15 - Procedures and Functions

Abstract

Procedures and functions are the building blocks of all but the simplest programs. Deciding the method to break the different parts of a complex program into components is one of the most difficult aspects of software development. This chapter covers the basic mechanics of the way to use procedures and functions. It touches only briefly on the more difficult problem of the way to organize the procedures and functions into a working program. This chapter covers the basics of writing and using procedures and functions. The essential points about Interactive Data Language (IDL) programming modules are: Variables are local to the procedure or function that contains them unless they are included in the argument list. Arguments in the argument list are matched according to the order in the list in the calling procedure and the called procedure. Keyword parameters can be given in any order and even mixed with positional parameters. Within a procedure or function, the keyword name should generally be the same as the local variable it is associated with (for example, PRINT = print). The capitalization simply emphasizes that there is a keyword tag PRINT.