diff options
Diffstat (limited to 'compiler/typecheck/TcErrors.hs')
| -rw-r--r-- | compiler/typecheck/TcErrors.hs | 20 |
1 files changed, 10 insertions, 10 deletions
diff --git a/compiler/typecheck/TcErrors.hs b/compiler/typecheck/TcErrors.hs index d56e344454..3f0f82cb1d 100644 --- a/compiler/typecheck/TcErrors.hs +++ b/compiler/typecheck/TcErrors.hs @@ -2577,15 +2577,15 @@ mk_dict_err ctxt@(CEC {cec_encl = implics}) (ct, (matches, unifiers, unsafe_over 2 (sep [ text "bound by" <+> ppr skol_info , text "at" <+> ppr (tcl_loc (implicLclEnv implic)) ]) - where ev_vars_matching = filter ev_var_matches (map evVarPred evvars) - ev_var_matches ty = case getClassPredTys_maybe ty of - Just (clas', tys') - | clas' == clas - , Just _ <- tcMatchTys tys tys' - -> True - | otherwise - -> any ev_var_matches (immSuperClasses clas' tys') - Nothing -> False + where ev_vars_matching = [ pred + | ev_var <- evvars + , let pred = evVarPred ev_var + , any can_match (pred : transSuperClasses pred) ] + can_match pred + = case getClassPredTys_maybe pred of + Just (clas', tys') -> clas' == clas + && isJust (tcMatchTys tys tys') + Nothing -> False -- Overlap error because of Safe Haskell (first -- match should be the most specific match) @@ -2716,7 +2716,7 @@ the alleged "provided" constraints, Show a. So we suppress that Implication in discardProvCtxtGivens. It's painfully ad-hoc but the truth is that adding it to the "required" -constraints would work. Suprressing it solves two problems. First, +constraints would work. Suppressing it solves two problems. First, we never tell the user that we could not deduce a "provided" constraint from the "required" context. Second, we never give a possible fix that suggests to add a "provided" constraint to the |