-con2tag_RDR tycon = mk_tc_deriv_name tycon "con2tag_"
-tag2con_RDR tycon = mk_tc_deriv_name tycon "tag2con_"
-maxtag_RDR tycon = mk_tc_deriv_name tycon "maxtag_"
-
-mk_tc_deriv_name :: TyCon -> [Char] -> RdrName
-mk_tc_deriv_name tycon str
- = mkDerivedRdrName tc_name mk_occ
- where
- tc_name = tyConName tycon
- mk_occ tc_occ = mkVarOccFS (mkFastString new_str)
- where
- new_str = str ++ occNameString tc_occ ++ "#"
+con2tag_RDR tycon = mk_tc_deriv_name tycon mkCon2TagOcc
+tag2con_RDR tycon = mk_tc_deriv_name tycon mkTag2ConOcc
+maxtag_RDR tycon = mk_tc_deriv_name tycon mkMaxTagOcc
+
+mk_tc_deriv_name :: TyCon -> (OccName -> OccName) -> RdrName
+mk_tc_deriv_name tycon occ_fun = mkAuxBinderName (tyConName tycon) occ_fun
+
+mkAuxBinderName :: Name -> (OccName -> OccName) -> RdrName
+mkAuxBinderName parent occ_fun = mkRdrUnqual (occ_fun (nameOccName parent))
+-- Was: mkDerivedRdrName name occ_fun, which made an original name
+-- But: (a) that does not work well for standalone-deriving
+-- (b) an unqualified name is just fine, provided it can't clash with user code