Mercurial > hg > Members > atton > delta_monad
diff similar.hs @ 12:158ae705cd16
Rename Similer -> Similar
author | Yasutaka Higa <e115763@ie.u-ryukyu.ac.jp> |
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date | Tue, 02 Sep 2014 16:59:52 +0900 |
parents | similer.hs@e8a5df54480e |
children | 88d6897c391a |
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--- /dev/null Thu Jan 01 00:00:00 1970 +0000 +++ b/similar.hs Tue Sep 02 16:59:52 2014 +0900 @@ -0,0 +1,55 @@ +{-# LANGUAGE GADTs #-} + +data Similar a = (Eq a) => Similar a (a -> a) a + +instance (Eq a) => Eq (Similar a) where + s == ss = same s == same ss + +same :: (Eq a) => Similar a -> a +same (Similar x f y) = if (f x) == y then y else undefined + +mu :: (Eq a) => Similar (Similar a) -> Similar a +mu (Similar a f b) = if ((f a) == b) then b else undefined + +class EqFunctor f where + eqmap :: (Eq a, Eq b) => (a -> b) -> f a -> f b + +instance EqFunctor Similar where + eqmap f s = Similar fs id fs + where fs = f $ same s + +class EqMonad m where + (>>=) :: (Eq a, Eq b) => m a -> (a -> m b) -> m b + return ::(Eq a) => a -> m a + +instance EqMonad Similar where + return x = Similar x id x + s >>= f = mu (eqmap f s) + +similar :: (Eq a) => (a -> a) -> (a -> a) -> a -> a +similar f g x = same $ Similar x g (f x) + + + +double :: Int -> Int +double x = (2 * x) + +twicePlus :: Int -> Int +twicePlus x = x + x + +plusTwo :: Int -> Int +plusTwo x = x + 2 + +-- samples + +{- +*Main> same $ Main.return 100 Main.>>= (\x -> Similar x twicePlus $ double x) +200 + +*Main> same $ Main.return 2 Main.>>= (\x -> Similar x plusTwo $ double x) +4 + +*Main> same $ Main.return 100 Main.>>= (\x -> Similar x plusTwo $ double x) +*** Exception: Prelude.undefined +-} +