index.js

'use strict'
const {XIterable, Root} = require('x-iterable-base')
const {iterator} = Symbol

const createYielder = (base, callback) => {
  const iterable = base.map(callback)
  return {
    [iterator]: () => iterable[iterator](),
    __proto__: base
  }
}

class RangeIterable extends XIterable(Root) {
  constructor (begin, end) {
    super()

    begin >>= 0
    end >>= 0

    return begin <= end && {

      * [iterator] () {
        for (let i = begin; i !== end; ++i) {
          yield i
        }
      },

      reverse () {
        const endMinusOne = end - 1
        return createYielder(this, value => endMinusOne - value)
      },

      __proto__: this

    }
  }

  * [iterator] () {}

  shift (delta) {
    return createYielder(this, value => value + delta)
  }

  multiply (factor) {
    return createYielder(this, value => value * factor)
  }

  static range (...args) {
    switch (args.length) {
      case 1:
        return new Range(0, args[0])
      case 2:
        return new Range(...args)
    }
    throw new RangeError('Number of provided arguments must be 1 or 2')
  }
}

class Range extends RangeIterable {}
module.exports = Range