mno2
Haskell 趣學指南

Updated 2 years ago

maoxiaoke (@maoxiaoke) started discussion #33

4 months ago · 0 comments

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注意下,Nothing 的类型为 Maybe a。它是多态的,若有函数取 Maybe Int 类型的参数,就一概可以传给它一个 Nothing,因为 Nothing 中不包含任何值。Maybe a 类型可以有 Maybe Int 的行为,正如 5 可以是 Int 也可以是 Double。与之相似,空 List 的类型是 [a],可以与一切 List 打交道。因此,我们可以 [1,2,3]++[],也可以 ["ha","ha,","ha"]++[]。

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这一段是什么意思

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