parser6.js

class Result {
  constructor(value, rest) {
    this.value = value
    this.rest = rest
  }
}

class Success extends Result {
  map(fn) {
    return new Success(fn(this.value), this.rest)
  }
  bimap(s, f) {
    return new Success(s(this.value), this.rest)
  }
  chain(fn) {
    return fn(this.value, this.rest)
  }
  fold(s, f) {
    return s(this.value, this.rest)
  }
}

class Failure extends Result {
  map(fn) {
    return this
  }
  bimap(s, f) {
    return new Failure(f(this.value), this.rest)
  }
  chain(fn) {
    return this
  }
  fold(s, f) {
    return f(this.value, this.rest)
  }
}