Hello Haskell Café, A new version of LeanCheck https://hackage.haskell.org/package/leancheck is out (v1.0.0 https://hackage.haskell.org/package/leancheck). LeanCheck is a property testing library (like QuickCheck) that tests values enumeratively. *Example.* Here is a simple example of LeanCheck in action showing that sorting is idempotent and list union is not commutative:

import Test.LeanCheck import Data.List (sort, union)

check $ \xs -> sort (sort xs) == sort (xs::[Int]) +++ OK, passed 200 tests.

check $ \xs ys -> xs `union` ys == ys `union` (xs::[Int]) *** Failed! Falsifiable (after 4 tests): [] [0,0]

LeanCheck works on all types that are instances of the Listable typeclass and is able to derive instances automatically using either Template Haskell or GHC.Generics. See LeanCheck’s Haddock documentation https://hackage.haskell.org/package/leancheck/docs/Test-LeanCheck.html for more details. LeanCheck is compatible with Hspec https://hackage.haskell.org/package/hspec-leancheck, Tasty https://hackage.haskell.org/package/tasty-leancheck and test-framework https://hackage.haskell.org/package/test-framework-leancheck. *What's new?* Version 1.0.0 signalizes stability in the API. LeanCheck has not actually changed much in the past couple of years and there are no significant differences between the early 0.9 series. *Installing.* You can find LeanCheck on Hackage https://hackage.haskell.org/package/leancheck or GitHub https://github.com/rudymatela/leancheck. It is also tracked on Stackage https://www.stackage.org/package/leancheck. You can install it with: $ cabal install leancheck – Rudy