how_to_allow = parens (ptext (sLit "Use -XFlexibleContexts to permit this"))
-check_pred_ty dflags _ pred@(EqPred ty1 ty2)
+check_pred_ty dflags ctxt pred@(EqPred ty1 ty2)
= do { -- Equational constraints are valid in all contexts if type
-- families are permitted
; checkTc (xopt Opt_TypeFamilies dflags) (eqPredTyErr pred)
+ ; checkTc (case ctxt of ClassSCCtxt {} -> False; _ -> True)
+ (eqSuperClassErr pred)
-- Check the form of the argument types
; checkValidMonoType ty1
= vcat [ptext (sLit "In the context:") <+> pprTheta theta,
ptext (sLit "While checking") <+> pprSourceTyCtxt ctxt ]
+eqSuperClassErr :: PredType -> SDoc
+eqSuperClassErr pred
+ = hang (ptext (sLit "Alas, GHC 7.0 still cannot handle equality superclasses:"))
+ 2 (ppr pred)
+
badPredTyErr, eqPredTyErr, predTyVarErr :: PredType -> SDoc
-badPredTyErr sty = ptext (sLit "Illegal constraint") <+> pprPred sty
-eqPredTyErr sty = ptext (sLit "Illegal equational constraint") <+> pprPred sty
- $$
- parens (ptext (sLit "Use -XTypeFamilies to permit this"))
+badPredTyErr pred = ptext (sLit "Illegal constraint") <+> pprPred pred
+eqPredTyErr pred = ptext (sLit "Illegal equational constraint") <+> pprPred pred
+ $$
+ parens (ptext (sLit "Use -XTypeFamilies to permit this"))
predTyVarErr pred = sep [ptext (sLit "Non type-variable argument"),
nest 2 (ptext (sLit "in the constraint:") <+> pprPred pred)]
dupPredWarn :: [[PredType]] -> SDoc