STSDAS applications are written in SPP, or Subset PreProcessor, which is the native programming language of the IRAF system. SPP is based on RATFOR--rational Fortran--and combines the familiarity of Fortran with some features of the C programming language. Users who wish to write applications that access the full range of IRAF capabilities should really learn and use SPP rather than the IMFORT or F77VOS interfaces. The greatest advantage of SPP is its portability. Applications written in SPP that use the data I/O and other interfaces correctly, can most likely be compiled and installed, without modification, on any machine and operating system for which an IRAF port exists.
The SPP Programmer's Reference, which is available from the STSDAS group, is a reasonably complete guide to writing and implementing SPP applications. This guide covers the basics of the language syntax, the system libraries and interfaces, and error handling. The guide also provides example procedures, instructions on compiling and linking programs as IRAF tasks, and instructions for debugging and maintaining tasks once they are written.