moy-fp/src/Functor/IO/index.js

A functional programming library.

/**
 * IO is a Functor, Monad and Applicative
 * can map
 * can join
 * can chain
 * can ap
 * always use for IO(input and output) and side effects
 * you may not need it if you are not sensitive in functional programming
 */
const IO = unsafePerformIO => Object.seal(
  Object.create(null, {
    unsafePerformIO: {
      value: unsafePerformIO,
    },
    [Symbol.toStringTag]: {
      value: 'IO',
    },
    map: {
      value: function map(fn){
        return IO(() => fn(this.unsafePerformIO()))
      },
    },
    join: {
      value: function join(){
        return this.chain(x => x)
      },
    },
    chain: {
      value: function chain(fn){
        return IO(() => fn(this.unsafePerformIO()).unsafePerformIO())
      },
    },
    ap: {
      value: function ap(I){
        return this.chain(fn => I.map(fn))
      },
    },
  })
)

/**
 * Functor IO => a -> IO a
 */
IO.of = x => IO(() => x)

export default IO