Haskell多行Lambda [英] Haskell Multi-line Lambdas

问题描述

我正在从learningyouahaskell.com学习Haskell，有这样的示例:

I am learning Haskell from learnyouahaskell.com and there is an example such that:

search :: (Eq a) => [a] -> [a] -> Bool  
search needle haystack =   
    let nlen = length needle  
    in  foldl (\acc x -
> if take nlen x == needle then True else acc) False (tails haystack) 

但是当在GHC上尝试使用此代码时，它给了我

But when tried this code with GHC, it gives me

error: parse error on input ‘-’

但是它在这种情况下起作用:

But it works when it is like this:

search :: (Eq a) => [a] -> [a] -> Bool  
search needle haystack =   
    let nlen = length needle  
    in  foldl (\acc x -> if take nlen x == needle then True else acc) False (tails haystack) 

Haskell是否具有允许多行lambda的功能，还是我缺少的东西?

Is there a feature of Haskell that allows multi-line lambdas or is that something I am missing?

推荐答案

不要破坏->

只需:

search :: (Eq a) => [a] -> [a] -> Bool  
search needle haystack =   
   let nlen = length needle  
   in  foldl (\acc x ->
if take nlen x == needle then True else acc) False (tails haystack) 

或

search :: (Eq a) => [a] -> [a] -> Bool  
search needle haystack =   
   let nlen = length needle  
   in  foldl (\acc x 
-> if take nlen x == needle then True else acc) False (tails haystack) 

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