A programmer controlled approach to data and control abstraction

Traditionally, data abstraction languages have only provided a means to extend the language “upward” to include new procedures and data types not present in the base language. This paper introduces a complementary approach, which also allows programmers to extend the language “downward” and thus to override many of the previously preempted decisions concerning the nature and implementation of various language constructs. In order to illustrate the approach, several extension examples are presented that involve control of decisions below the level of Pascal-like languages. Implementation of the programmer defined language constructs is also discussed and benchmark results are reported that show them comparable—and in many cases exceeding—in efficiency the corresponding built-in constructs of conventional languages.