[Haskell-cafe] Custom QuickCheck Gens without custom shrinks

Niklas Hambüchen mail at nh2.me
Wed Aug 15 21:35:53 CEST 2012

I wrote this Gen to generate lines of texts without \NUL and \n:

    fullLinesProp = forAll linesGen ...

    linesGen = listOf . listOf $ arbitrary `suchThat` (`notElem`
['\NUL', '\n'])
    -- alternatively:
    linesGen = arbitrary `suchThat` (all (all (`notElem` ['\NUL', '\n'])))

However, I just realized that QuickCheck disables shrinking when I use
this instead of (linesGen = arbitrary :: Gen [String]).

Why is that? Is there a way to get what I want + shrinking without
defining a custom shrink (e.g. forAllShrink)?


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