diff options
Diffstat (limited to 'compiler/GHC/Tc/TyCl.hs')
| -rw-r--r-- | compiler/GHC/Tc/TyCl.hs | 40 |
1 files changed, 1 insertions, 39 deletions
diff --git a/compiler/GHC/Tc/TyCl.hs b/compiler/GHC/Tc/TyCl.hs index 98550132c5..8ff9ad0d3e 100644 --- a/compiler/GHC/Tc/TyCl.hs +++ b/compiler/GHC/Tc/TyCl.hs @@ -3058,7 +3058,7 @@ dataDeclChecks tc_name new_or_data (L _ stupid_theta) cons ----------------------------------- -consUseGadtSyntax :: [LConDecl a] -> Bool +consUseGadtSyntax :: [LConDecl GhcRn] -> Bool consUseGadtSyntax (L _ (ConDeclGADT {}) : _) = True consUseGadtSyntax _ = False -- All constructors have same shape @@ -4705,50 +4705,12 @@ noClassTyVarErr clas fam_tc badDataConTyCon :: DataCon -> Type -> SDoc badDataConTyCon data_con res_ty_tmpl - | ASSERT( all isTyVar tvs ) - tcIsForAllTy actual_res_ty - = nested_foralls_contexts_suggestion - | isJust (tcSplitPredFunTy_maybe actual_res_ty) - = nested_foralls_contexts_suggestion - | otherwise = hang (text "Data constructor" <+> quotes (ppr data_con) <+> text "returns type" <+> quotes (ppr actual_res_ty)) 2 (text "instead of an instance of its parent type" <+> quotes (ppr res_ty_tmpl)) where actual_res_ty = dataConOrigResTy data_con - -- This suggestion is useful for suggesting how to correct code like what - -- was reported in #12087: - -- - -- data F a where - -- MkF :: Ord a => Eq a => a -> F a - -- - -- Although nested foralls or contexts are allowed in function type - -- signatures, it is much more difficult to engineer GADT constructor type - -- signatures to allow something similar, so we error in the latter case. - -- Nevertheless, we can at least suggest how a user might reshuffle their - -- exotic GADT constructor type signature so that GHC will accept. - nested_foralls_contexts_suggestion = - text "GADT constructor type signature cannot contain nested" - <+> quotes forAllLit <> text "s or contexts" - $+$ hang (text "Suggestion: instead use this type signature:") - 2 (ppr (dataConName data_con) <+> dcolon <+> ppr suggested_ty) - - -- To construct a type that GHC would accept (suggested_ty), we - -- simply drag all the foralls and (=>) contexts to the front - -- of the type. - suggested_ty = mkSpecSigmaTy tvs theta rho - (tvs, theta, rho) = go (dataConUserType data_con) - - go :: Type -> ([TyVar],ThetaType,Type) - -- The returned Type has no foralls or =>, even to the right of an (->) - go ty | null arg_tys = (tvs1, theta1, rho1) - | otherwise = (tvs1 ++ tvs2, theta1 ++ theta2, mkVisFunTys arg_tys rho2) - where - (tvs1, theta1, rho1) = tcSplitNestedSigmaTys ty - (arg_tys, ty2) = tcSplitFunTys rho1 - (tvs2, theta2, rho2) = go ty2 - badGadtDecl :: Name -> SDoc badGadtDecl tc_name = vcat [ text "Illegal generalised algebraic data declaration for" <+> quotes (ppr tc_name) |