seq.js

lang.EmptyCons = {
    first: function() {return null;},
    rest:  function() {return lang.EmptyCons;},
    seq:   function() {return null;},
    toString: function() {return "()";}
}

lang.Cons = function(_first, _rest) {
    if (!_rest) { _rest = lang.EmptyCons; }
    this._first = _first;
    this._rest = _rest;
}

lang.Cons.prototype = {
    first: function() {return this._first;},
    rest: function()  {return this._rest;},
    seq:  function()  {return this;},
    toString: function() {return lang.printSeq(this);}
}

lang.ArraySeq = function(array, index) {
    if (index >= array.length) {
        return lang.EmptyCons
    }
    this._array = array;
    this._index = index;
}

lang.ArraySeq.prototype = {
    first: function() {return this._array[this._index]},
    rest: function() {return new lang.ArraySeq(this._array, this._index + 1)},
    seq: function() {return this},
    toString: function() {return lang.printSeq(this)}
}

lang.StringSeq = function(string, index) {
   if (index >= string.length) {
        return lang.EmptyCons;
    }
    this._string = string;
    this._index = index;
}

lang.StringSeq.prototype = {
    first: function() {return this._string.charAt(this._index)},
    rest: function() {return new lang.StringSeq(this._string, this._index + 1)},
    seq: function() {return this},
    toString: function() {return lang.printSeq(this)}
}

Array.prototype.seq = function() {
    return new lang.ArraySeq(this, 0)
}

String.prototype.seq = function() {
  return new lang.StringSeq(this, 0);
}

lang.cons = function(x, coll) {
    return new lang.Cons(x, coll.seq());
}

lang.first = function(coll) {
    return coll.seq().first();
}

lang.rest = function(coll) {
    return coll.seq().rest();
}

lang.seq = function(coll) {
  if (lang.isNil(coll)) return null;
  if (coll["seq"]) return coll.seq();
  if (lang.isNumber(coll)) throw "not seqable";
  if ("length" in coll) return new lang.ArraySeq(coll, 0);
  if (lang.isFunction(coll)) throw "not seqable";
  return new lang.ArraySeq(lang.objectToArray(coll), 0)
}