. 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_info(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. Versions upto SWI-Prolog 8.5.2 defined this function as PL_version(). It was renamed to avoid a conflict with Perl affecting Yaswi. PL_version() is provided as a macro for 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 properties of all built-in predicates defined in C. If this function is called before PL_initialise() it returns 0.

12.4.21 Querying Prolog

long PL_query(int)

Obtain status information on the Prolog system. The actual argument type depends on the information required. int describes what information is wanted.^{231Returning pointers and integers as a long is bad style. The signature of this function should be changed.} The options are given in table 9.

PL_QUERY_ARGC	Return an integer holding the number of arguments given to Prolog from Unix.
PL_QUERY_ARGV	Return a char ** holding the argument vector given to Prolog from Unix.
PL_QUERY_SYMBOLFILE	Return a char * holding the current symbol file of the running process.
PL_MAX_INTEGER	Return a long, representing the maximal integer value represented by a Prolog integer.
PL_MIN_INTEGER	Return a long, representing the minimal integer value.
PL_QUERY_VERSION	Return a long, representing the version as 10,000 × M + 100 × m + p, where M is the major, m the minor version number and p the patch level. For example, 20717 means 2.7.17.
PL_QUERY_ENCODING