[Haskell-cafe] List containing different types but all implementing the same class

[Bo Herlin]

Hi everyone. Being new to Haskell I wonder how I can make a list contain 
different types but all implementing the same class, like this:

data X = X
data Y = Y
class Z a where f :: a -> Int
instance Z X where f x = 0
instance Z Y where f y = 1
test1 :: Z a => [a]
test1 = [X,Y]
test2 = map f test1
Is it possible to make this work?
/Bo Herlin
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