eager_lazy.js

Lazy = _.chain;

Lazy.range = function() {
  return _.chain(_.range.apply(_, arguments));
};

_.prototype.toArray = function() {
  return this.value();
};

var originalFlatten = _.prototype.flatten;
_.prototype.flatten = function() {
  var arr = this.map(function(x){
    return typeof x.value === 'function' ? x.value() : x;
  });
  return originalFlatten.call(arr);
}

var originalSortBy = _.prototype.sortBy;
_.prototype.sortBy = function(foo, reverse) {
  var arr = originalSortBy.call(this, foo);
  return reverse ? arr.reverse() : arr;
}

_.prototype.sum = function(foo) {
  return this.reduce(function(memo, num) {
    return memo + (typeof foo === 'function' ? foo(num) : num);
  }, 0).value();
};

_.prototype.chunk = function(size) {
  return _.chain(this.reduce(function(memo, num) {
    if (memo.length === 0) {
      return [[num]];
    } else {
      var lastArr = memo[memo.length - 1];
      if (lastArr.length < size) {
        lastArr.push(num);
      } else {
        memo.push([num]);
      }
    }
    return memo;
  }, []));
};

_([ 'find', 'some', 'every' ]).each(function(foo) {
  var original = _.prototype[foo];
  _.prototype[foo] = function() {
    return original.apply(this, arguments).value();
  };
});