“@"是什么意思?符号是指参考 Haskell 中的列表吗? [英] What does the "@" symbol mean in reference to lists in Haskell?
问题描述
我遇到了一段如下所示的 Haskell 代码:
I've come across a piece of Haskell code that looks like this:
ps@(p:pt)
@ 符号在这种情况下是什么意思?我似乎在 Google 上找不到任何信息(遗憾的是很难在 Google 上搜索符号)，而且我在 Prelude 文档中找不到该函数，所以我想它一定是某种语法糖.
What does the @ symbol mean in this context? I can't seem to find any info on Google (it's unfortunately hard to search for symbols on Google), and I can't find the function in the Prelude documentation, so I imagine it must be some sort of syntactic sugar instead.
推荐答案
是的，这只是语法糖，@ 朗读为as".ps@(p:pt) 为您提供
Yes, it's just syntactic sugar, with @ read aloud as "as". ps@(p:pt) gives you names for
- 列表:
ps - 列表的头部:
p - 列表的尾部:
pt
如果没有 @，您必须在 (1) 或 (2):(3) 之间进行选择.
Without the @, you'd have to choose between (1) or (2):(3).
这个语法实际上适用于任何构造函数；如果您有 data Tree a = Tree a [Tree a]，则 t@(Tree _ kids) 可让您访问树及其子树.
This syntax actually works for any constructor; if you have data Tree a = Tree a [Tree a], then t@(Tree _ kids) gives you access to both the tree and its children.
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