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Haskell的kind by xyyiii #122

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freizl opened this Issue Apr 30, 2018 · 2 comments

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freizl commented Apr 30, 2018

data Frank a b  = Frank {frankField :: b a} 
                            deriving (Show)

大家好。我是haskell新手玩家。。。= =。看haksell 趣味指南
对于这段代码怎么理解。尤其是这个花括号是什么语法形式

@freizl freizl added the migration label Apr 30, 2018

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freizl commented Apr 30, 2018

frankField 是一个函数,类型为 Frank a b -> b a,相当于是 Frank的反函数

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freizl commented Apr 30, 2018

主要可以理解为简化如下定义

data Frank a b = Frank (b a)
                 deriving (Show)

frankField :: Frank a b => b a
frankField Frank (b a) = b a
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