點操作功能

Question

我想寫一個功能點，免費在Haskell，讓事情變得簡單可以說，我想使這個功能：

maxmin :: Ord a => a -> a -> a -> a 
maxmin a b c = max a (min b c) 

我可以改善這

maxmin a b = (max a) . (min b) 

但有什麼辦法擺脫a和b？

Answer 1

我不會說這是simplier但在這裏你去：

maxmin :: Ord a => a -> a -> a -> a            
maxmin = (. min) . (.) . max 

（從lambdabothttp://www.haskell.org/haskellwiki/Pointfree生成具有pl工具）

lambdabot> pl maxmin a b c = max a (min b c) 
maxmin = (. min) . (.) . max 

Answer 2

你只需要使用"three laws of sections"爲，

(a `op` b) = (a `op`) b = (`op` b) a = op a b 

這樣

import Control.Arrow 

maxmin a b = (max a) . (min b) 
      = (.) (max a) (min b) 
      = uncurry (.) (max a, min b) 
      = uncurry (.) . (max *** min) $ (a, b) 
      = curry (uncurry (.) . (max *** min)) a b 

它也不太可讀。 :)