GHCi中的隐形缩进错误导致加载失败 [英] Invisible indentation error caused load failure in GHCi

问题描述

 <$ c $ 
 
我遇到了一个由棘手的缩进引起的问题，这里是  c> 1 import Data.List 
 2 myQuickSort [] = [] 
 3 myQuickSort（x：xs）= myQuickSort小++ [x] ++ myQuickSort大$ b $ 4其中small = filter （< x）xs 
 5 greater = filter（> = x）xs 
  

但是在./cat 3.hs之后，看起来，

  root @ pierr-desktop：/ opt / playGround / haskell＃cat 3.hs 
 import Data.List 
 myQuickSort [] = [] 
 myQuickSort（x：xs）= myQuickSort小++ [x] ++ myQuickSort大
 where小= （< x）xs 
 greater = filter（> = x）xs 
  

然后将其加载到ghci中。

  GHCi，版本6.8.2：http://www.haskell.org/ghc/：？寻求帮助
加载程序包基础...链接...完成。 
前奏> ：l 3.hs 
 [1的1]编译主（3.hs，解释）
 
 3.hs：5：11：解析输入错误`='
失败，模块加载：无。 
前奏> 
  

在编程haskell时，我应该如何捕捉到这个看不见的缩进错误？

编辑：
这样写，错误就会消失。这是一个推荐的方式来写在哪里绑定 - 把变量放在不同的行中？

  myQuickSort [] = [] 
 myQuickSort（x：xs）= myQuickSort小++ [x] ++ myQuickSort large 
其中
 smaller = filter（< x）xs 
 larger = filter（> = x）xs 
  

解决方案

您的问题与选项卡的扩展有关。 Haskell假设一个标签值8个空格。你的编辑可能有不同的假设。尝试搜索并用编辑器中的8个空格替换所有标签，然后调整空格以排列where子句。

I met a problem caused by the tricky Indentation, here is the code looks in VI :

  1 import Data.List
  2 myQuickSort [] = []
  3 myQuickSort (x:xs) = myQuickSort smaller ++ [x] ++ myQuickSort bigger
  4     where   smaller = filter ( < x ) xs
  5             bigger  = filter ( >=x ) xs

But after ./cat 3.hs , It looks ,

root@pierr-desktop:/opt/playGround/haskell# cat 3.hs 
import Data.List
myQuickSort [] = []
myQuickSort (x:xs) = myQuickSort smaller ++ [x] ++ myQuickSort bigger
    where   smaller = filter ( < x ) xs
                    bigger  = filter ( >=x ) xs

Then load it in ghci

GHCi, version 6.8.2: http://www.haskell.org/ghc/  :? for help
Loading package base ... linking ... done.
Prelude> :l 3.hs
[1 of 1] Compiling Main             ( 3.hs, interpreted )

3.hs:5:11: parse error on input `='
Failed, modules loaded: none.
Prelude> 

How should I catch this invisible indentation error when programming haskell?

EDIT: Write it this way , the error will go. Is it a recommendded way to write the where binding - put variables in different lines as where?

   myQuickSort [] = []
   myQuickSort (x:xs) = myQuickSort smaller ++ [x] ++ myQuickSort bigger
       where
       smaller = filter (<x) xs
       bigger =  filter (>=x) xs

解决方案

Your problem has to do with the expansion of tabs. Haskell assumes a tab is worth 8 spaces. Your editor likely has a different assumption. Try searching and replacing all tabs with 8 space in your editor, then adjust the spacing to line up the where clause.

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