Sequence-like on tuples-CodePudding

Consider a code using a tuple:

import Data.Tuple.All  -- tuple library
import Control.Lens

..............

f2 :: (SequenceT a1 b, Each s a1 a2 b2) => s -> (a2 -> b2) -> b
f2 tpl f = sequenceT $ tpl & each %~ f

Example of the usage:

> f x = print x >> pure x
> f2 (1,2,3,4) f
1
2
3
4
(1, 2, 3, 4)

which means that as I have a map and sequence on lists, now I have f2 on tuples. But f2 depends on the tuple.

How can I write the same f2 using just lens? Without sequenceT. Is it possible?

PS. Maybe you know another similarly simple solutions?

CodePudding user response：

You indeed don't need the package tuple, only lens, since f2 is actually just flip each.

import Control.Lens

f2 :: (Each s t a b, Applicative f) => s -> (a -> f b) -> f t
f2 = flip each

main = do
  xs <- f2 (1,2,3) (\x -> print x >> pure (x :: Int))
  print xs

{- Output:
1
2
3
(1,2,3)
-}