Hello Haskell Café,

A new version of LeanCheck is out (v0.9.0). LeanCheck is a property testing library (like QuickCheck) that tests values enumeratively.

Example. Here’s 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 for more details.

Whats new? Version 0.9.0 marks the addition of Listable typeclass instances for most standard Haskell types defined in the Haskell 2010 Language Report. This means you’ll be able to test more functions without needing to define Listable instances yourself. LeanCheck’s changelog provides more details.

A separate package [leancheck-instances] provides instances for other types in the Haskell Platform.

Installing. You can find LeanCheck on Hackage or GitHub. It is also tracked on Stackage. As usual, you can install it with:

    $ cabal install leancheck

– Rudy

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