underarm/lib/iterator.js

Transducers for JavaScript with Underscore API and Async extensions

'use strict'
var symIterator = require('transduce/core').protocols.iterator

module.exports = function(_r){
  _r.generate = generate

  // Transduces the current chained object by using the chained trasnformation
  // and an iterator created with the callback
  _r.prototype.generate = function(callback, callToInit){
    return this.withSource(generate(callback, callToInit))
  }

  // Creates an (duck typed) iterator that calls the provided next callback repeatedly
  // and uses the return value as the next value of the iterator.
  // Marks iterator as done if the next callback returns undefined (returns nothing)
  // Can be used to as a source obj to reduce, transduce etc
  function generate(callback, callToInit){
    var gen = {}
    gen[symIterator] = function(){
      var next = callToInit ? callback() : callback
      return {
        next: function(){
          var value = next()
          return (value === void 0) ? {done: true} : {done: false, value: value}
        }
      }
    }
    return gen
  }
}