haskell - 是否有像 `>>` 这样的标准函数，但返回第一个操作数的结果？

Question

例如，假设我想读一行并按响铃:

λ getLine >> putChar '\007'
How lang and dreary is the night when I am frae my Dearie.
-- Blip and `()`. The line is lost.
λ getLine >>= (\x -> putChar '\007' >> return x
I restless lie frae e'en to morn though I were ne'er sae weary.
"I restless lie frae e'en to morn though I were ne'er sae weary."
-- A line and also a blip side effect.

这个想法似乎与 const 有很多共同点，唯一的区别是给定的值是有效的，并且都被执行，即使只保留第一个操作的值。 (与 >> 不同，它保留第二个的值。) 我的意思是这样的:

λ constM a b = a >>= \x -> b >> return x

这是一个更复杂的示例，涉及来自 Text.ParserCombinators.ReadP 的解析器:

λ readP_to_S (many1 (munch1 (not . isSpace) `constM` skipSpaces ) `constM` eof) <$> getLine
How slow ye move, ye heavy hours.
[(["How","slow","ye","move,","ye","heavy","hours."],"")]

 

我想知道这个函数在 base 中是否可用，或者可以从 base 中的其他函数轻松构造。

Answer 1

(<*) :: Applicative f => f a -> f b -> f a