Add `several`?

[ekmett]

import Data.Functor.Contravariant
import Data.Functor.Contravariant.Divisible

newtype Str a = Str { runStr :: Either (Either () a) (Str a, Str a) }

instance Monoid (Str a) where
  mempty      = Str (Left (Left ()))
  mappend a b = Str (Right (a,b))

unit :: a -> Str a
unit a = Str (Left (Right a))

several :: (Decidable f, Foldable g) => f a -> f (g a)
several f = contramap (foldMap unit) go where
  go = choose runStr (chosen conquer f) (divided go go)

[ekmett]

lens could also pick up

severalOf :: Decidable f => Getting (Str a) s a -> f a -> f s