使用列表实现haskell的Map函数 [英] Map Function using list implementation haskell

问题描述

有没有办法使用list实现来编写Haskell map 函数的实现？

我保留出现错误，我认为我没有走上正轨。这是我的：

  map'::（a  - > b） - > [a]  - > [b] 
 map'_ [] = [] 
 map'xs ys = [（x，y）| x < -  xs | y<  -  ys] 
  

任何帮助或链接都能指引我走向正确的方向我相信你的意思是理解，而不是实施。我相信你的意思是理解，而不是实施。

无论哪种方式，这都是可行的：

  map'f as = [fa | a<  -  as] 
 map'（* 2）[1..5] 
  

Is there a way to write an implementation of the Haskell map function using list implementation?

I keep getting an error and I do not think I am on the right track. This is what I have:

map' :: (a -> b) -> [a] -> [b]
map' _ [] = []
map' xs ys = [ (x, y) | x <- xs | y <- ys ]

Any help or link that will guide me in the right direction would be much appreciated.

解决方案

I believe you mean "comprehension", instead of "implementation".

Either way, this would work:

map' f as = [f a | a <- as]
map' (* 2) [1..5]

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