--
normaliseEqs :: [Inst] -> TcM EqConfig
normaliseEqs eqs
- = do { ASSERTM2( allM wantedEqInstIsUnsolved eqs, ppr eqs )
+ = do { WARNM2( anyM wantedEqInstIsUnsolved eqs, ppr eqs )
; traceTc $ ptext (sLit "Entering normaliseEqs")
; eqss <- mapM normEqInst eqs
msg = sep [sep [ptext (sLit "Couldn't match expected type") <+> pp_exp,
nest 7 $
ptext (sLit "against inferred type") <+> pp_act],
- nest 2 (extra_exp $$ extra_act),
- nest 2 (vcat (map pp_open_tc (nub open_tcs)))]
+ nest 2 (extra_exp $$ extra_act $$ extra_tyfun) ]
-- See Note [Non-injective type functions]
in
(env2, msg)
where
- open_tcs = [tc | TyConApp tc _ <- [ty_act, ty_exp]
- , isOpenTyCon tc ]
+ extra_tyfun
+ = case (tcSplitTyConApp_maybe ty_act, tcSplitTyConApp_maybe ty_exp) of
+ (Just (tc_act,_), Just (tc_exp,_)) | tc_act == tc_exp
+ -> if isOpenSynTyCon tc_act then pp_open_tc tc_act
+ else WARN( True, ppr tc_act) -- If there's a mis-match, then
+ empty -- it should be a family
+ _ -> empty
+
pp_open_tc tc = ptext (sLit "NB:") <+> quotes (ppr tc)
<+> ptext (sLit "is a type function") <> pp_inj
where
so pp_open_tc adds:
NB: `Depend' is type function, and hence may not be injective
-Currently we add this independently for each argument, so we also get
- Couldn't match expected type `a'
- against inferred type `Dual (Dual a)'
- NB: `Dual' is a (non-injective) type function
-which is arguably redundant. But on the other hand, it's probably
-a good idea for the programmer to know the error involves type functions
-so I've left it in for now. The obvious alternative is to only add
-this NB in the case of matching (T ...) ~ (T ...).
-
-
Warn of loopy local equalities that were dropped.
\begin{code}