Haskell运算符“<>”的含义是什么？ [英] What is the meaning of the Haskell operator "<>"?

问题描述

在Haskell中，<>< $ code>运算符的含义是什么（与<>< /& c>或< $> ）。在研究 optparse-applicative包时，我看到了它的参考资料。 Google和LYAH似乎都没有任何信息。

haskell.org/package/base-4.9.0.0/docs/Data-Monoid.html#v:mappendrel =noreferrer> mappend ，from Data.Monoid

 （<>）:: Monoid m => m  - > m  - > m 
（<>）= mappend 
  

mappend 一起打破两个monoidal值。例如，使用list monoid，

  ghci> [1,2,3]<> [4,5,6] 
 [1,2,3,4,5,6] 
  

当您看到一个您无法识别的功能时，您通常可以在API搜索引擎上找到它，例如 Hoogle 或 Hayoo 。

In Haskell, what is the meaning of the <> operator (as distinct from <*> or <$>). I am seeing references to it while researching the optparse-applicative package. Neither Google nor LYAH seem to have any information.

解决方案

It's an alias for mappend, from the Data.Monoid module.

(<>) :: Monoid m => m -> m -> m
(<>) = mappend

mappend smashes two monoidal values together. For example, using the list monoid,

ghci> [1,2,3] <> [4,5,6]
[1,2,3,4,5,6]

When you see a function you don't recognise, you can often find it on API search engines like Hoogle or Hayoo.

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