diff options
Diffstat (limited to 'compiler')
| -rw-r--r-- | compiler/typecheck/TcDeriv.lhs | 8 |
1 files changed, 7 insertions, 1 deletions
diff --git a/compiler/typecheck/TcDeriv.lhs b/compiler/typecheck/TcDeriv.lhs index 97a548d24e..fb3e7ee300 100644 --- a/compiler/typecheck/TcDeriv.lhs +++ b/compiler/typecheck/TcDeriv.lhs @@ -580,6 +580,7 @@ deriveStandalone (L loc (DerivDecl deriv_ty)) , text "cls:" <+> ppr cls , text "tys:" <+> ppr inst_tys ] -- C.f. TcInstDcls.tcLocalInstDecl1 + ; checkTc (not (null inst_tys)) derivingNullaryErr ; let cls_tys = take (length inst_tys - 1) inst_tys inst_ty = last inst_tys @@ -618,7 +619,9 @@ deriveTyData tvs tc tc_args (L loc deriv_pred) -- Given data T a b c = ... deriving( C d ), -- we want to drop type variables from T so that (C d (T a)) is well-kinded ; let cls_tyvars = classTyVars cls - kind = tyVarKind (last cls_tyvars) + ; checkTc (not (null cls_tyvars)) derivingNullaryErr + + ; let kind = tyVarKind (last cls_tyvars) (arg_kinds, _) = splitKindFunTys kind n_args_to_drop = length arg_kinds n_args_to_keep = tyConArity tc - n_args_to_drop @@ -1874,6 +1877,9 @@ genDerivStuff loc fix_env clas name tycon comaux_maybe %************************************************************************ \begin{code} +derivingNullaryErr :: MsgDoc +derivingNullaryErr = ptext (sLit "Cannot derive instances for nullary classes") + derivingKindErr :: TyCon -> Class -> [Type] -> Kind -> MsgDoc derivingKindErr tc cls cls_tys cls_kind = hang (ptext (sLit "Cannot derive well-kinded instance of form") |