How to get two values from one, point free, in Haskell?

问题

For example, given a value, v, and a function f, is there a way to get (f v,v) point free?

回答1:

Alternatively, note that for functions h and f with appropriate types,

h >>= f = \w -> f (h w) w

so you can write

f >>= (,)

回答2:

import Control.Arrow
(g &&& f) v = (g v, f v)
-- ergo,
(id &&& f) v = (v, f v)
(f &&& id) v = (f v, v)

回答3:

How about using the Applicative instance for (->)

liftA2 (,) id :: (a -> b) -> a -> (a, b)

For example

liftA2 (,) id succ 5

>>> (5,6)

来源：https://stackoverflow.com/questions/26266825/how-to-get-two-values-from-one-point-free-in-haskell