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view similer.hs @ 9:41c71f67c103
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author | Yasutaka Higa <e115763@ie.u-ryukyu.ac.jp> |
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date | Tue, 02 Sep 2014 11:48:53 +0900 |
parents | 6e0285628ead |
children | 7c7efee7891f |
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data Similer a b = Similer a (a -> b) b instance Functor (Similer a) where fmap g (Similer a f b) = Similer a (g . f) $ g b eq :: (Eq a) => Similer a b -> Similer a b -> Bool eq (Similer a _ _ ) (Similer b _ _) = a == b eta :: a -> Similer a a eta a = Similer a id a mu :: (Eq b) => Similer a (Similer b c) -> Similer b c mu (Similer a f b) = if (eq (f a) b) then b else undefined double :: Int -> Int double x = (2 * x) twicePlus :: Int -> Int twicePlus x = x + x plusTwo :: Int -> Int plusTwo x = x + 2 same :: (Show b, Eq b) => Similer a b -> b same (Similer x f y) = if (f x) == y then y else (error ("not same :" ++ show y)) similer :: (Show b, Eq b) => (a -> b) -> (a -> b) -> a -> b similer f g x = same $ Similer x g (f x) -- samples sameExample = map (similer twicePlus double) [1..10] nonSameExample = map (similer twicePlus plusTwo) [1..10] nonSameExampleSpecific = map (similer twicePlus plusTwo) [2]