Derive simple random generators for QuickCheck using generics.
Example
{-# LANGUAGE DeriveGeneric #-}
import GHC.Generics (Generic)
import Test.QuickCheck
import Generic.Random
data Tree a = Leaf | Node (Tree a) a (Tree a)
deriving (Show, Generic)
instance Arbitrary a => Arbitrary (Tree a) where
arbitrary = genericArbitraryRec uniform `withBaseCase` return Leaf
-- Equivalent to
-- > arbitrary =
-- > sized $ \n ->
-- > if n == 0 then
-- > return Leaf
-- > else
-- > oneof
-- > [ return Leaf
-- > , resize (n `div` 3) $
-- > Node <$> arbitrary <*> arbitrary <*> arbitrary
-- > ]
main = sample (arbitrary :: Gen (Tree ()))
Features
User-specified distribution of constructors.
A simple (optional) strategy to ensure termination for recursive types:
using genericArbitrary', Test.QuickCheck.Gen’s size parameter decreases
at every recursive call; when it reaches zero, sample directly from a
trivially terminating generator.