问题
I found defining the following
(%) = flip fmap
I can write code like this:
readFile "/etc/passwd" % lines % filter (not . null)
To me it makes more sense than the alternative:
filter (not . null) <$> lines <$> readFile "/etc/passwd"
Obviously, it's just a matter of order.
Does anyone else do this? Is there a valid reason not to write code like this?
回答1:
Your operator (%) is exactly the operator (<&>) from the lens package.
It can be imported with:
import Control.Lens.Operators ((<&>))
回答2:
There is a similar function for the Applicative type class called <**>; it's a perfectly reasonable thing to want or use for Functor as well. Unfortunately, the semantics are a bit different for <**>, so it can't be directly widened to apply to Functor as well.
回答3:
-- (.) is to (<$>) as flip (.) is to your (%).
I usually define (&) = flip (.) and it's just like your example, you can apply function composition backwords. Allows for easier to understand points-free code in my opinion.
回答4:
Personally I wouldn't use such an operators because then I have to learn two orders in which to read programs.
来源：https://stackoverflow.com/questions/1678104/anyone-ever-flip