-dataConInstArgTys (MkData {dcRepArgTys = arg_tys,
- dcUnivTyVars = univ_tvs,
- dcExTyVars = ex_tvs}) inst_tys
- = ASSERT( length tyvars == length inst_tys )
+dataConInstArgTys dc@(MkData {dcRepArgTys = arg_tys,
+ dcUnivTyVars = univ_tvs,
+ dcExTyVars = ex_tvs}) inst_tys
+ = ASSERT2 ( length tyvars == length inst_tys
+ , ptext SLIT("dataConInstArgTys") <+> ppr dc $$ ppr tyvars $$ ppr inst_tys)
+