2010/8/26 Jürgen Nicklisch-Franken
I want to generate values, so that i have some arbitrary object, which has a certain set of signals, and each set of signals has a certain set of sensor value pairs, were the values are arbitrary. However to demonstrate my problem I have an easy example, were I want to generate an instance of
data QCExample = QCExample Int Int deriving Show
and the second value should always be the double of the first. So I tried this:
instance Arbitrary QCExample where arbitrary = let i1 = arbitrary i2 = fmap (* 2) i1 in liftM2 QCExample i1 i2
You're saying that i1 is equal to the arbitrary action, not the result of such an action. As such, i2 is based upon a different arbitrary action. Consider this: instance Arbitrary QCExample where arbitrary = do i1 <- arbitrary let i2 = 2*i1 return $ QCExample i1 i2 -- Ivan Lazar Miljenovic Ivan.Miljenovic@gmail.com IvanMiljenovic.wordpress.com