[Haskell-cafe] ANN: LeanCheck v0.9.0 -- enumerative property testing

[Brandon Allbery]

I think they're complaining about the name of the extension. Years ago, it
was a separate extension, but it got folded into ScopedTypeVariables.

On Thu, Jan 17, 2019 at 8:01 PM Rudy Matela <rudy at matela.com.br> wrote:

> On Thu, Jan 17, 2019 at 06:28:32PM +0100, Johannes Waldmann wrote:
>
> Prelude Test.LeanCheck> checkFor 1000 $ \ x y z -> isInfinite x ||
> isInfinite y || isInfinite z || (x::Double) + (y+z) == (x+y)+z *** Failed!
> Falsifiable (after 306 tests): 1.0 1.0 0.3333333333333333
>
> Turns out the enumeration in Leancheck uses Rationals, while Smallcheck
> uses encodeFloat, which happens to produce only “nice” numbers (very few
> bits set) in the beginning.
>
> I improved the LeanCheck floating enumeration starting with v0.8.0 to
> catch exactly this kind of error. :-)
>
> PS: this post wouldn’t be complete without me complaining that I cannot
> (easily) put the type annotation where it belongs - in the declaration of
> the name:
>
> Prelude Test.LeanCheck> check $ \ (x::Double) y z -> x + (y+z) == (x+y)+z
>
> :22:12: error: Illegal type signature: ‘Double’ Type signatures are only
> allowed in patterns with ScopedTypeVariables
>
> Wat? TypeVariables? There aren’t any!
>
> You can get the above to parse by passing -XScopedTypeVariables to GHC:
>
> $ ghci -XScopedTypeVariables
> > import Test.LeanCheck
> > check $ \(x::Double) y z -> x + (y+z) == (x+y) + z
> *** Failed! Falsifiable (after 87 tests):
> 0.0 Infinity (-Infinity)
>
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-- 
brandon s allbery kf8nh
allbery.b at gmail.com
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