text: (function (tree) {
  
      tree.Paren = function (node) {
          this.value = node;
      };
      tree.Paren.prototype = {
          toCSS: function (env) {
              return '(' + this.value.toCSS(env) + ')';
          },
          eval: function (env) {
              return new (tree.Paren)(this.value.eval(env));
          }
      };
  
  })(require('../tree'));
  