+
+ -- We make a separate binding for each default method.
+ -- At one time I used a single AbsBinds for all of them, thus
+ -- AbsBind [d] [dm1, dm2, dm3] { dm1 = ...; dm2 = ...; dm3 = ... }
+ -- But that desugars into
+ -- ds = \d -> (..., ..., ...)
+ -- dm1 = \d -> case ds d of (a,b,c) -> a
+ -- And since ds is big, it doesn't get inlined, so we don't get good
+ -- default methods. Better to make separate AbsBinds for each
+
+ tc_dm sel_id_w_dm@(_, Just dm_id)
+ = tcInstTyVars tyvars `thenNF_Tc` \ (clas_tyvars, inst_tys, _) ->
+ let
+ theta = [(clas,inst_tys)]
+ in
+ newDicts origin theta `thenNF_Tc` \ (this_dict, [this_dict_id]) ->
+ let
+ avail_insts = this_dict
+ in
+ tcExtendTyVarEnvForMeths tyvars clas_tyvars (
+ tcMethodBind clas origin clas_tyvars inst_tys theta
+ default_binds [{-no prags-}] False
+ sel_id_w_dm
+ ) `thenTc` \ (defm_bind, insts_needed, (_, local_dm_id)) ->
+
+ tcAddErrCtxt (defltMethCtxt clas) $
+
+ -- tcMethodBind has checked that the class_tyvars havn't
+ -- been unified with each other or another type, but we must
+ -- still zonk them before passing them to tcSimplifyAndCheck
+ mapNF_Tc zonkTcTyVarBndr clas_tyvars `thenNF_Tc` \ clas_tyvars' ->
+
+ -- Check the context
+ tcSimplifyAndCheck
+ (ptext SLIT("class") <+> ppr clas)
+ (mkVarSet clas_tyvars')
+ avail_insts
+ insts_needed `thenTc` \ (const_lie, dict_binds) ->
+
+ let
+ full_bind = AbsBinds
+ clas_tyvars'
+ [this_dict_id]
+ [(clas_tyvars', dm_id, local_dm_id)]
+ emptyNameSet -- No inlines (yet)
+ (dict_binds `andMonoBinds` defm_bind)
+ in
+ returnTc (full_bind, const_lie)