https://github.com/lysxia/generic-random
Generic random generators
https://github.com/lysxia/generic-random
arbitrary generics haskell quickcheck random-generation testing
Last synced: 6 months ago
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Generic random generators
- Host: GitHub
- URL: https://github.com/lysxia/generic-random
- Owner: Lysxia
- License: mit
- Created: 2016-04-06T21:37:34.000Z (almost 10 years ago)
- Default Branch: master
- Last Pushed: 2023-03-14T01:05:58.000Z (almost 3 years ago)
- Last Synced: 2025-07-13T01:37:48.699Z (6 months ago)
- Topics: arbitrary, generics, haskell, quickcheck, random-generation, testing
- Language: Haskell
- Size: 285 KB
- Stars: 81
- Watchers: 7
- Forks: 6
- Open Issues: 6
-
Metadata Files:
- Readme: README.md
- Changelog: CHANGELOG.md
- License: LICENSE
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README
Generic random generators [](https://hackage.haskell.org/package/generic-random) [](https://github.com/Lysxia/generic-random/actions/workflows/ci.yml)
=========================
Generic random generators
to implement `Arbitrary` instances for [QuickCheck](https://hackage.haskell.org/package/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
-------
```haskell
{-# 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](https://hackage.haskell.org/package/quickcheck-arbitrary-template) (TH)
+ [generic-arbitrary](https://hackage.haskell.org/package/generic-arbitrary-0.1.0) (GHC Generics)
- [testing-feat](http://hackage.haskell.org/package/testing-feat):
derive enumerations for algebraic data types, which can be turned into random generators (TH).
- [boltzmann-samplers](https://hackage.haskell.org/package/boltzmann-samplers):
derive Boltzmann samplers (SYB).