SWI-Prolog -- library(debug)

assertion/1	Acts similar to C assert() macro.
assertion_failed/2	This hook is called if the Goal of assertion/1 fails.
debug/1	Add/remove a topic from being printed.
debug/3	Format a message if debug topic is enabled.
debug_message_context/1	Specify additional context for debug messages.
debug_print_hook/3	Hook called by debug/3.
debugging/1	Examine debug topics.
debugging/2	Examine debug topics.
list_debug_topics/0	List currently known topics for debug/3 and their setting.
list_debug_topics/1	List currently known topics for debug/3 and their setting.
nodebug/1	Add/remove a topic from being printed.