Prove termination of diff algorithm implementation

bench/bench.hs

@@ -24,7 +24,10 @@ doBenchMarks seed =
   let rbools = randoms (mkStdGen seed) :: [Bool]
       (s1000_1, rbools1) = splitAt 1000 rbools
       (s1000_2, rbools2) = splitAt 1000 rbools1
-  in s1000_1 `deepseq` s1000_2 `deepseq` defaultMain [
-    bgroup "diff bool lists" $ [bench "1000 bools" $ nf (getDiff s1000_1) s1000_2]
-    ]
-
+      s500_2 = take 500 s1000_2
+  in (s1000_1, s1000_2, s500_2) `deepseq` defaultMain
+      [ bgroup "diff bool lists"
+          [ bench "1000 bools" $ nf (getDiff s1000_1) s1000_2
+          , bench "1000/500 bools" $ nf (getDiff s1000_1) s500_2
+          ]
+      ]