Safely Extending Procedure Types to Allow Nested Procedures as Values

摘要

The concept of nested procedure values, i.e., the possibility of using nested procedures as values of procedure types, is a useful and powerful concept. Nevertheless, it is not allowed in languages such as Modula-2 and Oberon(-2), because it creates a serious security hole when used inappropriately. To prevent such misuse while at the same time retaining the benefits of the concept, alternative language rules as well as a small language extension for Oberon-2 are suggested, which allow nested procedures to be safely used as values of procedure types and especially to pass them as parameters to other procedures.