Excerpts from Jürgen Nicklisch-Franken's message of Wed Aug 25 23:32:51 -0400
2010:
> instance Arbitrary QCExample where
> arbitrary =
> let i1 = arbitrary
> i2 = fmap (* 2) i1
> in liftM2 QCExample i1 i2
What's happening here is that you are "evaluating" the random value generator
too late in the game: when you set i1 = arbitrary, no random value has been
generated yet, and i2 is thus another generator which has no relation to
what i1 might produce. You could instead do this:
arbitrary = do
i1 <- arbitrary
let i2 = i1 * 2
return (QCExample i1 i2)
Cheers,
Edward
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