Add some tests demonstrating #25.

Benchmark/RandomnessTest2.hs

@@ -0,0 +1,42 @@
+module Main where
+
+import Control.Monad
+import System.Random
+
+-- splitN :: (RandomGen g) => Int -> g -> ([g], g)
+splitN 0 g = ([], g)
+splitN n g = (g1:l, g')
+  where
+  (l, g') = splitN (n-1) g2
+  (g1, g2) = split g
+
+-- The funny splitting operation.
+split' :: (RandomGen g) => g -> (g, g)
+split' g = (g12, g21)
+  where
+  (g1, g2) = split g
+  (_, g12) = split g1
+  (g21, _) = split g2
+
+-- This test checks if generators created by calling split 2 times are independent.
+-- It generates pairs of integers from 0 to n-1, using split' to
+-- generate both numbers using one seed. Then it counts how often the
+-- two numbers are equal.
+test :: (RandomGen g) => Int -> Int -> g -> Int
+test numTests n g = equals
+  where
+  (gs, _) = splitN numTests g
+  equals = count id $ map single gs
+  count p l = length $ filter p l
+  single g' = (fst $ randomR (0, n-1) g1) == (fst $ randomR (0, n-1) g2)
+    where
+    (g1, g2) = split' g'
+
+main = do
+  let g = mkStdGen 42
+  forM_ [2..15] $ \i -> do
+    let actual = test (i * 1000) i g
+    putStrLn $ "Generated " ++ show (i * 1000)
+      ++ " pairs of numbers from 0 to " ++ show (i - 1)
+      ++ " -- " ++ show actual ++ " pairs contained equal numbers "
+      ++ "and we expected about 1000."

Benchmark/RandomnessTest3.hs

@@ -0,0 +1,43 @@
+module Main where
+
+import Control.Monad
+import System.Random.TF.Gen
+import System.Random.TF.Instances
+
+splitN :: (RandomGen g) => Int -> g -> ([g], g)
+splitN 0 g = ([], g)
+splitN n g = (g1:l, g')
+  where
+  (l, g') = splitN (n-1) g2
+  (g1, g2) = split g
+
+-- The funny splitting operation.
+split' :: (RandomGen g) => g -> (g, g)
+split' g = (g12, g21)
+  where
+  (g1, g2) = split g
+  (_, g12) = split g1
+  (g21, _) = split g2
+
+-- This test checks if generators created by calling split 2 times are independent.
+-- It generates pairs of integers from 0 to n-1, using split' to
+-- generate both numbers using one seed. Then it counts how often the
+-- two numbers are equal.
+test :: (RandomGen g) => Int -> Int -> g -> Int
+test numTests n g = equals
+  where
+  (gs, _) = splitN numTests g
+  equals = count id $ map single gs
+  count p l = length $ filter p l
+  single g' = (fst $ randomR (0, n-1) g1) == (fst $ randomR (0, n-1) g2)
+    where
+    (g1, g2) = split' g'
+
+main = do
+  let g = seedTFGen (42, 42, 42, 42)
+  forM_ [2..15] $ \i -> do
+    let actual = test (i * 1000) i g
+    putStrLn $ "Generated " ++ show (i * 1000)
+      ++ " pairs of numbers from 0 to " ++ show (i - 1)
+      ++ " -- " ++ show actual ++ " pairs contained equal numbers "
+      ++ "and we expected about 1000."