Maybe-monad.js

export class Maybe<T> {
  value: T | null

  constructor(value: T | null) {
    this.value = value
  }

  static property<P>(value: P | undefined): Maybe<P> {
    if (value === undefined) {
      return new Maybe<P>(null)
    }

    return new Maybe<P>(value)
  }

  flatMap<M>(fn: (value: T) => Maybe<M>): Maybe<M> {
    if (this.value === null) {
      return new Maybe<M>(null)
    }

    return fn(this.value)
  }

  mapf<M>(fn: (value: T) => M): Maybe<M> {
    if (this.value === null) {
      return new Maybe<M>(null)
    }

    return new Maybe<M>(fn(this.value))
  }
}