anon.hs

{-# LANGUAGE RankNTypes #-}
{-# LANGUAGE LambdaCase #-}

import Control.Lens
import Data.Bool
import Data.Maybe

-- Control.Lens.Iso#anon
anon' ::
  a
  -> (a -> Bool)
  -> Iso' (Maybe a) a
anon' a p =
  iso
    (
      fromMaybe a
    )
    (
      \a' ->
        bool
          (Just a')
          Nothing
          (p a')
    )

anonR ::
  x
  -> (r -> Bool)
  -> Iso (Either l x) (Either x r) x r
anonR a p =
  iso
    (
      \case
        Left _ ->
          a
        Right a' ->
          a'
    )
    (
      \a' ->
        bool
          (Right a')
          (Left a)
          (p a')
    )