moy-fp/src/Object/lens.js

A functional programming library.

import curry from '../Function/curry'

/**
 * (s -> a) -> ((a, s) -> s) -> Lens s a
 * Lens s a = Functor f => (a -> f a) -> s -> f s 
 */
const lens = curry(
  (getter, setter) => curry(
    (of, a) => of(getter(a)).map(focus => setter(focus, a))
  )
)

export default lens