Subdivided procedures: a language extension supporting extensible programming

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 RPDE/sup 3/ 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.<>