:- use_module(library(prolog_debug)).(can be autoloaded)
error(Formal, Context)exceptions that unify. The tracer is started when a matching exception is raised. This predicate enables debug mode using debug/0 to get more context about the exception. Even with debug mode disabled exceptions are still trapped and thus one may call nodebug/0 to run in normal mode after installing a trap. Exceptions are trapped in any thread. Debug mode is only enabled in the calling thread. To enable debug mode in all threads use tdebug/0.
Calling debugging/0 lists the enabled traps. The predicate notrap/1 removes matching (unifying) traps.
In many cases debugging an exception that is caught is as simple as below (assuming run/0 starts your program).
?- trap(_). ?- run.
The multifile hook trap_alias/2 allow for defining short hands for commonly used traps. Currently this defines
- Trap determinism exceptions raised as a result of the det/1 directive.
- Trap rule existence error exceptions.
- See also
- - gtrap/1 to trap using the graphical
- Edit exceptions menu in PceEmacs and the graphical debugger that provide a graphical frontend to trap exceptions.