- fixpt = mapVarEnv (substTy (mkTvSubst in_scope fixpt)) env
-
-----------------------------
-dataConCanMatch :: [Type] -> DataCon -> Bool
--- Returns True iff the data con can match a scrutinee of type (T tys)
--- where T is the type constructor for the data con
---
--- Instantiate the equations and try to unify them
-dataConCanMatch tys con
- | null eq_spec = True -- Common
- | all isTyVarTy tys = True -- Also common
- | otherwise
- = isJust (tcUnifyTys (\tv -> BindMe)
- (map (substTyVar subst . fst) eq_spec)
- (map snd eq_spec))
- where
- dc_tvs = dataConUnivTyVars con
- eq_spec = dataConEqSpec con
- subst = zipTopTvSubst dc_tvs tys
+ f e = let e' = mapUFM (substTy (mkTvSubst in_scope e)) e
+ in if and $ eltsUFM $ intersectUFM_C tcEqType e e'
+ then e
+ else f e'