util.js

function LazySeq(fn, start) {
  var last;

  //functions to apply on realization
  var maps = [];

  //use lazy function definition
  this.next = function() {
    this.next = function() {
      return last = fn(last);
    };
    return last = start;
  };

  this.map = function(fn) {
    maps.push(fn);
    return this;
  };

  this.nth = function(n) {
    while(n-- > 0) this.next();
    return maps.reduce(this.next())(
      function(xs,y) { return y(xs); });
  };

  //'realize' elements
  this.take = function(n) {
    var tmpArr = [];
    while(n--) 
      tmpArr.push(maps.reduce(this.next())(
            function(xs,y) { return y(xs); })
          );
    return tmpArr;
  };
}