n the requested action. The actions are listed below:

PL_ACTION_TRACE

Start Prolog tracer (trace/0). Requires no arguments.

PL_ACTION_DEBUG

Switch on Prolog debug mode (debug/0). Requires no arguments.

PL_ACTION_BACKTRACE

Print backtrace on current output stream. The argument (an int) is the number of frames printed.

PL_ACTION_HALT

Halt Prolog execution. This action should be called rather than Unix exit() to give Prolog the opportunity to clean up. This call does not return. The argument (an int) is the exit code. See halt/1.

PL_ACTION_ABORT

Generate a Prolog abort (abort/0). This call does not return. Requires no arguments.

PL_ACTION_BREAK

Create a standard Prolog break environment (break/0). Returns after the user types the end-of-file character. Requires no arguments.

PL_ACTION_GUIAPP

Windows: Used to indicate to the kernel that the application is a GUI application if the argument is not 0, and a console application if the argument is 0. If a fatal error occurs, the system uses a windows messagebox to report this on a GUI application, and otherwise simply prints the error and exits.

PL_ACTION_TRADITIONAL

Same effect as using --traditional. Must be called before PL_initialise().

PL_ACTION_WRITE