查看“Haskell”的源代码

[[Category:Haskell]]
Haskell 是一种函数式编程语言。

== 笔记 ==

=== printf debugging ===

<syntaxhighlight lang=haskell>
import Debug.Trace

dbg :: Show a => String -> a -> a
dbg msg x = trace (msg ++ " " ++ show x) x
</syntaxhighlight>

使用方法：把变量 <code>x</code> 换成 {{code|haskell|2=(dbg "x =" x)}}。

=== <code>let</code> 与 <code>where</code> ===

<code>let</code> 是一个表达式，而 <code>where</code> 不是。<code>where</code> 用于给多个 guard 创建 binding，如下：
<syntaxhighlight lang=haskell>
f x y
  | y > z  = ...
  | y == z = ...
  | y < z  = ...
  where
    z = x * x
</syntaxhighlight>
三个 guard 都可使用 <code>z</code>。用 <code>let</code> 无法达到以上的效果。<ref>https://stackoverflow.com/q/4362328/10974106</ref><ref>[https://www.cse.iitb.ac.in/~as/fpcourse/haskell98_tutorial/patterns.html A Gentle Introduction to Haskell] 4.5 Lexical Scoping and Nested Forms</ref>

== Hlint ==

=== Ignore warnings ===

在 <code>.hlint.yaml</code> 中写:
<syntaxhighlight lang=yaml>
- ignore: {name: Eta reduce}
</syntaxhighlight>

<ref>https://neilmitchell.blogspot.com/2019/01/ignoring-hlint.html</ref>

== 另见 ==

* [[Functor, Applicative 和 Monad]]

== 外部链接 ==

* [https://www.haskell.org/ 主页]
* [http://cheatsheet.codeslower.com/CheatSheet.pdf Haskell CheetSheet]

== 参考资料 ==

<references />