factor out duplicated lines that work with CPP

Author: damhiya

src/DFAMin.hs

@@ -163,21 +163,16 @@ groupEquivStates DFA { dfa_states = statemap }
     go r (a:q) = uncurry go $ List.foldl' go0 (a:r,q) xs
       where
         xs :: [EquivalenceClass]
-#if MIN_VERSION_containers(0, 6, 0)
         xs =
           [ x
           | preimageMap <- IM.elems bigmap
+#if MIN_VERSION_containers(0, 6, 0)
           , let x = IS.unions (IM.restrictKeys preimageMap a)
-          , not (IS.null x)
-          ]
 #else
-        xs =
-          [ x
-          | preimageMap <- IM.elems bigmap
           , let x = IS.unions [IM.findWithDefault IS.empty s preimageMap | s <- IS.toList a]
+#endif
           , not (IS.null x)
           ]
-#endif
 
         refineWith
           :: IntSet -- preimage set that bisects the input equivalence class