y a‘]’and a newline. Then start the tracer. format and the arguments are the same as for printf(2). Always returns FALSE.

12.4.18 Environment Control from Foreign Code

int PL_action(int, ...)

Perform some action on the Prolog system. int describes the action. Remaining arguments depend on 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

Write the argument, a char * to the current output stream.

PL_ACTION_FLUSH

Flush the current output stream. Requires no arguments.

PL_ACTION_ATTACH_CONSOLE

Attach a console to a thread if it does not have one. See attach_console/0.

PL_GMP_SET_ALLOC_FUNCTIONS

Takes an integer argument. If TRUE, the GMP allocations are immediately bound to the Prolog functions. If FALSE, SWI-Prolog will never rebind the GMP allocation functions. See mp_set_memory_functions() in the GMP documentation. The action returns FALSE if there is no GMP support or GMP is already initialised.

unsigned int PL_version(int key)

Query version information. This function may be called before PL_initialise(). If the key is unknown the function returns 0. See section 2.22 for a more in-depth discussion on binary compatibility. Defined keys are:

PL_VERSION_SYSTEM

SWI-Prolog version as 10,000 × major + 100 × minor + patch.

PL_VERSION_FLI

Incremented if the foreign interface defined in this chapter changes in a way that breaks backward compatibility.

PL_VERSION_REC

Incremented if the binary representation of terms as used by PL_record_external() and fast_write/2 changes.

PL_VERSION_QLF

Incremented if the QLF file format changes.

PL_VERSION_QLF_LOAD

Represents the oldest loadable QLF file format version.

PL_VERSION_VM

A hash that represents the VM instructions and their arguments.

PL_VERSION_BUILT_IN

A hash that represents the names, arities and prop