add a simple random abstraction

Crypto/Random/Types.hs

@@ -5,13 +5,49 @@
 -- Stability   : experimental
 -- Portability : Good
 --
-{-# LANGUAGE GeneralizedNewtypeDeriving #-}
 module Crypto.Random.Types
-    ( Random(..)
+    (
+      MonadRandom(..)
+    , DRG(..)
+    , withDRG
     ) where
 
-import Data.Byteable
-import Data.SecureMem
+import Control.Applicative
+import Crypto.Random.Entropy
+import Crypto.Internal.ByteArray
 
-newtype Random = Random SecureMem
-    deriving (Eq, Byteable)
+class Monad m => MonadRandom m where
+    getRandomBytes :: ByteArray byteArray => Int -> m byteArray
+
+class DRG gen where
+    randomBytesGenerate :: ByteArray byteArray => Int -> gen -> (byteArray, gen)
+
+instance MonadRandom IO where
+    getRandomBytes = getEntropy
+
+newtype MonadPseudoRandom gen a = MonadPseudoRandom
+    { runPseudoRandom :: gen -> (a, gen)
+    }
+
+instance DRG gen => Functor (MonadPseudoRandom gen) where
+    fmap f m = MonadPseudoRandom $ \g1 ->
+        let (a, g2) = runPseudoRandom m g1 in (f a, g2)
+
+instance DRG gen => Applicative (MonadPseudoRandom gen) where
+    pure a     = MonadPseudoRandom $ \g -> (a, g)
+    (<*>) fm m = MonadPseudoRandom $ \g1 ->
+        let (f, g2) = runPseudoRandom fm g1
+            (a, g3) = runPseudoRandom m g2
+         in (f a, g3)
+
+instance DRG gen => Monad (MonadPseudoRandom gen) where
+    return a    = MonadPseudoRandom $ \g -> (a, g)
+    (>>=) m1 m2 = MonadPseudoRandom $ \g1 ->
+        let (a, g2) = runPseudoRandom m1 g1
+         in runPseudoRandom (m2 a) g2
+
+instance DRG gen => MonadRandom (MonadPseudoRandom gen) where
+    getRandomBytes n = MonadPseudoRandom (randomBytesGenerate n)
+
+withDRG :: DRG gen => gen -> MonadPseudoRandom gen a -> (a, gen)
+withDRG gen m = runPseudoRandom m gen