angular-ui-form-validation/dist/angular-ui-form-validation.js

A plugin for performing validation in angularjs without writing lots of boilerplate code or duplicating logic.

/*
 * @name Lazy.js
 *
 * @fileOverview
 * Lazy.js is a lazy evaluation library for JavaScript.
 *
 * This has been done before. For examples see:
 *
 * - [wu.js](http://fitzgen.github.io/wu.js/)
 * - [Linq.js](http://linqjs.codeplex.com/)
 * - [from.js](https://github.com/suckgamoni/fromjs/)
 * - [IxJS](http://rx.codeplex.com/)
 * - [sloth.js](http://rfw.name/sloth.js/)
 *
 * However, at least at present, Lazy.js is faster (on average) than any of
 * those libraries. It is also more complete, with nearly all of the
 * functionality of [Underscore](http://underscorejs.org/) and
 * [Lo-Dash](http://lodash.com/).
 *
 * Finding your way around the code
 * --------------------------------
 *
 * At the heart of Lazy.js is the {@link Sequence} object. You create an initial
 * sequence using {@link Lazy}, which can accept an array, object, or string.
 * You can then "chain" together methods from this sequence, creating a new
 * sequence with each call.
 *
 * Here's an example:
 *
 *     var data = getReallyBigArray();
 *
 *     var statistics = Lazy(data)
 *       .map(transform)
 *       .filter(validate)
 *       .reduce(aggregate);
 *
 * {@link Sequence} is the foundation of other, more specific sequence types.
 *
 * An {@link ArrayLikeSequence} provides indexed access to its elements.
 *
 * An {@link ObjectLikeSequence} consists of key/value pairs.
 *
 * A {@link StringLikeSequence} is like a string (duh): actually, it is an
 * {@link ArrayLikeSequence} whose elements happen to be characters.
 *
 * An {@link AsyncSequence} is special: it iterates over its elements
 * asynchronously (so calling `each` generally begins an asynchronous loop and
 * returns immediately).
 *
 * For more information
 * --------------------
 *
 * I wrote a blog post that explains a little bit more about Lazy.js, which you
 * can read [here](http://philosopherdeveloper.com/posts/introducing-lazy-js.html).
 *
 * You can also [create an issue on GitHub](https://github.com/dtao/lazy.js/issues)
 * if you have any issues with the library. I work through them eventually.
 *
 * [@dtao](https://github.com/dtao)
 */

(function(context) {
  /**
   * Wraps an object and returns a {@link Sequence}. For `null` or `undefined`,
   * simply returns an empty sequence (see {@link Lazy.strict} for a stricter
   * implementation).
   *
   * - For **arrays**, Lazy will create a sequence comprising the elements in
   *   the array (an {@link ArrayLikeSequence}).
   * - For **objects**, Lazy will create a sequence of key/value pairs
   *   (an {@link ObjectLikeSequence}).
   * - For **strings**, Lazy will create a sequence of characters (a
   *   {@link StringLikeSequence}).
   *
   * @public
   * @param {Array|Object|string} source An array, object, or string to wrap.
   * @returns {Sequence} The wrapped lazy object.
   *
   * @exampleHelpers
   * // Utility functions to provide to all examples
   * function increment(x) { return x + 1; }
   * function isEven(x) { return x % 2 === 0; }
   * function isPositive(x) { return x > 0; }
   * function isNegative(x) { return x < 0; }
   *
   * @examples
   * Lazy([1, 2, 4])       // instanceof Lazy.ArrayLikeSequence
   * Lazy({ foo: "bar" })  // instanceof Lazy.ObjectLikeSequence
   * Lazy("hello, world!") // instanceof Lazy.StringLikeSequence
   * Lazy()                // sequence: []
   * Lazy(null)            // sequence: []
   */
  function Lazy(source) {
    if (source instanceof Array) {
      return new ArrayWrapper(source);
    } else if (typeof source === "string") {
      return new StringWrapper(source);
    } else if (source instanceof Sequence) {
      return source;
    }

    if (Lazy.extensions) {
      var extensions = Lazy.extensions, length = extensions.length, result;
      while (!result && length--) {
        result = extensions[length](source);
      }
      if (result) {
        return result;
      }
    }

    return new ObjectWrapper(source);
  }

  Lazy.VERSION = '0.3.2';

  /*** Utility methods of questionable value ***/

  Lazy.noop = function noop() {};
  Lazy.identity = function identity(x) { return x; };

  /**
   * Provides a stricter version of {@link Lazy} which throws an error when
   * attempting to wrap `null`, `undefined`, or numeric or boolean values as a
   * sequence.
   *
   * @public
   * @returns {Function} A stricter version of the {@link Lazy} helper function.
   *
   * @examples
   * var Strict = Lazy.strict();
   *
   * Strict()                  // throws
   * Strict(null)              // throws
   * Strict(true)              // throws
   * Strict(5)                 // throws
   * Strict([1, 2, 3])         // instanceof Lazy.ArrayLikeSequence
   * Strict({ foo: "bar" })    // instanceof Lazy.ObjectLikeSequence
   * Strict("hello, world!")   // instanceof Lazy.StringLikeSequence
   *
   * // Let's also ensure the static functions are still there.
   * Strict.range(3)           // sequence: [0, 1, 2]
   * Strict.generate(Date.now) // instanceof Lazy.GeneratedSequence
   */
  Lazy.strict = function strict() {
    function StrictLazy(source) {
      if (source == null) {
        throw "You cannot wrap null or undefined using Lazy.";
      }

      if (typeof source === "number" || typeof source === "boolean") {
        throw "You cannot wrap primitive values using Lazy.";
      }

      return Lazy(source);
    };

    Lazy(Lazy).each(function(property, name) {
      StrictLazy[name] = property;
    });

    return StrictLazy;
  };

  /**
   * The `Sequence` object provides a unified API encapsulating the notion of
   * zero or more consecutive elements in a collection, stream, etc.
   *
   * Lazy evaluation
   * ---------------
   *
   * Generally speaking, creating a sequence should not be an expensive operation,
   * and should not iterate over an underlying source or trigger any side effects.
   * This means that chaining together methods that return sequences incurs only
   * the cost of creating the `Sequence` objects themselves and not the cost of
   * iterating an underlying data source multiple times.
   *
   * The following code, for example, creates 4 sequences and does nothing with
   * `source`:
   *
   *     var seq = Lazy(source) // 1st sequence
   *       .map(func)           // 2nd
   *       .filter(pred)        // 3rd
   *       .reverse();          // 4th
   *
   * Lazy's convention is to hold off on iterating or otherwise *doing* anything
   * (aside from creating `Sequence` objects) until you call `each`:
   *
   *     seq.each(function(x) {  });
   *
   * Defining custom sequences
   * -------------------------
   *
   * Defining your own type of sequence is relatively simple:
   *
   * 1. Pass a *method name* and an object containing *function overrides* to
   *    {@link Sequence.define}. If the object includes a function called `init`,
   *    this function will be called upon initialization.
   * 2. The object should include at least either a `getIterator` method or an
   *    `each` method. The former supports both asynchronous and synchronous
   *    iteration, but is slightly more cumbersome to implement. The latter
   *    supports synchronous iteration and can be automatically implemented in
   *    terms of the former. You can also implement both if you want, e.g. to
   *    optimize performance. For more info, see {@link Iterator} and
   *    {@link AsyncSequence}.
   *
   * As a trivial example, the following code defines a new method, `sample`,
   * which randomly may or may not include each element from its parent.
   *
   *     Lazy.Sequence.define("sample", {
   *       each: function(fn) {
   *         return this.parent.each(function(e) {
   *           // 50/50 chance of including this element.
   *           if (Math.random() > 0.5) {
   *             return fn(e);
   *           }
   *         });
   *       }
   *     });
   *
   * (Of course, the above could also easily have been implemented using
   * {@link #filter} instead of creating a custom sequence. But I *did* say this
   * was a trivial example, to be fair.)
   *
   * Now it will be possible to create this type of sequence from any parent
   * sequence by calling the method name you specified. In other words, you can
   * now do this:
   *
   *     Lazy(arr).sample();
   *     Lazy(arr).map(func).sample();
   *     Lazy(arr).map(func).filter(pred).sample();
   *
   * Etc., etc.
   *
   * @public
   * @constructor
   */
  function Sequence() {}

  /**
   * Create a new constructor function for a type inheriting from `Sequence`.
   *
   * @public
   * @param {string|Array.<string>} methodName The name(s) of the method(s) to be
   *     used for constructing the new sequence. The method will be attached to
   *     the `Sequence` prototype so that it can be chained with any other
   *     sequence methods, like {@link #map}, {@link #filter}, etc.
   * @param {Object} overrides An object containing function overrides for this
   *     new sequence type. **Must** include either `getIterator` or `each` (or
   *     both). *May* include an `init` method as well. For these overrides,
   *     `this` will be the new sequence, and `this.parent` will be the base
   *     sequence from which the new sequence was constructed.
   * @returns {Function} A constructor for a new type inheriting from `Sequence`.
   *
   * @examples
   * // This sequence type logs every element to the specified logger as it
   * // iterates over it.
   * Lazy.Sequence.define("verbose", {
   *   init: function(logger) {
   *     this.logger = logger;
   *   },
   *
   *   each: function(fn) {
   *     var logger = this.logger;
   *     return this.parent.each(function(e, i) {
   *       logger(e);
   *       return fn(e, i);
   *     });
   *   }
   * });
   *
   * Lazy([1, 2, 3]).verbose(logger).each(Lazy.noop) // calls logger 3 times
   */
  Sequence.define = function define(methodName, overrides) {
    if (!overrides || (!overrides.getIterator && !overrides.each)) {
      throw "A custom sequence must implement *at least* getIterator or each!";
    }

    return defineSequenceType(Sequence, methodName, overrides);
  };

  /**
   * Gets the number of elements in the sequence. In some cases, this may
   * require eagerly evaluating the sequence.
   *
   * @public
   * @returns {number} The number of elements in the sequence.
   *
   * @examples
   * Lazy([1, 2, 3]).size();                 // => 3
   * Lazy([1, 2]).map(Lazy.identity).size(); // => 2
   * Lazy([1, 2, 3]).reject(isEven).size();  // => 2
   * Lazy([1, 2, 3]).take(1).size();         // => 1
   * Lazy({ foo: 1, bar: 2 }).size();        // => 2
   * Lazy('hello').size();                   // => 5
   */
  Sequence.prototype.size = function size() {
    return this.getIndex().length();
  };

  /**
   * Creates an {@link Iterator} object with two methods, `moveNext` -- returning
   * true or false -- and `current` -- returning the current value.
   *
   * This method is used when asynchronously iterating over sequences. Any type
   * inheriting from `Sequence` must implement this method or it can't support
   * asynchronous iteration.
   *
   * Note that **this method is not intended to be used directly by application
   * code.** Rather, it is intended as a means for implementors to potentially
   * define custom sequence types that support either synchronous or
   * asynchronous iteration.
   *
   * @public
   * @returns {Iterator} An iterator object.
   *
   * @examples
   * var iterator = Lazy([1, 2]).getIterator();
   *
   * iterator.moveNext(); // => true
   * iterator.current();  // => 1
   * iterator.moveNext(); // => true
   * iterator.current();  // => 2
   * iterator.moveNext(); // => false
   */
  Sequence.prototype.getIterator = function getIterator() {
    return new Iterator(this);
  };

  /**
   * Gets the root sequence underlying the current chain of sequences.
   */
  Sequence.prototype.root = function root() {
    return this.parent.root();
  };

  /**
   * Evaluates the sequence and produces an appropriate value (an array in most
   * cases, an object for {@link ObjectLikeSequence}s or a string for
   * {@link StringLikeSequence}s).
   */
  Sequence.prototype.value = function value() {
    return this.toArray();
  };

  /**
   * Applies the current transformation chain to a given source.
   *
   * @examples
   * var sequence = Lazy([])
   *   .map(function(x) { return x * -1; })
   *   .filter(function(x) { return x % 2 === 0; });
   *
   * sequence.apply([1, 2, 3, 4]); // => [-2, -4]
   */
  Sequence.prototype.apply = function apply(source) {
    var root = this.root(),
        previousSource = root.source,
        result;

    try {
      root.source = source;
      result = this.value();
    } finally {
      root.source = previousSource;
    }

    return result;
  };

  /**
   * The Iterator object provides an API for iterating over a sequence.
   *
   * The purpose of the `Iterator` type is mainly to offer an agnostic way of
   * iterating over a sequence -- either synchronous (i.e. with a `while` loop)
   * or asynchronously (with recursive calls to either `setTimeout` or --- if
   * available --- `setImmediate`). It is not intended to be used directly by
   * application code.
   *
   * @public
   * @constructor
   * @param {Sequence} sequence The sequence to iterate over.
   */
  function Iterator(sequence) {
    this.sequence = sequence;
    this.index    = -1;
  }

  /**
   * Gets the current item this iterator is pointing to.
   *
   * @public
   * @returns {*} The current item.
   */
  Iterator.prototype.current = function current() {
    return this.cachedIndex && this.cachedIndex.get(this.index);
  };

  /**
   * Moves the iterator to the next item in a sequence, if possible.
   *
   * @public
   * @returns {boolean} True if the iterator is able to move to a new item, or else
   *     false.
   */
  Iterator.prototype.moveNext = function moveNext() {
    var cachedIndex = this.cachedIndex;

    if (!cachedIndex) {
      cachedIndex = this.cachedIndex = this.sequence.getIndex();
    }

    if (this.index >= cachedIndex.length() - 1) {
      return false;
    }

    ++this.index;
    return true;
  };

  /**
   * Creates an array snapshot of a sequence.
   *
   * Note that for indefinite sequences, this method may raise an exception or
   * (worse) cause the environment to hang.
   *
   * @public
   * @returns {Array} An array containing the current contents of the sequence.
   *
   * @examples
   * Lazy([1, 2, 3]).toArray() // => [1, 2, 3]
   */
  Sequence.prototype.toArray = function toArray() {
    return this.reduce(function(arr, element) {
      arr.push(element);
      return arr;
    }, []);
  };

  /**
   * Provides an indexed view into the sequence.
   *
   * For sequences that are already indexed, this will simply return the
   * sequence. For non-indexed sequences, this will eagerly evaluate the
   * sequence and cache the result (so subsequent calls will not create
   * additional arrays).
   *
   * @returns {ArrayLikeSequence} A sequence containing the current contents of
   *     the sequence.
   *
   * @examples
   * Lazy([1, 2, 3]).filter(isEven)            // instanceof Lazy.Sequence
   * Lazy([1, 2, 3]).filter(isEven).getIndex() // instanceof Lazy.ArrayLikeSequence
   */
  Sequence.prototype.getIndex = function getIndex() {
    if (!this.cachedIndex) {
      this.cachedIndex = new ArrayWrapper(this.toArray());
    }
    return this.cachedIndex;
  };

  /**
   * Provides an indexed, memoized view into the sequence. This will cache the
   * result whenever the sequence is first iterated, so that subsequent
   * iterations will access the same element objects.
   *
   * @public
   * @returns {ArrayLikeSequence} An indexed, memoized sequence containing this
   *     sequence's elements, cached after the first iteration.
   *
   * @example
   * function createObject() { return new Object(); }
   *
   * var plain    = Lazy.generate(createObject, 10),
   *     memoized = Lazy.generate(createObject, 10).memoize();
   *
   * plain.toArray()[0] === plain.toArray()[0];       // => false
   * memoized.toArray()[0] === memoized.toArray()[0]; // => true
   */
  Sequence.prototype.memoize = function memoize() {
    return new MemoizedSequence(this);
  };

  /**
   * @constructor
   */
  function MemoizedSequence(parent) {
    this.parent = parent;
  }

  // MemoizedSequence needs to have its prototype set up after ArrayLikeSequence

  /**
   * Creates an object from a sequence of key/value pairs.
   *
   * @public
   * @returns {Object} An object with keys and values corresponding to the pairs
   *     of elements in the sequence.
   *
   * @examples
   * var details = [
   *   ["first", "Dan"],
   *   ["last", "Tao"],
   *   ["age", 29]
   * ];
   *
   * Lazy(details).toObject() // => { first: "Dan", last: "Tao", age: 29 }
   */
  Sequence.prototype.toObject = function toObject() {
    return this.reduce(function(object, pair) {
      object[pair[0]] = pair[1];
      return object;
    }, {});
  };

  /**
   * Iterates over this sequence and executes a function for every element.
   *
   * @public
   * @aka forEach
   * @param {Function} fn The function to call on each element in the sequence.
   *     Return false from the function to end the iteration.
   *
   * @examples
   * Lazy([1, 2, 3, 4]).each(fn) // calls fn 4 times
   */
  Sequence.prototype.each = function each(fn) {
    var iterator = this.getIterator(),
        i = -1;

    while (iterator.moveNext()) {
      if (fn(iterator.current(), ++i) === false) {
        return false;
      }
    }

    return true;
  };

  Sequence.prototype.forEach = function forEach(fn) {
    return this.each(fn);
  };

  /**
   * Creates a new sequence whose values are calculated by passing this sequence's
   * elements through some mapping function.
   *
   * @public
   * @aka collect
   * @param {Function} mapFn The mapping function used to project this sequence's
   *     elements onto a new sequence.
   * @returns {Sequence} The new sequence.
   *
   * @examples
   * Lazy([]).map(increment)        // sequence: []
   * Lazy([1, 2, 3]).map(increment) // sequence: [2, 3, 4]
   *
   * @benchmarks
   * function increment(x) { return x + 1; }
   *
   * var smArr = Lazy.range(10).toArray(),
   *     lgArr = Lazy.range(100).toArray();
   *
   * Lazy(smArr).map(increment).each(Lazy.noop) // lazy - 10 elements
   * Lazy(lgArr).map(increment).each(Lazy.noop) // lazy - 100 elements
   * _.each(_.map(smArr, increment), _.noop)    // lodash - 10 elements
   * _.each(_.map(lgArr, increment), _.noop)    // lodash - 100 elements
   */
  Sequence.prototype.map = function map(mapFn) {
    return new MappedSequence(this, createCallback(mapFn));
  };

  Sequence.prototype.collect = function collect(mapFn) {
    return this.map(mapFn);
  };

  /**
   * @constructor
   */
  function MappedSequence(parent, mapFn) {
    this.parent = parent;
    this.mapFn  = mapFn;
  }

  MappedSequence.prototype = new Sequence();

  MappedSequence.prototype.getIterator = function getIterator() {
    return new MappingIterator(this.parent, this.mapFn);
  };

  MappedSequence.prototype.each = function each(fn) {
    var mapFn = this.mapFn;
    return this.parent.each(function(e, i) {
      return fn(mapFn(e, i), i);
    });
  };

  /**
   * @constructor
   */
  function MappingIterator(sequence, mapFn) {
    this.iterator = sequence.getIterator();
    this.mapFn    = mapFn;
    this.index    = -1;
  }

  MappingIterator.prototype.current = function current() {
    return this.mapFn(this.iterator.current(), this.index);
  };

  MappingIterator.prototype.moveNext = function moveNext() {
    if (this.iterator.moveNext()) {
      ++this.index;
      return true;
    }

    return false;
  };

  /**
   * Creates a new sequence whose values are calculated by accessing the specified
   * property from each element in this sequence.
   *
   * @public
   * @param {string} propertyName The name of the property to access for every
   *     element in this sequence.
   * @returns {Sequence} The new sequence.
   *
   * @examples
   * var people = [
   *   { first: "Dan", last: "Tao" },
   *   { first: "Bob", last: "Smith" }
   * ];
   *
   * Lazy(people).pluck("last") // sequence: ["Tao", "Smith"]
   */
  Sequence.prototype.pluck = function pluck(property) {
    return this.map(property);
  };

  /**
   * Creates a new sequence whose values are calculated by invoking the specified
   * function on each element in this sequence.
   *
   * @public
   * @param {string} methodName The name of the method to invoke for every element
   *     in this sequence.
   * @returns {Sequence} The new sequence.
   *
   * @examples
   * function Person(first, last) {
   *   this.fullName = function fullName() {
   *     return first + " " + last;
   *   };
   * }
   *
   * var people = [
   *   new Person("Dan", "Tao"),
   *   new Person("Bob", "Smith")
   * ];
   *
   * Lazy(people).invoke("fullName") // sequence: ["Dan Tao", "Bob Smith"]
   */
  Sequence.prototype.invoke = function invoke(methodName) {
    return this.map(function(e) {
      return e[methodName]();
    });
  };

  /**
   * Creates a new sequence whose values are the elements of this sequence which
   * satisfy the specified predicate.
   *
   * @public
   * @aka select
   * @param {Function} filterFn The predicate to call on each element in this
   *     sequence, which returns true if the element should be included.
   * @returns {Sequence} The new sequence.
   *
   * @examples
   * var numbers = [1, 2, 3, 4, 5, 6];
   *
   * Lazy(numbers).filter(isEven) // sequence: [2, 4, 6]
   *
   * @benchmarks
   * function isEven(x) { return x % 2 === 0; }
   *
   * var smArr = Lazy.range(10).toArray(),
   *     lgArr = Lazy.range(100).toArray();
   *
   * Lazy(smArr).filter(isEven).each(Lazy.noop) // lazy - 10 elements
   * Lazy(lgArr).filter(isEven).each(Lazy.noop) // lazy - 100 elements
   * _.each(_.filter(smArr, isEven), _.noop)    // lodash - 10 elements
   * _.each(_.filter(lgArr, isEven), _.noop)    // lodash - 100 elements
   */
  Sequence.prototype.filter = function filter(filterFn) {
    return new FilteredSequence(this, createCallback(filterFn));
  };

  Sequence.prototype.select = function select(filterFn) {
    return this.filter(filterFn);
  };

  /**
   * @constructor
   */
  function FilteredSequence(parent, filterFn) {
    this.parent   = parent;
    this.filterFn = filterFn;
  }

  FilteredSequence.prototype = new Sequence();

  FilteredSequence.prototype.getIterator = function getIterator() {
    return new FilteringIterator(this.parent, this.filterFn);
  };

  FilteredSequence.prototype.each = function each(fn) {
    var filterFn = this.filterFn;

    return this.parent.each(function(e, i) {
      if (filterFn(e, i)) {
        return fn(e, i);
      }
    });
  };

  FilteredSequence.prototype.reverse = function reverse() {
    return this.parent.reverse().filter(this.filterFn);
  };

  /**
   * @constructor
   */
  function FilteringIterator(sequence, filterFn) {
    this.iterator = sequence.getIterator();
    this.filterFn = filterFn;
    this.index    = 0;
  }

  FilteringIterator.prototype.current = function current() {
    return this.value;
  };

  FilteringIterator.prototype.moveNext = function moveNext() {
    var iterator = this.iterator,
        filterFn = this.filterFn,
        value;

    while (iterator.moveNext()) {
      value = iterator.current();
      if (filterFn(value, this.index++)) {
        this.value = value;
        return true;
      }
    }

    this.value = undefined;
    return false;
  };

  /**
   * Creates a new sequence whose values exclude the elements of this sequence
   * identified by the specified predicate.
   *
   * @public
   * @param {Function} rejectFn The predicate to call on each element in this
   *     sequence, which returns true if the element should be omitted.
   * @returns {Sequence} The new sequence.
   *
   * @examples
   * Lazy([1, 2, 3, 4, 5]).reject(isEven)              // sequence: [1, 3, 5]
   * Lazy([{ foo: 1 }, { bar: 2 }]).reject('foo')      // sequence: [{ bar: 2 }]
   * Lazy([{ foo: 1 }, { foo: 2 }]).reject({ foo: 2 }) // sequence: [{ foo: 1 }]
   */
  Sequence.prototype.reject = function reject(rejectFn) {
    rejectFn = createCallback(rejectFn);
    return this.filter(function(e) { return !rejectFn(e); });
  };

  /**
   * Creates a new sequence whose values have the specified type, as determined
   * by the `typeof` operator.
   *
   * @public
   * @param {string} type The type of elements to include from the underlying
   *     sequence, i.e. where `typeof [element] === [type]`.
   * @returns {Sequence} The new sequence, comprising elements of the specified
   *     type.
   *
   * @examples
   * Lazy([1, 2, 'foo', 'bar']).ofType('number')  // sequence: [1, 2]
   * Lazy([1, 2, 'foo', 'bar']).ofType('string')  // sequence: ['foo', 'bar']
   * Lazy([1, 2, 'foo', 'bar']).ofType('boolean') // sequence: []
   */
  Sequence.prototype.ofType = function ofType(type) {
    return this.filter(function(e) { return typeof e === type; });
  };

  /**
   * Creates a new sequence whose values are the elements of this sequence with
   * property names and values matching those of the specified object.
   *
   * @public
   * @param {Object} properties The properties that should be found on every
   *     element that is to be included in this sequence.
   * @returns {Sequence} The new sequence.
   *
   * @examples
   * var people = [
   *   { first: "Dan", last: "Tao" },
   *   { first: "Bob", last: "Smith" }
   * ];
   *
   * Lazy(people).where({ first: "Dan" }) // sequence: [{ first: "Dan", last: "Tao" }]
   *
   * @benchmarks
   * var animals = ["dog", "cat", "mouse", "horse", "pig", "snake"];
   *
   * Lazy(animals).where({ length: 3 }).each(Lazy.noop) // lazy
   * _.each(_.where(animals, { length: 3 }), _.noop)    // lodash
   */
  Sequence.prototype.where = function where(properties) {
    return this.filter(properties);
  };

  /**
   * Creates a new sequence with the same elements as this one, but to be iterated
   * in the opposite order.
   *
   * Note that in some (but not all) cases, the only way to create such a sequence
   * may require iterating the entire underlying source when `each` is called.
   *
   * @public
   * @returns {Sequence} The new sequence.
   *
   * @examples
   * Lazy([1, 2, 3]).reverse() // sequence: [3, 2, 1]
   * Lazy([]).reverse()        // sequence: []
   */
  Sequence.prototype.reverse = function reverse() {
    return new ReversedSequence(this);
  };

  /**
   * @constructor
   */
  function ReversedSequence(parent) {
    this.parent = parent;
  }

  ReversedSequence.prototype = new Sequence();

  ReversedSequence.prototype.getIterator = function getIterator() {
    return new ReversedIterator(this.parent);
  };

  /**
   * @constuctor
   */
  function ReversedIterator(sequence) {
    this.sequence = sequence;
  }

  ReversedIterator.prototype.current = function current() {
    return this.sequence.getIndex().get(this.index);
  };

  ReversedIterator.prototype.moveNext = function moveNext() {
    var indexed = this.sequence.getIndex(),
        length  = indexed.length();

    if (typeof this.index === "undefined") {
      this.index = length;
    }

    return (--this.index >= 0);
  };

  /**
   * Creates a new sequence with all of the elements of this one, plus those of
   * the given array(s).
   *
   * @public
   * @param {...*} var_args One or more values (or arrays of values) to use for
   *     additional items after this sequence.
   * @returns {Sequence} The new sequence.
   *
   * @examples
   * var left  = [1, 2, 3];
   * var right = [4, 5, 6];
   *
   * Lazy(left).concat(right)         // sequence: [1, 2, 3, 4, 5, 6]
   * Lazy(left).concat(Lazy(right))   // sequence: [1, 2, 3, 4, 5, 6]
   * Lazy(left).concat(right, [7, 8]) // sequence: [1, 2, 3, 4, 5, 6, 7, 8]
   */
  Sequence.prototype.concat = function concat(var_args) {
    return new ConcatenatedSequence(this, arraySlice.call(arguments, 0));
  };

  /**
   * @constructor
   */
  function ConcatenatedSequence(parent, arrays) {
    this.parent = parent;
    this.arrays = arrays;
  }

  ConcatenatedSequence.prototype = new Sequence();

  ConcatenatedSequence.prototype.each = function each(fn) {
    var done = false,
        i = 0;

    this.parent.each(function(e) {
      if (fn(e, i++) === false) {
        done = true;
        return false;
      }
    });

    if (!done) {
      Lazy(this.arrays).flatten().each(function(e) {
        if (fn(e, i++) === false) {
          return false;
        }
      });
    }
  };

  /**
   * Creates a new sequence comprising the first N elements from this sequence, OR
   * (if N is `undefined`) simply returns the first element of this sequence.
   *
   * @public
   * @aka head, take
   * @param {number=} count The number of elements to take from this sequence. If
   *     this value exceeds the length of the sequence, the resulting sequence
   *     will be essentially the same as this one.
   * @returns {*} The new sequence (or the first element from this sequence if
   *     no count was given).
   *
   * @examples
   * function powerOfTwo(exp) {
   *   return Math.pow(2, exp);
   * }
   *
   * Lazy.generate(powerOfTwo).first()          // => 1
   * Lazy.generate(powerOfTwo).first(5)         // sequence: [1, 2, 4, 8, 16]
   * Lazy.generate(powerOfTwo).skip(2).first()  // => 4
   * Lazy.generate(powerOfTwo).skip(2).first(2) // sequence: [4, 8]
   */
  Sequence.prototype.first = function first(count) {
    if (typeof count === "undefined") {
      return getFirst(this);
    }
    return new TakeSequence(this, count);
  };

  Sequence.prototype.head =
  Sequence.prototype.take = function (count) {
    return this.first(count);
  };

  /**
   * @constructor
   */
  function TakeSequence(parent, count) {
    this.parent = parent;
    this.count  = count;
  }

  TakeSequence.prototype = new Sequence();

  TakeSequence.prototype.getIterator = function getIterator() {
    return new TakeIterator(this.parent, this.count);
  };

  TakeSequence.prototype.each = function each(fn) {
    var count = this.count,
        i     = 0;

    this.parent.each(function(e) {
      var result;
      if (i < count) { result = fn(e, i); }
      if (++i >= count) { return false; }
      return result;
    });
  };

  /**
   * @constructor
   */
  function TakeIterator(sequence, count) {
    this.iterator = sequence.getIterator();
    this.count    = count;
  }

  TakeIterator.prototype.current = function current() {
    return this.iterator.current();
  };

  TakeIterator.prototype.moveNext = function moveNext() {
    return ((--this.count >= 0) && this.iterator.moveNext());
  };

  /**
   * Creates a new sequence comprising the elements from the head of this sequence
   * that satisfy some predicate. Once an element is encountered that doesn't
   * satisfy the predicate, iteration will stop.
   *
   * @public
   * @param {Function} predicate
   * @returns {Sequence} The new sequence
   *
   * @examples
   * function lessThan(x) {
   *   return function(y) {
   *     return y < x;
   *   };
   * }
   *
   * Lazy([1, 2, 3, 4]).takeWhile(lessThan(3)) // sequence: [1, 2]
   * Lazy([1, 2, 3, 4]).takeWhile(lessThan(0)) // sequence: []
   */
  Sequence.prototype.takeWhile = function takeWhile(predicate) {
    return new TakeWhileSequence(this, predicate);
  };

  /**
   * @constructor
   */
  function TakeWhileSequence(parent, predicate) {
    this.parent    = parent;
    this.predicate = predicate;
  }

  TakeWhileSequence.prototype = new Sequence();

  TakeWhileSequence.prototype.each = function each(fn) {
    var predicate = this.predicate;

    this.parent.each(function(e) {
      return predicate(e) && fn(e);
    });
  };

  /**
   * Creates a new sequence comprising all but the last N elements of this
   * sequence.
   *
   * @public
   * @param {number=} count The number of items to omit from the end of the
   *     sequence (defaults to 1).
   * @returns {Sequence} The new sequence.
   *
   * @examples
   * Lazy([1, 2, 3, 4]).initial()                    // sequence: [1, 2, 3]
   * Lazy([1, 2, 3, 4]).initial(2)                   // sequence: [1, 2]
   * Lazy([1, 2, 3]).filter(Lazy.identity).initial() // sequence: [1, 2]
   */
  Sequence.prototype.initial = function initial(count) {
    if (typeof count === "undefined") {
      count = 1;
    }
    return this.take(this.getIndex().length() - count);
  };

  /**
   * Creates a new sequence comprising the last N elements of this sequence, OR
   * (if N is `undefined`) simply returns the last element of this sequence.
   *
   * @public
   * @param {number=} count The number of items to take from the end of the
   *     sequence.
   * @returns {*} The new sequence (or the last element from this sequence
   *     if no count was given).
   *
   * @examples
   * Lazy([1, 2, 3]).last()                 // => 3
   * Lazy([1, 2, 3]).last(2)                // sequence: [2, 3]
   * Lazy([1, 2, 3]).filter(isEven).last(2) // sequence: [2]
   */
  Sequence.prototype.last = function last(count) {
    if (typeof count === "undefined") {
      return this.reverse().first();
    }
    return this.reverse().take(count).reverse();
  };

  /**
   * Returns the first element in this sequence with property names and values
   * matching those of the specified object.
   *
   * @public
   * @param {Object} properties The properties that should be found on some
   *     element in this sequence.
   * @returns {*} The found element, or `undefined` if none exists in this
   *     sequence.
   *
   * @examples
   * var words = ["foo", "bar"];
   *
   * Lazy(words).findWhere({ 0: "f" }); // => "foo"
   * Lazy(words).findWhere({ 0: "z" }); // => undefined
   */
  Sequence.prototype.findWhere = function findWhere(properties) {
    return this.where(properties).first();
  };

  /**
   * Creates a new sequence comprising all but the first N elements of this
   * sequence.
   *
   * @public
   * @aka skip, tail, rest
   * @param {number=} count The number of items to omit from the beginning of the
   *     sequence (defaults to 1).
   * @returns {Sequence} The new sequence.
   *
   * @examples
   * Lazy([1, 2, 3, 4]).rest()  // sequence: [2, 3, 4]
   * Lazy([1, 2, 3, 4]).rest(0) // sequence: [1, 2, 3, 4]
   * Lazy([1, 2, 3, 4]).rest(2) // sequence: [3, 4]
   * Lazy([1, 2, 3, 4]).rest(5) // sequence: []
   */
  Sequence.prototype.rest = function rest(count) {
    return new DropSequence(this, count);
  };

  Sequence.prototype.skip =
  Sequence.prototype.tail =
  Sequence.prototype.drop = function drop(count) {
    return this.rest(count);
  };

  /**
   * @constructor
   */
  function DropSequence(parent, count) {
    this.parent = parent;
    this.count  = typeof count === "number" ? count : 1;
  }

  DropSequence.prototype = new Sequence();

  DropSequence.prototype.each = function each(fn) {
    var count   = this.count,
        dropped = 0,
        i       = 0;

    this.parent.each(function(e) {
      if (dropped++ < count) { return; }
      return fn(e, i++);
    });
  };

  /**
   * Creates a new sequence comprising the elements from this sequence *after*
   * those that satisfy some predicate. The sequence starts with the first
   * element that does not match the predicate.
   *
   * @public
   * @aka skipWhile
   * @param {Function} predicate
   * @returns {Sequence} The new sequence
   */
  Sequence.prototype.dropWhile = function dropWhile(predicate) {
    return new DropWhileSequence(this, predicate);
  };

  Sequence.prototype.skipWhile = function skipWhile(predicate) {
    return this.dropWhile(predicate);
  };

  /**
   * @constructor
   */
  function DropWhileSequence(parent, predicate) {
    this.parent    = parent;
    this.predicate = predicate;
  }

  DropWhileSequence.prototype = new Sequence();

  DropWhileSequence.prototype.each = function each(fn) {
    var predicate = this.predicate,
        done      = false;

    this.parent.each(function(e) {
      if (!done) {
        if (predicate(e)) {
          return;
        }

        done = true;
      }

      return fn(e);
    });
  };

  /**
   * Creates a new sequence with the same elements as this one, but ordered
   * according to the values returned by the specified function.
   *
   * @public
   * @param {Function} sortFn The function to call on the elements in this
   *     sequence, in order to sort them.
   * @returns {Sequence} The new sequence.
   *
   * @examples
   * function population(country) {
   *   return country.pop;
   * }
   *
   * function area(country) {
   *   return country.sqkm;
   * }
   *
   * var countries = [
   *   { name: "USA", pop: 320000000, sqkm: 9600000 },
   *   { name: "Brazil", pop: 194000000, sqkm: 8500000 },
   *   { name: "Nigeria", pop: 174000000, sqkm: 924000 },
   *   { name: "China", pop: 1350000000, sqkm: 9700000 },
   *   { name: "Russia", pop: 143000000, sqkm: 17000000 },
   *   { name: "Australia", pop: 23000000, sqkm: 7700000 }
   * ];
   *
   * Lazy(countries).sortBy(population).last(3).pluck('name') // sequence: ["Brazil", "USA", "China"]
   * Lazy(countries).sortBy(area).last(3).pluck('name')       // sequence: ["USA", "China", "Russia"]
   *
   * @benchmarks
   * var randoms = Lazy.generate(Math.random).take(100).toArray();
   *
   * Lazy(randoms).sortBy(Lazy.identity).each(Lazy.noop) // lazy
   * _.each(_.sortBy(randoms, Lazy.identity), _.noop)    // lodash
   */
  Sequence.prototype.sortBy = function sortBy(sortFn) {
    return new SortedSequence(this, sortFn);
  };

  /**
   * @constructor
   */
  function SortedSequence(parent, sortFn) {
    this.parent = parent;
    this.sortFn = sortFn;
  }

  SortedSequence.prototype = new Sequence();

  SortedSequence.prototype.each = function each(fn) {
    var sortFn = createCallback(this.sortFn),
        sorted = this.parent.toArray(),
        i = -1;

    sorted.sort(function(x, y) { return compare(x, y, sortFn); });

    return forEach(sorted, fn);
  };

  /**
   * Creates a new {@link ObjectLikeSequence} comprising the elements in this
   * one, grouped together according to some key. The value associated with each
   * key in the resulting object-like sequence is an array containing all of
   * the elements in this sequence with that key.
   *
   * @public
   * @param {Function|string} keyFn The function to call on the elements in this
   *     sequence to obtain a key by which to group them, or a string representing
   *     a parameter to read from all the elements in this sequence.
   * @returns {Sequence} The new sequence.
   *
   * @examples
   * function oddOrEven(x) {
   *   return x % 2 === 0 ? 'even' : 'odd';
   * }
   *
   * var numbers = [1, 2, 3, 4, 5];
   *
   * Lazy(numbers).groupBy(oddOrEven)            // sequence: { odd: [1, 3, 5], even: [2, 4] }
   * Lazy(numbers).groupBy(oddOrEven).get("odd") // => [1, 3, 5]
   * Lazy(numbers).groupBy(oddOrEven).get("foo") // => undefined
   */
  Sequence.prototype.groupBy = function groupBy(keyFn) {
    return new GroupedSequence(this, keyFn);
  };

  /**
   * @constructor
   */
  function GroupedSequence(parent, keyFn) {
    this.parent = parent;
    this.keyFn  = keyFn;
  }

  // GroupedSequence must have its prototype set after ObjectLikeSequence has
  // been fully initialized.

  /**
   * Creates a new {@link ObjectLikeSequence} containing the unique keys of all
   * the elements in this sequence, each paired with the number of elements
   * in this sequence having that key.
   *
   * @public
   * @param {Function|string} keyFn The function to call on the elements in this
   *     sequence to obtain a key by which to count them, or a string representing
   *     a parameter to read from all the elements in this sequence.
   * @returns {Sequence} The new sequence.
   *
   * @examples
   * function oddOrEven(x) {
   *   return x % 2 === 0 ? 'even' : 'odd';
   * }
   *
   * var numbers = [1, 2, 3, 4, 5];
   *
   * Lazy(numbers).countBy(oddOrEven)            // sequence: { odd: 3, even: 2 }
   * Lazy(numbers).countBy(oddOrEven).get("odd") // => 3
   * Lazy(numbers).countBy(oddOrEven).get("foo") // => undefined
   */
  Sequence.prototype.countBy = function countBy(keyFn) {
    return new CountedSequence(this, keyFn);
  };

  /**
   * @constructor
   */
  function CountedSequence(parent, keyFn) {
    this.parent = parent;
    this.keyFn  = keyFn;
  }

  // CountedSequence, like GroupedSequence, must have its prototype set after
  // ObjectLikeSequence has been fully initialized.

  /**
   * Creates a new sequence with every unique element from this one appearing
   * exactly once (i.e., with duplicates removed).
   *
   * @public
   * @aka unique
   * @returns {Sequence} The new sequence.
   *
   * @examples
   * Lazy([1, 2, 2, 3, 3, 3]).uniq() // sequence: [1, 2, 3]
   *
   * @benchmarks
   * function randomOf(array) {
   *   return function() {
   *     return array[Math.floor(Math.random() * array.length)];
   *   };
   * }
   *
   * var mostUnique = Lazy.generate(randomOf(_.range(100)), 100).toArray(),
   *     someUnique = Lazy.generate(randomOf(_.range(50)), 100).toArray(),
   *     mostDupes  = Lazy.generate(randomOf(_.range(5)), 100).toArray();
   *
   * Lazy(mostUnique).uniq().each(Lazy.noop) // lazy - mostly unique elements
   * Lazy(someUnique).uniq().each(Lazy.noop) // lazy - some unique elements
   * Lazy(mostDupes).uniq().each(Lazy.noop)  // lazy - mostly duplicate elements
   * _.each(_.uniq(mostUnique), _.noop)      // lodash - mostly unique elements
   * _.each(_.uniq(someUnique), _.noop)      // lodash - some unique elements
   * _.each(_.uniq(mostDupes), _.noop)       // lodash - mostly duplicate elements
   */
  Sequence.prototype.uniq = function uniq(keyFn) {
    return new UniqueSequence(this, keyFn);
  };

  Sequence.prototype.unique = function unique(keyFn) {
    return this.uniq(keyFn);
  };

  /**
   * @constructor
   */
  function UniqueSequence(parent, keyFn) {
    this.parent = parent;
    this.keyFn  = keyFn;
  }

  UniqueSequence.prototype = new Sequence();

  UniqueSequence.prototype.each = function each(fn) {
    var cache = new Set(),
        keyFn = this.keyFn,
        i     = 0;

    if (keyFn) {
      keyFn = createCallback(keyFn);
      return this.parent.each(function(e) {
        if (cache.add(keyFn(e))) {
          return fn(e, i++);
        }
      });

    } else {
      return this.parent.each(function(e) {
        if (cache.add(e)) {
          return fn(e, i++);
        }
      });
    }
  };

  /**
   * Creates a new sequence by combining the elements from this sequence with
   * corresponding elements from the specified array(s).
   *
   * @public
   * @param {...Array} var_args One or more arrays of elements to combine with
   *     those of this sequence.
   * @returns {Sequence} The new sequence.
   *
   * @examples
   * Lazy([1, 2]).zip([3, 4]) // sequence: [[1, 3], [2, 4]]
   *
   * @benchmarks
   * var smArrL = Lazy.range(10).toArray(),
   *     smArrR = Lazy.range(10, 20).toArray(),
   *     lgArrL = Lazy.range(100).toArray(),
   *     lgArrR = Lazy.range(100, 200).toArray();
   *
   * Lazy(smArrL).zip(smArrR).each(Lazy.noop) // lazy - zipping 10-element arrays
   * Lazy(lgArrL).zip(lgArrR).each(Lazy.noop) // lazy - zipping 100-element arrays
   * _.each(_.zip(smArrL, smArrR), _.noop)    // lodash - zipping 10-element arrays
   * _.each(_.zip(lgArrL, lgArrR), _.noop)    // lodash - zipping 100-element arrays
   */
  Sequence.prototype.zip = function zip(var_args) {
    if (arguments.length === 1) {
      return new SimpleZippedSequence(this, (/** @type {Array} */ var_args));
    } else {
      return new ZippedSequence(this, arraySlice.call(arguments, 0));
    }
  };

  /**
   * @constructor
   */
  function ZippedSequence(parent, arrays) {
    this.parent = parent;
    this.arrays = arrays;
  }

  ZippedSequence.prototype = new Sequence();

  ZippedSequence.prototype.each = function each(fn) {
    var arrays = this.arrays,
        i = 0;
    this.parent.each(function(e) {
      var group = [e];
      for (var j = 0; j < arrays.length; ++j) {
        if (arrays[j].length > i) {
          group.push(arrays[j][i]);
        }
      }
      return fn(group, i++);
    });
  };

  /**
   * Creates a new sequence with the same elements as this one, in a randomized
   * order.
   *
   * @public
   * @returns {Sequence} The new sequence.
   *
   * @examples
   * Lazy([1, 2, 3, 4, 5]).shuffle() // the values [1, 2, 3, 4, 5] in any order
   */
  Sequence.prototype.shuffle = function shuffle() {
    return new ShuffledSequence(this);
  };

  /**
   * @constructor
   */
  function ShuffledSequence(parent) {
    this.parent = parent;
  }

  ShuffledSequence.prototype = new Sequence();

  ShuffledSequence.prototype.each = function each(fn) {
    var shuffled = this.parent.toArray(),
        floor = Math.floor,
        random = Math.random,
        j = 0;

    for (var i = shuffled.length - 1; i > 0; --i) {
      swap(shuffled, i, floor(random() * i) + 1);
      if (fn(shuffled[i], j++) === false) {
        return;
      }
    }
    fn(shuffled[0], j);
  };

  /**
   * Creates a new sequence with every element from this sequence, and with arrays
   * exploded so that a sequence of arrays (of arrays) becomes a flat sequence of
   * values.
   *
   * @public
   * @returns {Sequence} The new sequence.
   *
   * @examples
   * Lazy([1, [2, 3], [4, [5]]]).flatten() // sequence: [1, 2, 3, 4, 5]
   * Lazy([1, Lazy([2, 3])]).flatten()     // sequence: [1, 2, 3]
   */
  Sequence.prototype.flatten = function flatten() {
    return new FlattenedSequence(this);
  };

  /**
   * @constructor
   */
  function FlattenedSequence(parent) {
    this.parent = parent;
  }

  FlattenedSequence.prototype = new Sequence();

  FlattenedSequence.prototype.each = function each(fn) {
    var index = 0;

    return this.parent.each(function recurseVisitor(e) {
      if (e instanceof Array) {
        return forEach(e, recurseVisitor);
      }

      if (e instanceof Sequence) {
        return e.each(recurseVisitor);
      }

      return fn(e, index++);
    });
  };

  /**
   * Creates a new sequence with the same elements as this one, except for all
   * falsy values (`false`, `0`, `""`, `null`, and `undefined`).
   *
   * @public
   * @returns {Sequence} The new sequence.
   *
   * @examples
   * Lazy(["foo", null, "bar", undefined]).compact() // sequence: ["foo", "bar"]
   */
  Sequence.prototype.compact = function compact() {
    return this.filter(function(e) { return !!e; });
  };

  /**
   * Creates a new sequence with all the elements of this sequence that are not
   * also among the specified arguments.
   *
   * @public
   * @aka difference
   * @param {...*} var_args The values, or array(s) of values, to be excluded from the
   *     resulting sequence.
   * @returns {Sequence} The new sequence.
   *
   * @examples
   * Lazy([1, 2, 3, 4, 5]).without(2, 3)   // sequence: [1, 4, 5]
   * Lazy([1, 2, 3, 4, 5]).without([4, 5]) // sequence: [1, 2, 3]
   */
  Sequence.prototype.without = function without(var_args) {
    return new WithoutSequence(this, arraySlice.call(arguments, 0));
  };

  Sequence.prototype.difference = function difference(var_args) {
    return this.without.apply(this, arguments);
  };

  /**
   * @constructor
   */
  function WithoutSequence(parent, values) {
    this.parent = parent;
    this.values = values;
  }

  WithoutSequence.prototype = new Sequence();

  WithoutSequence.prototype.each = function each(fn) {
    var set = createSet(this.values),
        i = 0;
    return this.parent.each(function(e) {
      if (!set.contains(e)) {
        return fn(e, i++);
      }
    });
  };

  /**
   * Creates a new sequence with all the unique elements either in this sequence
   * or among the specified arguments.
   *
   * @public
   * @param {...*} var_args The values, or array(s) of values, to be additionally
   *     included in the resulting sequence.
   * @returns {Sequence} The new sequence.
   *
   * @examples
   * Lazy(["foo", "bar"]).union([])             // sequence: ["foo", "bar"]
   * Lazy(["foo", "bar"]).union(["bar", "baz"]) // sequence: ["foo", "bar", "baz"]
   */
  Sequence.prototype.union = function union(var_args) {
    return this.concat(var_args).uniq();
  };

  /**
   * Creates a new sequence with all the elements of this sequence that also
   * appear among the specified arguments.
   *
   * @public
   * @param {...*} var_args The values, or array(s) of values, in which elements
   *     from this sequence must also be included to end up in the resulting sequence.
   * @returns {Sequence} The new sequence.
   *
   * @examples
   * Lazy(["foo", "bar"]).intersection([])             // sequence: []
   * Lazy(["foo", "bar"]).intersection(["bar", "baz"]) // sequence: ["bar"]
   */
  Sequence.prototype.intersection = function intersection(var_args) {
    if (arguments.length === 1 && arguments[0] instanceof Array) {
      return new SimpleIntersectionSequence(this, (/** @type {Array} */ var_args));
    } else {
      return new IntersectionSequence(this, arraySlice.call(arguments, 0));
    }
  };

  /**
   * @constructor
   */
  function IntersectionSequence(parent, arrays) {
    this.parent = parent;
    this.arrays = arrays;
  }

  IntersectionSequence.prototype = new Sequence();

  IntersectionSequence.prototype.each = function each(fn) {
    var sets = Lazy(this.arrays).map(function(values) {
      return new UniqueMemoizer(Lazy(values).getIterator());
    });

    var setIterator = new UniqueMemoizer(sets.getIterator()),
        i = 0;

    return this.parent.each(function(e) {
      var includedInAll = true;
      setIterator.each(function(set) {
        if (!set.contains(e)) {
          includedInAll = false;
          return false;
        }
      });

      if (includedInAll) {
        return fn(e, i++);
      }