Haskell：用Let语句缩进 [英] Haskell : Indentation with Let Statements

问题描述

恐怕我理解了这一点，并且通常 let 块被禁止。

以下代码：

  splitWith tf xs 
 |（null xs）= [[]] 
 | （（长度xs）== 1）= [xs] 
 |否则= let tpl =（break tf xs）
x =（fst tpl）
 xrst =（snd tpl）
在[[x]中，（splitWith tf（tail xrst））] 
  

创建此语法错误：

  [1 of 1]编译Main（ch04_exercise.hs，解释）
 ch04_exercise.hs：31：26：解析错误输入'x'
  

在Sublime Text 2中摆脱了选项卡后，用于排列变量的空格。在我这样做之前，我在 x 后面的=号处得到了语法错误。

任何想法我做错了什么？ 中的必须与<$ c $

  | 在[[x]，splitWith tf（tail xrst）] 
  

$ b $中另有= let（x，xrst）= break tf xs
b


这就是为什么我通常更喜欢把 let 放在一行上的原因：

  |在[[x]，splitWith tf（tail xrst）] 
   > 
 
 
您也有不必要的括号，并且可以从一些模式匹配中获益（如上所示）。
 
I'm afraid I'm tapped out on understanding this and the let block in general.

The following code:
splitWith tf xs 
    |(null xs) = [[]]
    |((length xs) == 1) = [xs]
    |otherwise = let tpl = (break tf xs) 
                     x = (fst tpl) 
                     xrst =  (snd tpl)
         in [[x] ,(splitWith tf (tail xrst))]
Creates this syntax error:
[1 of 1] Compiling Main             ( ch04_exercise.hs, interpreted )
ch04_exercise.hs:31:26: parse error on input ‘x’
This happened after I got rid of tabs in Sublime Text 2 and put spaces in to line up the variables.  Before I did that I got the syntax error at the = sign after the x. 

Any idea what I'm doing wrong? 
解决方案
The in has to line up with the let or be on the same line:
| otherwise = let (x, xrst) = break tf xs
              in [[x], splitWith tf (tail xrst)]
Which is why I usually prefer putting let on its own line:
| otherwise =
    let (x, xrst) = break tf xs
    in [[x], splitWith tf (tail xrst)]
You also have unnecessary parentheses and could benefit from some pattern matching (as demonstrated above).

                        
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