What is this thing?

What is this thing?

The PL/I preprocessor is a general-purpose macro processor. It was designed to add macro capability to the PL/I language, but in fact has the ability to operate on nearly any text data (exceptions noted below). The PL/I preprocessor includes functionality similar to the C preprocessor, but is much more powerful, including looping and branching absent from C.

The preprocessor is not part of the PL/I language standard, but many compilers include a version similar to IBM’s, perhaps with some differences.