Add intial implementation of SeedGen

CHANGELOG.md

@@ -1,5 +1,7 @@
 # 1.3.0
 
+* Add `Seed`, `SeedGen`, `seedSize`, `mkSeed` and `unSeed`:
+  [#162](https://github.com/haskell/random/pull/162)
 * Add `SplitGen` and `splitGen`: [#160](https://github.com/haskell/random/pull/160)
 * Add `shuffleList` and `shuffleListM`: [#140](https://github.com/haskell/random/pull/140)
 * Add `mkStdGen64`: [#155](https://github.com/haskell/random/pull/155)

bench-legacy/SimpleRNGBench.hs

@@ -1,8 +1,13 @@
-{-# LANGUAGE BangPatterns, ScopedTypeVariables, ForeignFunctionInterface #-}
+{-# LANGUAGE BangPatterns #-}
+{-# LANGUAGE DataKinds #-}
+{-# LANGUAGE ForeignFunctionInterface #-}
+{-# LANGUAGE GeneralizedNewtypeDeriving #-}
+{-# LANGUAGE ScopedTypeVariables #-}
+{-# LANGUAGE TypeFamilies #-}
+{-# LANGUAGE UndecidableInstances #-}
 {-# OPTIONS_GHC -fwarn-unused-imports #-}
 
 -- | A simple script to do some very basic timing of the RNGs.
-
 module Main where
 
 import System.Exit (exitSuccess, exitFailure)
@@ -80,13 +85,18 @@ measureFreq = do
 
 -- Test overheads without actually generating any random numbers:
 data NoopRNG = NoopRNG
+instance SeedGen NoopRNG where
+  type SeedSize NoopRNG = 1
+  seedGen = error "NoopRNG"
+  unseedGen = error "NoopRNG"
 instance RandomGen NoopRNG where
   next g = (0, g)
   genRange _ = (0, 0)
   split g = (g, g)
 
 -- An RNG generating only 0 or 1:
-data BinRNG = BinRNG StdGen
+newtype BinRNG = BinRNG StdGen
+  deriving (SeedGen)
 instance RandomGen BinRNG where
   next (BinRNG g) = (x `mod` 2, BinRNG g')
     where

src/System/Random.hs

@@ -30,6 +30,11 @@ module System.Random
       , genWord64R
       , unsafeUniformFillMutableByteArray
       )
+  , SeedGen (..)
+  , Seed
+  , mkSeed
+  , unSeed
+  , seedSize
   , SplitGen (splitGen)
   , uniform
   , uniformR