Haskell错误：解析错误输入'=' [英] Haskell Error: parse error on input `='

问题描述

规格

GHC 6.12.1

Mac OS X 10.6。 4 x64

MacBook Pro

问题

我无法使用 let 语法。以下代码拒绝编译：

  module Main其中
 
 main = let x = 1 
y = 2 
z = 3 
 in putStrLn $X =++ show x ++\\\
Y =++ show y ++\\\
Z =++ show z 
  

我试着在 y = 2 和 z = 3 甚至更多。没有骰子。

（不需要）解决方案

获得要编译的代码是

1. 用空格替换硬标签。
   
2. 替换 let 子句，其中其中子句。

赋值必须对齐，而不是 let 本身。只要分配对齐，可以使用硬标签或软标签。

正确的代码：

模块主要其中
 
 main = let 
x = 1 
y = 2 
z = 3 
 in putStrLn $ X =++ show x ++\\\
Y =++ show y ++\\\
Z =++ show z 
  

Specs

GHC 6.12.1

Mac OS X 10.6.4 x64

MacBook Pro

Problem

I'm having trouble using let syntax. The following code refuses to compile:

module Main where

main = let x = 1
        y = 2
        z = 3
    in putStrLn $ "X = " ++ show x ++ "\nY = " ++ show y ++ "\nZ = " ++ show z

I tried tabbing in y = 2 and z = 3 even more. No dice.

(Undesirable) Solutions

The only way I've gotten the code to compile is either

1. Replacing hard tabs with spaces.
2. Replacing the let clause with a where clause.

解决方案

Saizan on #haskell explains that the assignments in a let expression have to align, not let itself. As long as the assignments line up, it's okay to use hard tabs or soft tabs.

Correct code:

module Main where

main = let
        x = 1
        y = 2
        z = 3
    in putStrLn $ "X = " ++ show x ++ "\nY = " ++ show y ++ "\nZ = " ++ show z

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