From: simonpj Date: Thu, 25 Nov 1999 10:35:48 +0000 (+0000) Subject: [project @ 1999-11-25 10:35:47 by simonpj] X-Git-Tag: Approximately_9120_patches~5490 X-Git-Url: http://git.megacz.com/?a=commitdiff_plain;h=cb5f88f09f87208fa74a424e4da7141fb5204aa2;p=ghc-hetmet.git [project @ 1999-11-25 10:35:47 by simonpj] Better error message when trying to derive classes for existentially-quantified data constructors. And a general slight tidy up in TcDeriv --- diff --git a/ghc/compiler/typecheck/Inst.lhs b/ghc/compiler/typecheck/Inst.lhs index 6d18d01..5968b1e 100644 --- a/ghc/compiler/typecheck/Inst.lhs +++ b/ghc/compiler/typecheck/Inst.lhs @@ -61,7 +61,6 @@ import Subst ( emptyInScopeSet, mkSubst, substTy, substTheta, mkTyVarSubst, mkTopTyVarSubst ) import TyCon ( TyCon ) -import Subst ( mkTyVarSubst ) import VarEnv ( lookupVarEnv, TidyEnv, lookupSubstEnv, SubstResult(..) ) diff --git a/ghc/compiler/typecheck/TcDeriv.lhs b/ghc/compiler/typecheck/TcDeriv.lhs index a689407..acc6e77 100644 --- a/ghc/compiler/typecheck/TcDeriv.lhs +++ b/ghc/compiler/typecheck/TcDeriv.lhs @@ -32,9 +32,9 @@ import Class ( classKey, Class ) import ErrUtils ( dumpIfSet, Message, pprBagOfErrors ) import MkId ( mkDictFunId ) import Id ( mkVanillaId ) -import DataCon ( dataConArgTys, isNullaryDataCon ) +import DataCon ( dataConArgTys, isNullaryDataCon, isExistentialDataCon ) import PrelInfo ( needsDataDeclCtxtClassKeys ) -import Maybes ( maybeToBool ) +import Maybes ( maybeToBool, catMaybes ) import Module ( ModuleName ) import Name ( isLocallyDefined, getSrcLoc, Name, NamedThing(..), @@ -297,8 +297,8 @@ makeDerivEqns if null local_data_tycons then returnTc [] -- Bale out now else - mapTc chk_out think_about_deriving `thenTc_` - returnTc eqns + mapTc mk_eqn derive_these `thenTc` \ maybe_eqns -> + returnTc (catMaybes maybe_eqns) where ------------------------------------------------------------------ need_deriving :: [TyCon] -> [(Class, TyCon)] @@ -310,45 +310,20 @@ makeDerivEqns tycons_to_consider ------------------------------------------------------------------ - chk_out :: (Class, TyCon) -> TcM s () - chk_out this_one@(clas, tycon) - = let - clas_key = classKey clas - - is_enumeration = isEnumerationTyCon tycon - is_single_con = maybeToBool (maybeTyConSingleCon tycon) - - single_nullary_why = SLIT("one constructor data type or type with all nullary constructors expected") - nullary_why = SLIT("data type with all nullary constructors expected") - - chk_clas clas_uniq clas_str clas_why cond - = if (clas_uniq == clas_key) - then checkTc cond (derivingThingErr clas_str clas_why tycon) - else returnTc () - in - -- Are things OK for deriving Enum (if appropriate)? - chk_clas enumClassKey (SLIT("Enum")) nullary_why is_enumeration `thenTc_` - - -- Are things OK for deriving Bounded (if appropriate)? - chk_clas boundedClassKey (SLIT("Bounded")) single_nullary_why - (is_enumeration || is_single_con) `thenTc_` - - -- Are things OK for deriving Ix (if appropriate)? - chk_clas ixClassKey (SLIT("Ix.Ix")) single_nullary_why - (is_enumeration || is_single_con) - - ------------------------------------------------------------------ cmp_deriv :: (Class, TyCon) -> (Class, TyCon) -> Ordering cmp_deriv (c1, t1) (c2, t2) = (c1 `compare` c2) `thenCmp` (t1 `compare` t2) ------------------------------------------------------------------ - mk_eqn :: (Class, TyCon) -> DerivEqn + mk_eqn :: (Class, TyCon) -> NF_TcM s (Maybe DerivEqn) -- we swizzle the tyvars and datacons out of the tycon -- to make the rest of the equation mk_eqn (clas, tycon) - = (clas, tycon, tyvars, constraints) + = case chk_out clas tycon of + Just err -> addErrTc err `thenNF_Tc_` + returnNF_Tc Nothing + Nothing -> returnNF_Tc (Just (clas, tycon, tyvars, constraints)) where clas_key = classKey clas tyvars = tyConTyVars tycon -- ToDo: Do we need new tyvars ??? @@ -371,6 +346,26 @@ makeDerivEqns ] where instd_arg_tys = dataConArgTys data_con tyvar_tys + + ------------------------------------------------------------------ + chk_out :: Class -> TyCon -> Maybe Message + chk_out clas tycon + | clas_key == enumClassKey && not is_enumeration = bog_out nullary_why + | clas_key == boundedClassKey && not is_enumeration_or_single = bog_out single_nullary_why + | clas_key == ixClassKey && not is_enumeration_or_single = bog_out single_nullary_why + | any isExistentialDataCon (tyConDataCons tycon) = Just (existentialErr clas tycon) + | otherwise = Nothing + where + clas_key = classKey clas + + is_enumeration = isEnumerationTyCon tycon + is_single_con = maybeToBool (maybeTyConSingleCon tycon) + is_enumeration_or_single = is_enumeration || is_single_con + + single_nullary_why = SLIT("one constructor data type or type with all nullary constructors expected") + nullary_why = SLIT("data type with all nullary constructors expected") + + bog_out why = Just (derivingThingErr clas tycon why) \end{code} %************************************************************************ @@ -690,12 +685,16 @@ gen_taggery_Names inst_infos \end{code} \begin{code} -derivingThingErr :: FAST_STRING -> FAST_STRING -> TyCon -> Message +derivingThingErr :: Class -> TyCon -> FAST_STRING -> Message + +derivingThingErr clas tycon why + = sep [hsep [ptext SLIT("Can't make a derived instance of"), quotes (ppr clas)], + hsep [ptext SLIT("for the type"), quotes (ppr tycon)], + parens (ptext why)] -derivingThingErr thing why tycon - = hang (hsep [ptext SLIT("Can't make a derived instance of"), ptext thing]) - 0 (hang (hsep [ptext SLIT("for the type"), quotes (ppr tycon)]) - 0 (parens (ptext why))) +existentialErr clas tycon + = sep [ptext SLIT("Can't derive any instances for type") <+> quotes (ppr tycon), + ptext SLIT("because it has existentially-quantified constructor(s)")] derivCtxt tycon = ptext SLIT("When deriving classes for") <+> quotes (ppr tycon)