+badPatSigTvs :: TcType -> [TyVar] -> SDoc
+badPatSigTvs sig_ty bad_tvs
+ = vcat [ fsep [ptext (sLit "The type variable") <> plural bad_tvs,
+ quotes (pprWithCommas ppr bad_tvs),
+ ptext (sLit "should be bound by the pattern signature") <+> quotes (ppr sig_ty),
+ ptext (sLit "but are actually discarded by a type synonym") ]
+ , ptext (sLit "To fix this, expand the type synonym")
+ , ptext (sLit "[Note: I hope to lift this restriction in due course]") ]
+