code: function() {
      var node = this.logical();
      if (this.accept('?')) {
        var trueExpr = this.expression();
        this.expect(':');
        var falseExpr = this.expression();
        node = new nodes.Ternary(node, trueExpr, falseExpr);
      }
      return node;
    }
docs: logical ('?' expression ':' expression)?