Coffeecript's list comprehension compilation.. crazy.

gistfile1.coffee

validate: (attrs, options) ->
    missing = [attr for attr in required if attrs[attr] is null]
    if missing.length > 0
        return "Missing #{missing.join(', ')}"

gistfile2.js

validate: function(attrs, options) {
    var attr, missing;
    return missing = [
      (function() {
        var _i, _len, _ref, _results;
        if (attrs[attr] === null) {
          _ref = ['project', 'ref', 'context'];
          _results = [];
          for (_i = 0, _len = _ref.length; _i < _len; _i++) {
            attr = _ref[_i];
            _results.push(attr);
          }
          return _results;
        }
      })()
    ];
}