SWI-Prolog -- (initialization)/2

Availability:built-in

Similar to initialization/1, but allows for specifying when Goal is executed while loading the program text:

now: Execute Goal immediately.
after_load: Execute Goal after loading the program text in which the directive appears. This is the same as initialization/1.
prepare_state: Execute Goal as part of qsave_program/2. This hook can be used for example to eagerly execute initialization that is normally done lazily on first usage.
restore_state: Do not execute Goal while loading the program, but only when restoring a saved state.^{56Used
to be called restore. restore is still
accepted for backward compatibility.}
program: Execute Goal once after executing the -g goals at program startup. Registered goals are executed in the order encountered and a failure or exception causes the Prolog to exit with non-zero exit status. These goals are not executed if the -l is given to merely load files. In that case they may be executed explicitly using initialize/0. See also section 2.11.2.1.
main: When Prolog starts, the last goal registered using initialization(Goal, main) is executed as main goal. If Goal fails or raises an exception, the process terminates with non-zero exit code. If not explicitly specified using the -t the toplevel goal is set to halt/0, causing the process to exit with status 0. An explicitly specified toplevel is executed normally. This implies that -t prolog causes the application to start the normal interactive toplevel after completing Goal. See also the Prolog flag toplevel_goal and section 2.11.2.1.