code: function parseArrayInitialiser() {
          var elements = [];
  
          expect('[');
  
          while (!match(']')) {
              if (match(',')) {
                  lex();
                  elements.push(null);
              } else {
                  elements.push(parseExpression());
  
                  if (!match(']')) {
                      expect(',');
                  }
              }
          }
  
          expect(']');
  
          return delegate.createArrayExpression(elements);
      }
docs: 11.1.4 Array Initialiser