- Nothing -> returnTc Nothing -- Not source
- Just dms -> checkDefaultBinds clas op_names dms `thenTc` \ dm_env ->
+ Nothing -> -- Not source
+ returnTc Nothing
+
+ Just dms -> -- Source so do error checks
+ checkTc (gla_exts || length tyvar_names == 1)
+ (classArityErr class_name) `thenTc_`
+
+ checkDefaultBinds clas op_names dms `thenTc` \ dm_env ->