals tv tidy_env' ids `thenNF_Tc` \ (tidy_env'', globs) -> - returnNF_Tc (tidy_env'', (idName id, id_ty') : globs) + find_globals tv tidy_env' acc' ids else - find_globals tv tidy_env ids + find_globals tv tidy_env acc ids -escape_msg sig_tv tv globs - = vcat [mk_msg sig_tv <+> ptext SLIT("escapes"), - pp_escape, - ptext SLIT("The following variables in the environment mention") <+> quotes (ppr tv), - nest 4 (vcat_first 10 [ppr name <+> dcolon <+> ppr ty | (name,ty) <- globs]) - ] +find_frees tv tidy_env acc [] + = returnNF_Tc (tidy_env, acc) +find_frees tv tidy_env acc (ftv:ftvs) + = zonkTcTyVar ftv `thenNF_Tc` \ ty -> + if tv `elemVarSet` tyVarsOfType ty then + let + (tidy_env', ftv') = tidyTyVar tidy_env ftv + in + find_frees tv tidy_env' (ftv':acc) ftvs + else + find_frees tv tidy_env acc ftvs + + +escape_msg sig_tv tv globs frees + = mk_msg sig_tv <+> ptext SLIT("escapes") $$ + if not (null globs) then + vcat [pp_it <+> ptext SLIT("is mentioned in the environment"), + ptext SLIT("The following variables in the environment mention") <+> quotes (ppr tv), + nest 2 (vcat_first 10 [ppr name <+> dcolon <+> ppr ty | (name,ty) <- globs]) + ] + else if not (null frees) then + vcat [ptext SLIT("It is reachable from the type variable(s)") <+> pprQuotedList frees, + nest 2 (ptext SLIT("which") <+> is_are <+> ptext SLIT("free in the signature")) + ] + else + empty -- Sigh. It's really hard to give a good error message + -- all the time. One bad case is an existential pattern match where - pp_escape | sig_tv /= tv = ptext SLIT("It unifies with") <+> - quotes (ppr tv) <> comma <+> - ptext SLIT("which is mentioned in the environment") - | otherwise = ptext SLIT("It is mentioned in the environment") + is_are | isSingleton frees = ptext SLIT("is") + | otherwise = ptext SLIT("are") + pp_it | sig_tv /= tv = ptext SLIT("It unifies with") <+> quotes (ppr tv) <> comma <+> ptext SLIT("which") + | otherwise = ptext SLIT("It") vcat_first :: Int -> [SDoc] -> SDoc vcat_first n [] = empty vcat_first 0 (x:xs) = text "...others omitted..." vcat_first n (x:xs) = x $$ vcat_first (n-1) xs -unify_msg tv thing = mk_msg tv <+> ptext SLIT("is unified with") <+> quotes thing +unify_msg tv thing = mk_msg tv <+> ptext SLIT("is unified with") <+> thing mk_msg tv = ptext SLIT("Quantified type variable") <+> quotes (ppr tv) \end{code} These two context are used with checkSigTyVars \begin{code} -sigCtxt :: (Type -> Message) -> Type - -> TidyEnv -> NF_TcM s (TidyEnv, Message) -sigCtxt mk_msg sig_ty tidy_env - = let - (env1, tidy_sig_ty) = tidyOpenType tidy_env sig_ty +sigCtxt :: Message -> [TcTyVar] -> TcThetaType -> TcTauType + -> TidyEnv -> NF_TcM (TidyEnv, Message) +sigCtxt when sig_tyvars sig_theta sig_tau tidy_env + = zonkTcType sig_tau `thenNF_Tc` \ actual_tau -> + let + (env1, tidy_sig_tyvars) = tidyTyVars tidy_env sig_tyvars + (env2, tidy_sig_rho) = tidyOpenType env1 (mkRhoTy sig_theta sig_tau) + (env3, tidy_actual_tau) = tidyOpenType env2 actual_tau + msg = vcat [ptext SLIT("Signature type: ") <+> pprType (mkForAllTys tidy_sig_tyvars tidy_sig_rho), + ptext SLIT("Type to generalise:") <+> pprType tidy_actual_tau, + when + ] in - returnNF_Tc (env1, mk_msg tidy_sig_ty) + returnNF_Tc (env3, msg) sigPatCtxt bound_tvs bound_ids tidy_env = returnNF_Tc (env1, @@ -621,11 +958,7 @@ sigPatCtxt bound_tvs bound_ids tidy_env %************************************************************************ \begin{code} -naughtyCCallContextErr clas_name - = sep [ptext SLIT("Can't use class") <+> quotes (ppr clas_name), - ptext SLIT("in a context")] - -typeCtxt ty = ptext SLIT("In the type") <+> quotes (ppr ty) +tcsigCtxt v = ptext SLIT("In a type signature for") <+> quotes (ppr v) typeKindCtxt :: RenamedHsType -> Message typeKindCtxt ty = sep [ptext SLIT("When checking that"), @@ -635,12 +968,29 @@ typeKindCtxt ty = sep [ptext SLIT("When checking that"), appKindCtxt :: SDoc -> Message appKindCtxt pp = ptext SLIT("When checking kinds in") <+> quotes pp -classAsTyConErr name - = ptext SLIT("Class used as a type constructor:") <+> ppr name - -tyConAsClassErr name - = ptext SLIT("Type constructor used as a class:") <+> ppr name +wrongThingErr expected thing name + = pp_thing thing <+> quotes (ppr name) <+> ptext SLIT("used as a") <+> text expected + where + pp_thing (AGlobal (ATyCon _)) = ptext SLIT("Type constructor") + pp_thing (AGlobal (AClass _)) = ptext SLIT("Class") + pp_thing (AGlobal (AnId _)) = ptext SLIT("Identifier") + pp_thing (ATyVar _) = ptext SLIT("Type variable") + pp_thing (ATcId _) = ptext SLIT("Local identifier") + pp_thing (AThing _) = ptext SLIT("Utterly bogus") + +ambigErr pred ppr_ty + = sep [ptext SLIT("Ambiguous constraint") <+> quotes (pprPred pred), + nest 4 (ptext SLIT("for the type:") <+> ppr_ty), + 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 ppr_ty + = 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")), + ptext SLIT("In the type") <+> quotes ppr_ty + ] -tyVarAsClassErr name - = ptext SLIT("Type variable used as a class:") <+> ppr name +polyArgTyErr ty = ptext SLIT("Illegal polymorphic type as argument:") <+> ppr ty +ubxArgTyErr ty = ptext SLIT("Illegal unboxed tuple type as argument:") <+> ppr ty \end{code}