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CGenie/rankntype.hs

Created February 11, 2015 19:20
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RankNType question
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rankntype.hs
{-# LANGUAGE RankNTypes #-}
module Main
where
class Zeroable a where
zero :: a -> Int
data Thing = Thing { x :: Int }
instance Zeroable Thing where
zero thing = 0
data System = System {
things :: (Zeroable a) => [a]
}
mapper :: System -> [Int]
mapper system = map zero (things system)
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