Programming with PV-WAVE
The routines discussed in this chapter are characterized by the fact that they are useful primarily (though not exclusively) in PV-WAVE procedures and functions. They are rarely used during interactive use. They provide information about variables and expressions, give the programmer control over how errors are handled, and perform other useful operations.
Routines may be loosely categorized into the following groups:
Error handling routines such as ON_ERROR, ON_IOERROR, FINITE, and CHECK_MATH. Informational routines which return information about variables, expressions, parameters, etc. These routines are N_ELEMENTS, SIZE, N_PARAMS, PARAM_PRESENT, and KEYWORD_SET. In addition, TAG_NAMES and N_TAGS supply information about structure variables. Program control routines such as EXIT, EXECUTE, STOP, and WAIT. 
