X-Git-Url: http://git.megacz.com/?p=ghc-hetmet.git;a=blobdiff_plain;f=compiler%2FbasicTypes%2FDataCon.lhs;fp=compiler%2FbasicTypes%2FDataCon.lhs;h=458bfd3f8193ac6eca8402344223311ed3f52898;hp=5e359848e2248b81b83eea7eeb100cb8fd7d84b5;hb=a10a21dadac041e928ad5dab3810b68ab35bc9bb;hpb=5096055e9aa46a7cc8b5a1292f7094fe588ec4d1

diff --git a/compiler/basicTypes/DataCon.lhs b/compiler/basicTypes/DataCon.lhs
index 5e359848..458bfd3 100644
--- a/compiler/basicTypes/DataCon.lhs
+++ b/compiler/basicTypes/DataCon.lhs
@@ -835,16 +835,17 @@ dataConCannotMatch :: [Type] -> DataCon -> Bool
 -- Returns True iff the data con *definitely cannot* match a 
 --		    scrutinee of type (T tys)
 --		    where T is the type constructor for the data con
---
+-- NB: look at *all* equality constraints, not only those
+--     in dataConEqSpec; see Trac #5168
 dataConCannotMatch tys con
-  | null eq_spec      = False	-- Common
+  | null theta        = False	-- Common
   | all isTyVarTy tys = False	-- Also common
   | otherwise
-  = typesCantMatch (map (substTyVar subst . fst) eq_spec)
-	           (map snd eq_spec)
+  = typesCantMatch [(Type.substTy subst ty1, Type.substTy subst ty2)
+                   | EqPred ty1 ty2 <- theta ]
   where
     dc_tvs  = dataConUnivTyVars con
-    eq_spec = dataConEqSpec con
+    theta   = dataConTheta con
     subst   = zipTopTvSubst dc_tvs tys
 \end{code}