random-derive

This module exposes a deriveRandom function which automatically creates Random instances for data types instantiating both Enum as well as Bounded.

This is useful for getting random values (or sequences of random values) of custom types, e.g.:

{-# LANGUAGE TemplateHaskell #-}

import System.Random (mkStdGen, randoms)
import System.Random.TH

data Color = Red | Green | Blue deriving (Enum, Bounded)

$(deriveRandom ''Color)

-- Yields an infinite sequence of random colors given some initial seed.
randomColors :: Int -> [Color]
randomColors seed = randoms (mkStdGen seed)