``hello''++``world''在Haskell中不起作用 [英] ''hello'' ++ ''world'' doesn't work in Haskell

问题描述

只想澄清一下这是我的第一天编程，所以我意识到这个问题是多么愚蠢:D

Just want to clarify that it's my first day programming, and I realise how dumb this question is :D

1)为什么不起作用?

1) Why doesn't it work?

ghci>''hello'' ++ ''world''

<interactive>:40:1: error
    * Syntax error on ''hello''
      Perhaps you intended to use TemplateHaskell or TemplateHaskellQuotes
    * In the Template Haskell quotation ''hello''

ghci>''hello'' ++ '' '' ++ ''world''

<interactive>:41:17: error: parse error on input '''

我应该在文本编辑器中添加一些东西使其工作吗?还是我只是犯了一些菜鸟错误?

Should I add something in the texteditor to make it work? Or did I just do some rookie mistake?

2)

ghci> ''Steve'' !! 2

<interactive>:42:2: error
    * Syntax error on ''Steve''
      Perhaps you intended to use TemplateHaskell or TemplateHaskellQuotes
    * In the Template Haskell quotation ''Steve''
ghci>[1,2,3,5,8] !! 2
3

当我用数字执行这些命令时，它可以工作，但不能用字符.我一定做错了，但是我不确定:/

When I do these commands with numbers it works, but not with characters. I must be doing something wrong, but I'm not sure what :/

提前谢谢！

推荐答案

字符串用双引号包围(例如".." )，而不是两个单引号(如''..'').因此，您应该使用"而不是'.

Strings are surrounded by double quotes (like ".."), not two single quotes (as in ''..''). You thus should use " instead of '.

例如:

$ ghci
GHCi, version 8.0.2: http://www.haskell.org/ghc/  :? for help
Prelude> "hello" ++ "world"
"helloworld"
Prelude> "hello" ++ " " ++ "world"
"hello world"

这在 Haskell报告2010部分中针对字符和字符串文字' :

字符文字写在单引号之间，如'a'，而字符串则写在双引号之间，如"Hello" .

Character literals are written between single quotes, as in 'a', and strings between double quotes, as in "Hello".

基于这篇文章，人们可以在双引号上写上具有 Shift + '的Mac键盘，这是在标准"质询键盘上进行组织的方式:

Based on this article, one can write straight double quotes on a Mac keyboard with Shift + ', which is the way it is organized on a "standard" querty keyboard:

在任何典型的键盘上，只需按'即可获得一个连续的单个标记(')和 Shift + '表示直双标记(").

On any typical keyboard, simply press ' for a straight single mark (') and Shift + ' for a straight double mark (").

基于 @ M.Aroosi的评论，对于英国的通用键盘，"是 Shift + 2

Based on @M.Aroosi's comment, for a UK querty keyboard, the " is Shift+2

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