code: func ObjectOperand(x ast.Value, pos int) (ast.Object, error) {
  	o, ok := x.(ast.Object)
  	if !ok {
  		return nil, NewOperandTypeErr(pos, x, "object")
  	}
  	return o, nil
  }
docs: // ObjectOperand converts x to an object. If the cast fails, a descriptive
  // error is returned.