如何跨多行在ghci中定义函数? [英] How to define a function in ghci across multiple lines?

问题描述

我正在尝试在 ghci 中定义任何跨越多行的简单函数，以以下为例:

I'm trying to define any simple function that spans multiple lines in ghci, take the following as an example:

let abs n | n >= 0 = n
          | otherwise = -n

到目前为止，我已经尝试在第一行之后按 Enter 键:

So far I've tried pressing Enter after the first line:

Prelude> let abs n | n >= 0 = n
Prelude>           | otherwise = -n
<interactive>:1:0: parse error on input `|'

我也尝试使用 :{ 和 :} 命令，但我没有走远:

I've also attempted to use the :{ and :} commands but I don't get far:

Prelude> :{
unknown command ':{'
use :? for help.

我在 Linux 上为 Haskell 98 使用 GHC Interactive 6.6 版，我缺少什么?

I'm using GHC Interactive version 6.6 for Haskell 98 on Linux, what am I missing?

推荐答案

对于守卫(就像你的例子)，你可以把它们都放在一行上就行了(守卫不关心间距)

For guards (like your example), you can just put them all on one line and it works (guards do not care about spacing)

let abs n | n >= 0 = n | otherwise = -n

如果你想用多个模式匹配参数的定义来编写你的函数，像这样:

If you wanted to write your function with multiple definitions that pattern match on the arguments, like this:

fact 0 = 1
fact n = n * fact (n-1)

然后你会使用大括号和分号分隔定义

Then you would use braces with semicolons separating the definitions

let { fact 0 = 1 ; fact n = n * fact (n-1) }

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