8.1. Overview of functions in SAA The functionality of the interface is divided into some main areas: · Subcommand handlers which trap and handle a command to an external environment. · External function handlers extend the REXX language with external functions · Interpreting REXX scripts, either from a disk file, or from memory. · Variable interface which makes it possible to access the variables in the interpreter, and allows operations like setting, fetching and dropping variables. · System exits which are used to hook into certain key points in the interpreter while it executes a script. In the following sections each of these areas are described in detail, and a number of brief but complete examples are given at the end of the chapter. The description is of a highly technical nature, since it is assumed that the reader will be an application programmer seeking information about the interface. Therefore, much of the content is given as prototypes and C style datatype definitions. Although this format is cryptic for non-C programmers, it will convey exact, compact, and complete information to the intended readers. Also, the problems with ambiguity and incompleteness that often accompany a descriptive prose text are avoided.