moy-fp/src/Object/set.js

A functional programming library.

import curry from '../Function/curry'

// simple internal Functor Identity
// you can also use external Identity to implement set, but it const more performance
const Identity = a => ({
  value: a,
  map(f){
    return Identity(f(this.value))
  },
})

// here we just use .value, and not use extract or Comonad, assue it has no side effects

/**
 * Lens s a -> a -> s -> s
 * Lens s a = Functor f => (a -> f a) -> s -> f s 
 */
const set = curry(
  (Lens, v, a) => Lens(() => Identity(v))(a).value
)

export default set