X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=ghc%2Fcompiler%2Ftypecheck%2FTcMonoType.lhs;h=c5356849360e6dfc75056fc528f836b4d04600ce;hb=29e5b129c2e95d8890048f5dd27711c351db8e7e;hp=4ed8e502c0365b09e52f173cd074061e044c2d68;hpb=6c381e873e222417d9a67aeec77b9555eca7b7a8;p=ghc-hetmet.git diff --git a/ghc/compiler/typecheck/TcMonoType.lhs b/ghc/compiler/typecheck/TcMonoType.lhs index 4ed8e50..c535684 100644 --- a/ghc/compiler/typecheck/TcMonoType.lhs +++ b/ghc/compiler/typecheck/TcMonoType.lhs @@ -1,195 +1,773 @@ % -% (c) The GRASP/AQUA Project, Glasgow University, 1992-1996 +% (c) The GRASP/AQUA Project, Glasgow University, 1992-1998 % \section[TcMonoType]{Typechecking user-specified @MonoTypes@} \begin{code} -#include "HsVersions.h" - -module TcMonoType ( tcPolyType, tcMonoType, tcMonoTypeKind, tcContext ) where - -import Ubiq{-uitous-} +module TcMonoType ( tcHsType, tcHsSigType, tcHsTypeKind, tcHsTopType, tcHsTopBoxedType, tcHsTopTypeKind, + tcContext, tcHsTyVar, kcHsTyVar, kcHsType, + tcExtendTyVarScope, tcExtendTopTyVarScope, + TcSigInfo(..), tcTySig, mkTcSig, maybeSig, + checkSigTyVars, sigCtxt, sigPatCtxt + ) where -import HsSyn ( PolyType(..), MonoType(..), Fake ) -import RnHsSyn ( RenamedPolyType(..), RenamedMonoType(..), - RenamedContext(..) - ) +#include "HsVersions.h" +import HsSyn ( HsType(..), HsTyVarBndr(..), HsUsageAnn(..), + Sig(..), HsPred(..), pprParendHsType, HsTupCon(..) ) +import RnHsSyn ( RenamedHsType, RenamedContext, RenamedSig ) +import TcHsSyn ( TcId ) import TcMonad -import TcEnv ( tcLookupTyVar, tcLookupClass, tcLookupTyCon, - tcExtendTyVarEnv, tcTyVarScope +import TcEnv ( tcExtendTyVarEnv, tcLookupTy, tcGetValueEnv, tcGetInScopeTyVars, + tcExtendUVarEnv, tcLookupUVar, + tcGetGlobalTyVars, valueEnvIds, TcTyThing(..) ) -import TcKind ( TcKind, mkTcTypeKind, mkBoxedTypeKind, - mkTcArrowKind, unifyKind, newKindVar, - kindToTcKind +import TcType ( TcType, TcKind, TcTyVar, TcThetaType, TcTauType, + typeToTcType, kindToTcKind, + newKindVar, tcInstSigVar, + zonkTcKindToKind, zonkTcTypeToType, zonkTcTyVars, zonkTcType, zonkTcTyVar ) -import ErrUtils ( arityErr ) -import Type ( GenType, Type(..), ThetaType(..), - mkTyVarTy, mkTyConTy, mkFunTy, mkAppTy, - mkSigmaTy +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, + mkArrowKinds, getTyVar_maybe, getTyVar, + tidyOpenType, tidyOpenTypes, tidyTyVar, tidyTyVars, + tyVarsOfType, tyVarsOfTypes, tyVarsOfPred, mkForAllTys ) -import TyVar ( GenTyVar, TyVar(..), mkTyVar ) -import PrelInfo ( mkListTy, mkTupleTy ) -import Type ( mkDictTy ) -import Class ( cCallishClassKeys ) -import Unique ( Unique ) -import Name ( Name(..), getNameShortName, isTyConName, getSynNameArity ) -import PprStyle -import Pretty -import Util ( zipWithEqual, panic ) +import PprType ( pprConstraint, pprType, pprPred ) +import Subst ( mkTopTyVarSubst, substTy ) +import Id ( mkVanillaId, idName, idType, idFreeTyVars ) +import Var ( TyVar, mkTyVar, mkNamedUVar, varName ) +import VarEnv +import VarSet +import Bag ( bagToList ) +import ErrUtils ( Message ) +import TyCon ( TyCon ) +import Name ( Name, OccName, isLocallyDefined ) +import TysWiredIn ( mkListTy, mkTupleTy ) +import UniqFM ( elemUFM, foldUFM ) +import BasicTypes ( Boxity(..) ) +import SrcLoc ( SrcLoc ) +import Unique ( Unique, Uniquable(..) ) +import Util ( mapAccumL, isSingleton, removeDups ) +import Outputable \end{code} -tcMonoType and tcMonoTypeKind +%************************************************************************ +%* * +\subsection{Checking types} +%* * +%************************************************************************ + +tcHsType and tcHsTypeKind ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ -tcMonoType checks that the type really is of kind Type! +tcHsType checks that the type really is of kind Type! \begin{code} -tcMonoType :: RenamedMonoType -> TcM s Type - -tcMonoType ty - = tcMonoTypeKind ty `thenTc` \ (kind,ty) -> - unifyKind kind mkTcTypeKind `thenTc_` - returnTc ty +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. +-- +-- 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) \end{code} -tcMonoTypeKind does the real work. It returns a kind and a type. + +The main work horse +~~~~~~~~~~~~~~~~~~~ \begin{code} -tcMonoTypeKind :: RenamedMonoType -> TcM s (TcKind s, Type) +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_app ty [] + +tc_type_kind (HsListTy ty) + = tc_boxed_type ty `thenTc` \ tau_ty -> + returnTc (boxedTypeKind, mkListTy tau_ty) + +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_kind (HsTupleTy (HsTupCon _ Unboxed) tys) + = mapTc tc_type tys `thenTc` \ tau_tys -> + returnTc (unboxedTypeKind, mkTupleTy Unboxed (length tys) tau_tys) + +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_kind (HsAppTy ty1 ty2) + = tc_app ty1 [ty2] + +tc_type_kind (HsPredTy pred) + = tcClassAssertion True pred `thenTc` \ pred' -> + returnTc (boxedTypeKind, mkPredTy pred') + +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_kind (HsUsgForAllTy uv_name ty) + = let + uv = mkNamedUVar uv_name + in + tcExtendUVarEnv uv_name uv $ + tc_type_kind ty `thenTc` \ (kind, tc_ty) -> + returnTc (kind, mkUsForAllTy uv tc_ty) + +tc_type_kind full_ty@(HsForAllTy (Just tv_names) context ty) + = tcExtendTyVarScope tv_names $ \ forall_tyvars -> + tcContext context `thenTc` \ theta -> + tc_type_kind ty `thenTc` \ (kind, tau) -> + 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 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. + + tau_vars = tyVarsOfType tau + fds = instFunDepsOfTheta theta + tvFundep = tyVarFunDep fds + extended_tau_vars = oclose tvFundep tau_vars + is_ambig ct_var = (ct_var `elem` forall_tyvars) && + not (ct_var `elemUFM` extended_tau_vars) + is_free ct_var = not (ct_var `elem` forall_tyvars) + + check_pred pred = checkTc (not any_ambig) (ambigErr pred full_ty) `thenTc_` + checkTc (not all_free) (freeErr pred full_ty) + where + ct_vars = varSetElems (tyVarsOfPred pred) + any_ambig = is_source_polytype && any is_ambig ct_vars + all_free = all is_free ct_vars + + -- 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). + is_source_polytype = case tv_names of + (UserTyVar _ : _) -> True + other -> False + in + mapTc check_pred theta `thenTc_` + returnTc (body_kind, mkSigmaTy forall_tyvars theta tau) +\end{code} -tcMonoTypeKind (MonoTyVar name) - = tcLookupTyVar name `thenNF_Tc` \ (kind,tyvar) -> - returnTc (kind, mkTyVarTy tyvar) - +Help functions for type applications +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ -tcMonoTypeKind (MonoListTy ty) - = tcMonoType ty `thenTc` \ tau_ty -> - returnTc (mkTcTypeKind, mkListTy tau_ty) +\begin{code} +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) + where + pp_app = ppr ty <+> sep (map pprParendHsType tys) + +-- (tc_fun_type ty arg_tys) returns (kind-of ty, 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) -> + 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) +\end{code} -tcMonoTypeKind (MonoTupleTy tys) - = mapTc tcMonoType tys `thenTc` \ tau_tys -> - returnTc (mkTcTypeKind, mkTupleTy (length tys) tau_tys) -tcMonoTypeKind (MonoFunTy ty1 ty2) - = tcMonoType ty1 `thenTc` \ tau_ty1 -> - tcMonoType ty2 `thenTc` \ tau_ty2 -> - returnTc (mkTcTypeKind, mkFunTy tau_ty1 tau_ty2) +Contexts +~~~~~~~~ +\begin{code} -tcMonoTypeKind (MonoTyApp name tys) - = mapAndUnzipTc tcMonoTypeKind tys `thenTc` \ (arg_kinds, arg_tys) -> +tcContext :: RenamedContext -> TcM s ThetaType +tcContext context = mapTc (tcClassAssertion False) context + +tcClassAssertion ccall_ok assn@(HsPClass class_name tys) + = tcAddErrCtxt (appKindCtxt (ppr assn)) $ + mapAndUnzipTc tc_type_kind tys `thenTc` \ (arg_kinds, arg_tys) -> + tcLookupTy class_name `thenTc` \ (kind, 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) + = tcAddErrCtxt (appKindCtxt (ppr assn)) $ + tc_type_kind ty `thenTc` \ (arg_kind, arg_ty) -> + returnTc (IParam name arg_ty) +\end{code} - tc_mono_name name `thenNF_Tc` \ (fun_kind, fun_ty) -> - newKindVar `thenNF_Tc` \ result_kind -> - unifyKind fun_kind (foldr mkTcArrowKind result_kind arg_kinds) `thenTc_` +%************************************************************************ +%* * +\subsection{Type variables, with knot tying!} +%* * +%************************************************************************ - -- Check for saturated application in the special case of - -- type synoyms. Here the renamer has kindly attached the - -- arity to the Name. - synArityCheck name (length tys) `thenTc_` +\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) + 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 - returnTc (result_kind, foldl mkAppTy fun_ty arg_tys) +tcHsTyVar (IfaceTyVar name kind) = returnNF_Tc (mkTyVar name (kindToTcKind kind)) --- for unfoldings only: -tcMonoTypeKind (MonoForAllTy tyvars_w_kinds ty) - = tcExtendTyVarEnv tyvar_names (tc_kinds `zip` tyvars) ( - tcMonoTypeKind ty `thenTc` \ (kind, ty') -> - unifyKind kind mkTcTypeKind `thenTc_` - returnTc (mkTcTypeKind, ty') - ) - where - (tyvar_names, kinds) = unzip tyvars_w_kinds - tyvars = zipWithEqual mk_tyvar tyvar_names kinds - tc_kinds = map kindToTcKind kinds - mk_tyvar name kind = mkTyVar (getNameShortName name) (getItsUnique name) kind - --- for unfoldings only: -tcMonoTypeKind (MonoDictTy class_name ty) - = tcMonoTypeKind ty `thenTc` \ (arg_kind, arg_ty) -> - tcLookupClass class_name `thenNF_Tc` \ (class_kind, clas) -> - unifyKind class_kind arg_kind `thenTc_` - returnTc (mkTcTypeKind, mkDictTy clas arg_ty) - - -tc_mono_name :: Name -> NF_TcM s (TcKind s, Type) -tc_mono_name name@(Short _ _) -- Must be a type variable - = tcLookupTyVar name `thenNF_Tc` \ (kind,tyvar) -> - returnNF_Tc (kind, mkTyVarTy tyvar) - -tc_mono_name name | isTyConName name -- Must be a type constructor - = tcLookupTyCon name `thenNF_Tc` \ (kind,tycon) -> - returnNF_Tc (kind, mkTyConTy tycon) - -tc_mono_name name -- Renamer should have got it right - = panic ("tc_mono_name:" ++ ppShow 1000 (ppr PprDebug name)) +kcHsTyVar :: HsTyVarBndr name -> NF_TcM s TcKind +kcHsTyVar (UserTyVar name) = newKindVar +kcHsTyVar (IfaceTyVar name kind) = returnNF_Tc (kindToTcKind kind) \end{code} -Contexts -~~~~~~~~ +%************************************************************************ +%* * +\subsection{Signatures} +%* * +%************************************************************************ + +@tcSigs@ checks the signatures for validity, and returns a list of +{\em freshly-instantiated} signatures. That is, the types are already +split up, and have fresh type variables installed. All non-type-signature +"RenamedSigs" are ignored. + +The @TcSigInfo@ contains @TcTypes@ because they are unified with +the variable's type, and after that checked to see whether they've +been instantiated. + \begin{code} +data TcSigInfo + = TySigInfo + Name -- N, the Name in corresponding binding -tcContext :: RenamedContext -> TcM s ThetaType -tcContext context = mapTc tcClassAssertion context + TcId -- *Polymorphic* binder for this value... + -- Has name = N -tcClassAssertion (class_name, tyvar_name) - = checkTc (canBeUsedInContext class_name) - (naughtyCCallContextErr class_name) `thenTc_` + [TcTyVar] -- tyvars + TcThetaType -- theta + TcTauType -- tau - tcLookupClass class_name `thenNF_Tc` \ (class_kind, clas) -> - tcLookupTyVar tyvar_name `thenNF_Tc` \ (tyvar_kind, tyvar) -> + TcId -- *Monomorphic* binder for this value + -- Does *not* have name = N + -- Has type tau - unifyKind class_kind tyvar_kind `thenTc_` + [Inst] -- Empty if theta is null, or + -- (method mono_id) otherwise - returnTc (clas, mkTyVarTy tyvar) -\end{code} + SrcLoc -- Of the signature -HACK warning: Someone discovered that @_CCallable@ and @_CReturnable@ -could be used in contexts such as: -\begin{verbatim} -foo :: _CCallable a => a -> PrimIO Int -\end{verbatim} +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 +maybeSig [] name = Nothing +maybeSig (sig@(TySigInfo sig_name _ _ _ _ _ _ _) : sigs) name + | name == sig_name = Just sig + | otherwise = maybeSig sigs name +\end{code} -Doing this utterly wrecks the whole point of introducing these -classes so we specifically check that this isn't being done. \begin{code} -canBeUsedInContext :: Name -> Bool -canBeUsedInContext (ClassName uniq _ _) = not (uniq `elem` cCallishClassKeys) -canBeUsedInContext other = True +tcTySig :: RenamedSig -> TcM s TcSigInfo + +tcTySig (Sig v ty src_loc) + = tcAddSrcLoc src_loc $ + tcAddErrCtxt (tcsigCtxt v) $ + tcHsSigType ty `thenTc` \ sigma_tc_ty -> + mkTcSig (mkVanillaId v sigma_tc_ty) src_loc `thenNF_Tc` \ sig -> + returnTc sig + +mkTcSig :: TcId -> SrcLoc -> NF_TcM s TcSigInfo +mkTcSig poly_id src_loc + = -- Instantiate this type + -- It's important to do this even though in the error-free case + -- we could just split the sigma_tc_ty (since the tyvars don't + -- unified with anything). But in the case of an error, when + -- 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 + newMethodWithGivenTy SignatureOrigin + poly_id + tyvar_tys' + 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 \end{code} -Polytypes -~~~~~~~~~ + +%************************************************************************ +%* * +\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} -tcPolyType :: RenamedPolyType -> TcM s Type -tcPolyType (HsForAllTy tyvar_names context ty) - = tcTyVarScope tyvar_names (\ tyvars -> - tcContext context `thenTc` \ theta -> - tcMonoType ty `thenTc` \ tau -> - returnTc (mkSigmaTy tyvars theta tau) - ) +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} -Auxilliary functions -~~~~~~~~~~~~~~~~~~~~ +These two context are used with checkSigTyVars + \begin{code} -synArityCheck :: Name -> Int -> TcM s () -synArityCheck name n_args - = case getSynNameArity name of - Just arity | arity /= n_args -> failTc (err arity) - other -> returnTc () +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 - err arity = arityErr "Type synonym constructor" name arity n_args + 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} -Errors and contexts -~~~~~~~~~~~~~~~~~~~ + +%************************************************************************ +%* * +\subsection{Errors and contexts} +%* * +%************************************************************************ + \begin{code} -naughtyCCallContextErr clas_name sty - = ppSep [ppStr "Can't use class", ppr sty clas_name, ppStr "in a context"] +tcsigCtxt v = ptext SLIT("In a type signature for") <+> quotes (ppr v) + +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)), + ptext SLIT("is a type")] + +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 pred ty + = sep [ptext SLIT("Ambiguous constraint") <+> quotes (pprPred pred), + 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 =>"))] + +freeErr pred ty + = sep [ptext SLIT("The constraint") <+> quotes (pprPred pred) <+> + ptext SLIT("does not mention any of the universally quantified type variables"), + nest 4 (ptext SLIT("in the type") <+> quotes (ppr ty)) + ] \end{code}