X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=ghc%2Fcompiler%2Ftypecheck%2FTcMonoType.lhs;h=cf1231524127c00d1dd72fb9a4059977ead2e405;hb=2205f0ceeb65d8acb7db953bf4fd2ad673dc55ee;hp=cb70d6a084051156b5466b15cbcf6ec12b9039e3;hpb=e7f04a0da2a711266b58274a1a935d93bb034620;p=ghc-hetmet.git diff --git a/ghc/compiler/typecheck/TcMonoType.lhs b/ghc/compiler/typecheck/TcMonoType.lhs index cb70d6a..cf12315 100644 --- a/ghc/compiler/typecheck/TcMonoType.lhs +++ b/ghc/compiler/typecheck/TcMonoType.lhs @@ -4,61 +4,57 @@ \section[TcMonoType]{Typechecking user-specified @MonoTypes@} \begin{code} -module TcMonoType ( tcHsType, tcHsSigType, tcHsTypeKind, tcHsTopType, tcHsTopBoxedType, tcHsTopTypeKind, - tcContext, tcHsTyVar, kcHsTyVar, kcHsType, - tcExtendTyVarScope, tcExtendTopTyVarScope, - TcSigInfo(..), tcTySig, mkTcSig, maybeSig, - checkSigTyVars, sigCtxt, sigPatCtxt +module TcMonoType ( tcHsSigType, tcHsType, tcIfaceType, tcHsTheta, tcHsPred, + UserTypeCtxt(..), + + -- Kind checking + kcHsTyVar, kcHsTyVars, mkTyClTyVars, + kcHsType, kcHsSigType, kcHsSigTypes, + kcHsLiftedSigType, kcHsContext, + tcAddScopedTyVars, tcHsTyVars, mkImmutTyVars, + + TcSigInfo(..), tcTySig, mkTcSig, maybeSig, tcSigPolyId, tcSigMonoId ) where #include "HsVersions.h" -import HsSyn ( HsType(..), HsTyVarBndr(..), HsUsageAnn(..), - Sig(..), HsPred(..), pprParendHsType, HsTupCon(..) ) -import RnHsSyn ( RenamedHsType, RenamedContext, RenamedSig ) +import HsSyn ( HsType(..), HsTyVarBndr(..), HsTyOp(..), + Sig(..), HsPred(..), pprParendHsType, HsTupCon(..), hsTyVarNames ) +import RnHsSyn ( RenamedHsType, RenamedHsPred, RenamedContext, RenamedSig, extractHsTyVars ) import TcHsSyn ( TcId ) import TcMonad -import TcEnv ( tcExtendTyVarEnv, tcLookupTy, tcGetValueEnv, tcGetInScopeTyVars, - tcExtendUVarEnv, tcLookupUVar, - tcGetGlobalTyVars, valueEnvIds, TcTyThing(..) +import TcEnv ( tcExtendTyVarEnv, tcLookup, tcLookupGlobal, + tcInLocalScope, + TyThing(..), TcTyThing(..), tcExtendKindEnv ) -import TcType ( TcType, TcKind, TcTyVar, TcThetaType, TcTauType, - typeToTcType, kindToTcKind, - newKindVar, tcInstSigVar, - zonkTcKindToKind, zonkTcTypeToType, zonkTcTyVars, zonkTcType, zonkTcTyVar +import TcMType ( newKindVar, zonkKindEnv, tcInstType, + checkValidType, UserTypeCtxt(..), pprUserTypeCtxt ) -import Inst ( Inst, InstOrigin(..), newMethodWithGivenTy, instToIdBndr, - instFunDeps, instFunDepsOfTheta ) -import FunDeps ( tyVarFunDep, oclose ) -import TcUnify ( unifyKind, unifyKinds, unifyTypeKind ) -import Type ( Type, PredType(..), ThetaType, UsageAnn(..), - mkTyVarTy, mkTyVarTys, mkFunTy, mkSynTy, mkUsgTy, - mkUsForAllTy, zipFunTys, hoistForAllTys, - mkSigmaTy, mkDictTy, mkPredTy, mkTyConApp, - mkAppTys, splitForAllTys, splitRhoTy, mkRhoTy, - boxedTypeKind, unboxedTypeKind, tyVarsOfType, - mkArrowKinds, getTyVar_maybe, getTyVar, - tidyOpenType, tidyOpenTypes, tidyTyVar, tidyTyVars, - tyVarsOfType, tyVarsOfTypes, mkForAllTys +import TcUnify ( unifyKind, unifyOpenTypeKind ) +import TcType ( Type, Kind, SourceType(..), ThetaType, TyVarDetails(..), + TcTyVar, TcKind, TcThetaType, TcTauType, + mkTyVarTy, mkTyVarTys, mkFunTy, + hoistForAllTys, zipFunTys, + mkSigmaTy, mkPredTy, mkGenTyConApp, mkTyConApp, mkAppTys, + liftedTypeKind, unliftedTypeKind, mkArrowKind, + mkArrowKinds, tcSplitFunTy_maybe ) -import PprType ( pprConstraint, pprType ) -import Subst ( mkTopTyVarSubst, substTy ) -import Id ( mkVanillaId, idName, idType, idFreeTyVars ) -import Var ( TyVar, mkTyVar, mkNamedUVar, varName ) -import VarEnv -import VarSet -import Bag ( bagToList ) +import Inst ( Inst, InstOrigin(..), newMethodWithGivenTy, instToId ) + +import Id ( mkLocalId, idName, idType ) +import Var ( TyVar, mkTyVar, tyVarKind ) import ErrUtils ( Message ) -import TyCon ( TyCon ) -import Name ( Name, OccName, isLocallyDefined ) -import TysWiredIn ( mkListTy, mkTupleTy ) -import UniqFM ( elemUFM, foldUFM ) +import TyCon ( TyCon, tyConKind ) +import Class ( classTyCon ) +import Name ( Name ) +import NameSet +import TysWiredIn ( mkListTy, mkPArrTy, mkTupleTy, genUnitTyCon ) import BasicTypes ( Boxity(..) ) import SrcLoc ( SrcLoc ) -import Unique ( Unique, Uniquable(..) ) -import Util ( mapAccumL, isSingleton, removeDups ) +import Util ( lengthIs ) import Outputable + \end{code} @@ -68,253 +64,467 @@ import Outputable %* * %************************************************************************ -tcHsType and tcHsTypeKind -~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +Generally speaking we now type-check types in three phases + + 1. Kind check the HsType [kcHsType] + 2. Convert from HsType to Type, and hoist the foralls [tcHsType] + 3. Check the validity of the resulting type [checkValidType] + +Often these steps are done one after the othe (tcHsSigType). +But in mutually recursive groups of type and class decls we do + 1 kind-check the whole group + 2 build TyCons/Classes in a knot-tied wa + 3 check the validity of types in the now-unknotted TyCons/Classes + +\begin{code} +tcHsSigType :: UserTypeCtxt -> RenamedHsType -> TcM Type + -- Do kind checking, and hoist for-alls to the top +tcHsSigType ctxt ty = tcAddErrCtxt (checkTypeCtxt ctxt ty) ( + kcTypeType ty `thenTc_` + tcHsType ty + ) `thenTc` \ ty' -> + checkValidType ctxt ty' `thenTc_` + returnTc ty' + +checkTypeCtxt ctxt ty + = vcat [ptext SLIT("In the type:") <+> ppr ty, + ptext SLIT("While checking") <+> pprUserTypeCtxt ctxt ] + +tcHsType :: RenamedHsType -> TcM Type + -- Don't do kind checking, nor validity checking, + -- but do hoist for-alls to the top + -- This is used in type and class decls, where kinding is + -- done in advance, and validity checking is done later + -- [Validity checking done later because of knot-tying issues.] +tcHsType ty = tc_type ty `thenTc` \ ty' -> + returnTc (hoistForAllTys ty') + +tcHsTheta :: RenamedContext -> TcM ThetaType +-- Used when we are expecting a ClassContext (i.e. no implicit params) +-- Does not do validity checking, like tcHsType +tcHsTheta hs_theta = mapTc tc_pred hs_theta + +-- 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 ty +\end{code} + + +%************************************************************************ +%* * +\subsection{Kind checking} +%* * +%************************************************************************ -tcHsType checks that the type really is of kind Type! +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} -kcHsType :: RenamedHsType -> TcM c () - -- Kind-check the type -kcHsType ty = tc_type ty `thenTc_` - returnTc () - -tcHsSigType :: RenamedHsType -> TcM s TcType - -- Used for type sigs written by the programmer - -- Hoist any inner for-alls to the top -tcHsSigType ty - = tcHsType ty `thenTc` \ ty' -> - returnTc (hoistForAllTys ty') - -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. +-- tcHsTyVars is used for type variables in type signatures +-- e.g. forall a. a->a +-- They are immutable, because they scope only over the signature +-- They may or may not be explicitly-kinded +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) + + + +tcAddScopedTyVars :: [RenamedHsType] -> TcM a -> TcM a +-- tcAddScopedTyVars is used for scoped type variables +-- added by pattern type signatures +-- e.g. \ (x::a) (y::a) -> x+y +-- They never have explicit kinds (because this is source-code only) +-- They are mutable (because they can get bound to a more specific type) + +-- Find the not-already-in-scope signature type variables, +-- kind-check them, and bring them into scope -- --- 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') `thenTc` \ ty'' -> - returnTc (hoistForAllTys ty'') - -tcHsTopBoxedType :: RenamedHsType -> TcM s Type -tcHsTopBoxedType ty - = -- tcAddErrCtxt (typeCtxt ty) $ - tc_boxed_type ty `thenTc` \ ty' -> - forkNF_Tc (zonkTcTypeToType ty') `thenTc` \ ty'' -> - returnTc (hoistForAllTys ty'') - -tcHsTopTypeKind :: RenamedHsType -> TcM s (TcKind, Type) -tcHsTopTypeKind ty - = -- tcAddErrCtxt (typeCtxt ty) $ - tc_type_kind ty `thenTc` \ (kind, ty') -> - forkNF_Tc (zonkTcTypeToType ty') `thenTc` \ zonked_ty -> - returnNF_Tc (kind, hoistForAllTys zonked_ty) +-- We no longer specify that these type variables must be univerally +-- quantified (lots of email on the subject). If you want to put that +-- back in, you need to +-- a) Do a checkSigTyVars after thing_inside +-- b) More insidiously, don't pass in expected_ty, else +-- we unify with it too early and checkSigTyVars barfs +-- Instead you have to pass in a fresh ty var, and unify +-- it with expected_ty afterwards +tcAddScopedTyVars [] thing_inside + = thing_inside -- Quick get-out for the empty case + +tcAddScopedTyVars sig_tys thing_inside + = tcGetEnv `thenNF_Tc` \ env -> + let + all_sig_tvs = foldr (unionNameSets . extractHsTyVars) emptyNameSet sig_tys + sig_tvs = filter not_in_scope (nameSetToList all_sig_tvs) + not_in_scope tv = not (tcInLocalScope env tv) + in + mapNF_Tc newNamedKindVar sig_tvs `thenTc` \ kind_env -> + tcExtendKindEnv kind_env (kcHsSigTypes sig_tys) `thenTc_` + zonkKindEnv kind_env `thenNF_Tc` \ tvs_w_kinds -> + listTc [ tcNewMutTyVar name kind PatSigTv + | (name, kind) <- tvs_w_kinds] `thenNF_Tc` \ tyvars -> + tcExtendTyVarEnv tyvars thing_inside +\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 +kcHsSigTypes tys = mapTc_ kcHsSigType tys +kcHsLiftedSigType = kcLiftedType + +--------------------------- +kcHsType :: RenamedHsType -> TcM TcKind +kcHsType (HsTyVar name) = kcTyVar name + +kcHsType (HsKindSig ty k) + = kcHsType ty `thenTc` \ k' -> + unifyKind k k' `thenTc_` + returnTc k + +kcHsType (HsListTy ty) + = kcLiftedType ty `thenTc` \ tau_ty -> + returnTc liftedTypeKind + +kcHsType (HsPArrTy 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 (HsOpTy ty1 HsArrow ty2) + = kcTypeType ty1 `thenTc_` + kcTypeType ty2 `thenTc_` + returnTc liftedTypeKind + +kcHsType ty@(HsOpTy ty1 (HsTyOp 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 (HsParTy ty) -- Skip parentheses markers + = kcHsType ty + +kcHsType (HsNumTy _) -- The unit type for generics + = returnTc liftedTypeKind + +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 tcSplitFunTy_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 + + +--------------------------- +kc_pred :: RenamedHsPred -> TcM TcKind -- Does *not* check for a saturated + -- application (reason: used from TcDeriv) +kc_pred pred@(HsIParam name ty) + = kcHsType ty + +kc_pred pred@(HsClassP cls tys) + = kcClass cls `thenTc` \ kind -> + mapTc kcHsType tys `thenTc` \ arg_kinds -> + newKindVar `thenNF_Tc` \ kv -> + unifyKind kind (mkArrowKinds arg_kinds kv) `thenTc_` + returnTc kv + +--------------------------- +kcHsContext ctxt = mapTc_ kcHsPred ctxt + +kcHsPred pred -- Checks that the result is of kind liftedType + = tcAddErrCtxt (appKindCtxt (ppr pred)) $ + kc_pred pred `thenTc` \ kind -> + unifyKind liftedTypeKind kind `thenTc_` + returnTc () + + + --------------------------- +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} +%************************************************************************ +%* * +\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! + +So tc_type does no validity-checking. Instead that's all done +by TcMType.checkValidType + + -------------------------- + *** END OF BIG WARNING *** + -------------------------- -The main work horse -~~~~~~~~~~~~~~~~~~~ \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@(HsTyVar name) +tc_type :: RenamedHsType -> TcM Type + +tc_type ty@(HsTyVar name) = tc_app ty [] -tc_type_kind (HsListTy ty) - = tc_boxed_type ty `thenTc` \ tau_ty -> - returnTc (boxedTypeKind, mkListTy tau_ty) +tc_type (HsKindSig ty k) + = tc_type ty -- Kind checking done already -tc_type_kind (HsTupleTy (HsTupCon _ Boxed) tys) - = mapTc tc_boxed_type tys `thenTc` \ tau_tys -> - returnTc (boxedTypeKind, mkTupleTy Boxed (length tys) tau_tys) +tc_type (HsListTy ty) + = tc_type ty `thenTc` \ tau_ty -> + returnTc (mkListTy tau_ty) -tc_type_kind (HsTupleTy (HsTupCon _ Unboxed) tys) - = mapTc tc_type tys `thenTc` \ tau_tys -> - returnTc (unboxedTypeKind, mkTupleTy Unboxed (length tys) tau_tys) +tc_type (HsPArrTy ty) + = tc_type ty `thenTc` \ tau_ty -> + returnTc (mkPArrTy tau_ty) -tc_type_kind (HsFunTy ty1 ty2) - = tc_type ty1 `thenTc` \ tau_ty1 -> - tc_type ty2 `thenTc` \ tau_ty2 -> - returnTc (boxedTypeKind, mkFunTy tau_ty1 tau_ty2) +tc_type (HsTupleTy (HsTupCon _ boxity arity) tys) + = ASSERT( tys `lengthIs` arity ) + tc_types tys `thenTc` \ tau_tys -> + returnTc (mkTupleTy boxity arity tau_tys) -tc_type_kind (HsAppTy ty1 ty2) - = tc_app ty1 [ty2] +tc_type (HsFunTy ty1 ty2) + = tc_type ty1 `thenTc` \ tau_ty1 -> + tc_type ty2 `thenTc` \ tau_ty2 -> + returnTc (mkFunTy tau_ty1 tau_ty2) -tc_type_kind (HsPredTy pred) - = tcClassAssertion True pred `thenTc` \ pred' -> - returnTc (boxedTypeKind, mkPredTy pred') +tc_type (HsOpTy ty1 HsArrow ty2) + = tc_type ty1 `thenTc` \ tau_ty1 -> + tc_type ty2 `thenTc` \ tau_ty2 -> + returnTc (mkFunTy tau_ty1 tau_ty2) -tc_type_kind (HsUsgTy usg ty) - = newUsg usg `thenTc` \ usg' -> - tc_type_kind ty `thenTc` \ (kind, tc_ty) -> - returnTc (kind, mkUsgTy usg' tc_ty) - where - newUsg usg = case usg of - HsUsOnce -> returnTc UsOnce - HsUsMany -> returnTc UsMany - HsUsVar uv_name -> tcLookupUVar uv_name `thenTc` \ uv -> - returnTc (UsVar uv) +tc_type (HsOpTy ty1 (HsTyOp op) ty2) + = tc_type ty1 `thenTc` \ tau_ty1 -> + tc_type ty2 `thenTc` \ tau_ty2 -> + tc_fun_type op [tau_ty1,tau_ty2] + +tc_type (HsParTy ty) -- Remove the parentheses markers + = tc_type ty -tc_type_kind (HsUsgForAllTy uv_name ty) +tc_type (HsNumTy n) + = ASSERT(n== 1) + returnTc (mkTyConApp genUnitTyCon []) + +tc_type (HsAppTy ty1 ty2) = tc_app ty1 [ty2] + +tc_type (HsPredTy pred) + = tc_pred pred `thenTc` \ pred' -> + returnTc (mkPredTy pred') + +tc_type full_ty@(HsForAllTy (Just tv_names) ctxt ty) = let - uv = mkNamedUVar uv_name + kind_check = kcHsContext ctxt `thenTc_` kcHsType ty in - tcExtendUVarEnv uv_name uv $ - tc_type_kind ty `thenTc` \ (kind, tc_ty) -> - returnTc (kind, mkUsForAllTy uv tc_ty) - -tc_type_kind (HsForAllTy (Just tv_names) context ty) - = tcExtendTyVarScope tv_names $ \ tyvars -> - tcContext context `thenTc` \ theta -> - tc_type_kind ty `thenTc` \ (kind, tau) -> - tcGetInScopeTyVars `thenTc` \ in_scope_vars -> - let - body_kind | null theta = kind - | otherwise = boxedTypeKind - -- 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 - check ct@(Class c tys) | ambiguous = failWithTc (ambigErr (c,tys) tau) - where ct_vars = tyVarsOfTypes tys - forall_tyvars = map varName in_scope_vars - tau_vars = tyVarsOfType tau - fds = instFunDepsOfTheta theta - tvFundep = tyVarFunDep fds - extended_tau_vars = oclose tvFundep tau_vars - ambig ct_var = (varName ct_var `elem` forall_tyvars) && - not (ct_var `elemUFM` extended_tau_vars) - ambiguous = foldUFM ((||) . ambig) False ct_vars - check _ = returnTc () - in - mapTc check theta `thenTc_` - returnTc (body_kind, mkSigmaTy tyvars theta tau) + tcHsTyVars tv_names kind_check $ \ tyvars -> + mapTc tc_pred ctxt `thenTc` \ theta -> + tc_type ty `thenTc` \ tau -> + returnTc (mkSigmaTy tyvars theta tau) + +tc_types arg_tys = mapTc tc_type arg_tys \end{code} Help functions for type applications ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ \begin{code} +tc_app :: RenamedHsType -> [RenamedHsType] -> TcM Type tc_app (HsAppTy ty1 ty2) tys = tc_app ty1 (ty2:tys) tc_app ty tys - | null tys - = tc_fun_type ty [] - - | otherwise = 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_types tys `thenTc` \ arg_tys -> + case ty of + HsTyVar fun -> tc_fun_type fun arg_tys + other -> tc_type 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 (HsTyVar name) arg_tys - = tcLookupTy name `thenTc` \ (tycon_kind, 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) - - ADataTyCon tc -> -- Data or newtype - returnTc (tycon_kind, mkTyConApp tc arg_tys) - - ASynTyCon tc 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) -> returnTc (mkGenTyConApp tc arg_tys) + + other -> failWithTc (wrongThingErr "type constructor" thing name) \end{code} Contexts ~~~~~~~~ \begin{code} +tcHsPred pred = kc_pred pred `thenTc_` tc_pred pred + -- Is happy with a partial application, e.g. (ST s) + -- Used from TcDeriv -tcContext :: RenamedContext -> TcM s ThetaType -tcContext context = mapTc (tcClassAssertion False) context - -tcClassAssertion ccall_ok assn@(HsPClass class_name tys) +tc_pred assn@(HsClassP class_name tys) = tcAddErrCtxt (appKindCtxt (ppr assn)) $ - mapAndUnzipTc tc_type_kind tys `thenTc` \ (arg_kinds, arg_tys) -> - tcLookupTy class_name `thenTc` \ (kind, thing) -> + tc_types tys `thenTc` \ arg_tys -> + tcLookupGlobal class_name `thenTc` \ thing -> case thing of - AClass clas arity -> - -- Check with kind mis-match - checkTc (arity == n_tys) err `thenTc_` - unifyKind kind (mkArrowKinds arg_kinds boxedTypeKind) `thenTc_` - returnTc (Class clas arg_tys) - where - n_tys = length tys - err = arityErr "Class" class_name arity n_tys - other -> failWithTc (tyVarAsClassErr class_name) - -tcClassAssertion ccall_ok assn@(HsPIParam name ty) + AClass clas -> returnTc (ClassP clas arg_tys) + other -> failWithTc (wrongThingErr "class" (AGlobal thing) class_name) + +tc_pred assn@(HsIParam name ty) = tcAddErrCtxt (appKindCtxt (ppr assn)) $ - tc_type_kind ty `thenTc` \ (arg_kind, arg_ty) -> + tc_type ty `thenTc` \ arg_ty -> returnTc (IParam name arg_ty) \end{code} + %************************************************************************ %* * \subsection{Type variables, with knot tying!} @@ -322,38 +532,16 @@ tcClassAssertion ccall_ok assn@(HsPIParam name ty) %************************************************************************ \begin{code} -tcExtendTopTyVarScope :: TcKind -> [HsTyVarBndr 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 :: [HsTyVarBndr 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 :: HsTyVarBndr 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 :: HsTyVarBndr 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} @@ -375,8 +563,6 @@ been instantiated. \begin{code} data TcSigInfo = TySigInfo - Name -- N, the Name in corresponding binding - TcId -- *Polymorphic* binder for this value... -- Has name = N @@ -394,28 +580,34 @@ data TcSigInfo 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 + ppr (TySigInfo id tyvars theta tau _ inst loc) = + ppr id <+> ptext SLIT("::") <+> ppr tyvars <+> ppr theta <+> ptext SLIT("=>") <+> ppr tau + +tcSigPolyId :: TcSigInfo -> TcId +tcSigPolyId (TySigInfo id _ _ _ _ _ _) = id + +tcSigMonoId :: TcSigInfo -> TcId +tcSigMonoId (TySigInfo _ _ _ _ id _ _) = id maybeSig :: [TcSigInfo] -> Name -> Maybe (TcSigInfo) -- Search for a particular signature maybeSig [] name = Nothing -maybeSig (sig@(TySigInfo sig_name _ _ _ _ _ _ _) : sigs) name - | name == sig_name = Just sig - | otherwise = maybeSig sigs name +maybeSig (sig@(TySigInfo sig_id _ _ _ _ _ _) : sigs) name + | name == idName sig_id = Just sig + | otherwise = maybeSig sigs name \end{code} \begin{code} -tcTySig :: RenamedSig -> TcM s TcSigInfo +tcTySig :: RenamedSig -> TcM TcSigInfo tcTySig (Sig v ty src_loc) - = tcAddSrcLoc src_loc $ - tcHsSigType ty `thenTc` \ sigma_tc_ty -> - mkTcSig (mkVanillaId v sigma_tc_ty) src_loc `thenNF_Tc` \ sig -> + = tcAddSrcLoc src_loc $ + tcHsSigType (FunSigCtxt v) 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 @@ -424,283 +616,27 @@ mkTcSig poly_id src_loc -- the tyvars *do* get unified with something, we want to carry on -- typechecking the rest of the program with the function bound -- to a pristine type, namely sigma_tc_ty - let - (tyvars, rho) = splitForAllTys (idType poly_id) - in - mapNF_Tc tcInstSigVar 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') = splitRhoTy rho' - -- This splitRhoTy tries hard to make sure that tau' is a type synonym - -- wherever possible, which can improve interface files. - in + tcInstType SigTv (idType poly_id) `thenNF_Tc` \ (tyvars', theta', tau') -> + newMethodWithGivenTy SignatureOrigin - poly_id - tyvar_tys' - theta' tau' `thenNF_Tc` \ inst -> + poly_id + (mkTyVarTys tyvars') + theta' tau' `thenNF_Tc` \ inst -> -- We make a Method even if it's not overloaded; no harm - instFunDeps SignatureOrigin theta' `thenNF_Tc` \ fds -> - returnNF_Tc (TySigInfo name poly_id tyvars' theta' tau' (instToIdBndr inst) (inst : fds) src_loc) - where - name = idName poly_id + returnNF_Tc (TySigInfo poly_id tyvars' theta' tau' + (instToId inst) [inst] src_loc) \end{code} %************************************************************************ %* * -\subsection{Checking signature type variables} -%* * -%************************************************************************ - -@checkSigTyVars@ is used after the type in a type signature has been unified with -the actual type found. It then checks that the type variables of the type signature -are - (a) Still all type variables - eg matching signature [a] against inferred type [(p,q)] - [then a will be unified to a non-type variable] - - (b) Still all distinct - eg matching signature [(a,b)] against inferred type [(p,p)] - [then a and b will be unified together] - - (c) Not mentioned in the environment - eg the signature for f in this: - - g x = ... where - f :: a->[a] - f y = [x,y] - - Here, f is forced to be monorphic by the free occurence of x. - - (d) Not (unified with another type variable that is) in scope. - eg f x :: (r->r) = (\y->y) :: forall a. a->r - when checking the expression type signature, we find that - even though there is nothing in scope whose type mentions r, - nevertheless the type signature for the expression isn't right. - - Another example is in a class or instance declaration: - class C a where - op :: forall b. a -> b - op x = x - Here, b gets unified with a - -Before doing this, the substitution is applied to the signature type variable. - -We used to have the notion of a "DontBind" type variable, which would -only be bound to itself or nothing. Then points (a) and (b) were -self-checking. But it gave rise to bogus consequential error messages. -For example: - - f = (*) -- Monomorphic - - g :: Num a => a -> a - g x = f x x - -Here, we get a complaint when checking the type signature for g, -that g isn't polymorphic enough; but then we get another one when -dealing with the (Num x) context arising from f's definition; -we try to unify x with Int (to default it), but find that x has already -been unified with the DontBind variable "a" from g's signature. -This is really a problem with side-effecting unification; we'd like to -undo g's effects when its type signature fails, but unification is done -by side effect, so we can't (easily). - -So we revert to ordinary type variables for signatures, and try to -give a helpful message in checkSigTyVars. - -\begin{code} -checkSigTyVars :: [TcTyVar] -- Universally-quantified type variables in the signature - -> TcTyVarSet -- Tyvars that are free in the type signature - -- These should *already* be in the global-var set, and are - -- used here only to improve the error message - -> TcM s [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) - (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 -> - zonkTcTyVars in_scope_tvs `thenNF_Tc` \ in_scope_tys -> - let - in_scope_assoc = [ (zonked_tv, in_scope_tv) - | (z_ty, in_scope_tv) <- in_scope_tys `zip` in_scope_tvs, - Just zonked_tv <- [getTyVar_maybe z_ty] - ] - in_scope_env = mkVarEnv in_scope_assoc - in - - -- "check" checks each sig tyvar in turn - foldlNF_Tc check - (env2, in_scope_env, []) - (tidy_tvs `zip` tidy_tys) `thenNF_Tc` \ (env3, _, msgs) -> - - failWithTcM (env3, main_msg $$ nest 4 (vcat msgs)) - where - (env1, tidy_tvs) = mapAccumL tidyTyVar emptyTidyEnv sig_tyvars - (env2, tidy_tys) = tidyOpenTypes env1 sig_tys - - main_msg = ptext SLIT("Inferred type is less polymorphic than expected") - - check (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) ; - - 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) ; - - 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 [] (valueEnvIds ve) `thenNF_Tc` \ (env1, globs) -> - find_frees tv env1 [] (varSetElems free_tyvars) `thenNF_Tc` \ (env2, frees) -> - returnNF_Tc (env2, acc, escape_msg sig_tyvar tv globs frees : msgs) - - else -- All OK - returnNF_Tc (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 acc [] - = returnNF_Tc (tidy_env, acc) - -find_globals tv tidy_env acc (id:ids) - | not (isLocallyDefined id) || - 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' acc' ids - else - find_globals tv tidy_env acc ids - -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 - 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 -mk_msg tv = ptext SLIT("Quantified type variable") <+> quotes (ppr tv) -\end{code} - -These two context are used with checkSigTyVars - -\begin{code} -sigCtxt :: Message -> [TcTyVar] -> TcThetaType -> TcTauType - -> TidyEnv -> NF_TcM s (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 env1 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 (env3, msg) - -sigPatCtxt bound_tvs bound_ids tidy_env - = returnNF_Tc (env1, - sep [ptext SLIT("When checking a pattern that binds"), - nest 4 (vcat (zipWith ppr_id show_ids tidy_tys))]) - where - show_ids = filter is_interesting bound_ids - is_interesting id = any (`elemVarSet` idFreeTyVars id) bound_tvs - - (env1, tidy_tys) = tidyOpenTypes tidy_env (map idType show_ids) - ppr_id id ty = ppr id <+> dcolon <+> ppr ty - -- Don't zonk the types so we get the separate, un-unified versions -\end{code} - - -%************************************************************************ -%* * \subsection{Errors and contexts} %* * %************************************************************************ \begin{code} -typeCtxt ty = ptext SLIT("In the type") <+> quotes (ppr ty) - typeKindCtxt :: RenamedHsType -> Message typeKindCtxt ty = sep [ptext SLIT("When checking that"), nest 2 (quotes (ppr ty)), @@ -709,17 +645,13 @@ 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 - -tyVarAsClassErr name - = ptext SLIT("Type variable used as a class:") <+> ppr name - -ambigErr (c, ts) ty - = sep [ptext SLIT("Ambiguous constraint") <+> quotes (pprConstraint c ts), - nest 4 (ptext SLIT("for the type:") <+> ppr ty), - nest 4 (ptext SLIT("Each forall'd type variable mentioned by the constraint must appear after the =>"))] +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") \end{code}