Haskell编码风格：map，fmap或< $&gt ;? [英] Haskell coding-style: map, fmap or <$>?

问题描述

有任何理由比其他人喜欢下列符号之一，或者这只是一个偏好问题？

Is there any reason to prefer one of the following notations over the others or is this simply a matter of preference?

map toLower "FOO"

fmap toLower "FOO"

toLower <$> "FOO"

另外：我意识到< $& 与`fmap`相同。我是否正确的假设 map 只是一个较不通用的形式 fmap ？

As an aside: I realize that <$> is the same as `fmap`. Am I right in the assumption that map is just a less general form of fmap?

推荐答案

正如你所说， map code> fmap 。如果你知道你有一个列表，然后我会使用 map ，因为它使代码更清晰，如果你犯了错误的错误消息可能会更少混乱。但在很大程度上是一个偏好问题。

As you say, map is a less general form of fmap. If you know you have a list then I would use map as it makes the code clearer and if you make a mistake the error message is likely to be less confusing. However to a large extent it's a matter of preference.

（< $>） fmap 。直到GHC 7.10它没有被Prelude导出，所以在默认情况下不可用 - 但是即使使用旧的GHC版本，也很容易从 Data.Functor 或 Control.Applicative ，这些天几乎是标准的做法。

(<$>) is the same as fmap. Until GHC 7.10 it wasn't exported by the Prelude so wasn't available by default - but even with older GHC versions it's easy to import from Data.Functor or Control.Applicative and these days it's pretty much the standard way to do this.

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