Awesome
Generic random generators
![Build Status](https://github.com/Lysxia/generic-random/actions/workflows/ci.yml/badge.svg)
Generic random generators
to implement Arbitrary
instances for QuickCheck
Automating the arbitrary
boilerplate also ensures that when a type changes to
have more or fewer constructors, then the generator either fixes itself to
generate that new case (when using the uniform
distribution) or causes a
compilation error so you remember to fix it (when using an explicit
distribution).
This package also offers a simple (optional) strategy to ensure termination for
recursive types:
make Test.QuickCheck.Gen
's size parameter decrease at every recursive call;
when it reaches zero, sample directly from a trivially terminating generator
given explicitly (genericArbitraryRec
and withBaseCase
) or implicitly
(genericArbitrary'
).
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 :: IO ()
main = sample (arbitrary :: Gen (Tree ()))
Related
-
The following two packages also derive random generators, but only with a uniform distribution of constructors:
- quickcheck-arbitrary-template (TH)
- generic-arbitrary (GHC Generics)
-
testing-feat: derive enumerations for algebraic data types, which can be turned into random generators (TH).
-
boltzmann-samplers: derive Boltzmann samplers (SYB).