Subdivided procedures: A language extension supporting extensible programming

Abstract

An extension of conventional procedures in which procedure bodies handling multiple cases can be subdivided into separate bodies handling a single case each is described. Subdivision is based on criteria specified by the programmer. Underlying call support selects the body to execute in response to each call. Subdivided procedures support a programming style in which great attention is paid to facilitating subsequent extensions. Normally, extensions have to be made by changing source code; subdivided procedures allow them to be made instead by adding new bodies. Subdivided procedures can be implemented on top of procedural languages with a preprocessor that examines just a file of definitions; it does not need to examine procedure code. A restricted version of the mechanism implemented within the RPDE3 environment framework has been in constant use for more than two years. Experience has shown that it facilitates extensible programming at little or no cost in call-time overhead.