Prism' as a smart constructor

Example.hs

module Example (Example, example) where

import Data.Functor (($>))
import Control.Lens (Prism', prism')
import Control.Monad (guard)

data Example
  = Example String
  deriving (Eq, Ord, Show)

example :: Prism' String Example
example =
  prism' f g
  where
    f (Example a) =
      a
    g s =
      guard (even $ length s) $> Example s