This library provides tools to control the Prolog debuggers.
Traditionally this code was built-in. Because these tools are only
required in (interactive) debugging sessions they have been moved into
the library.
- [multifile]prolog:debug_control_hook(+Action)
- Allow user-hooks in the Prolog debugger interaction. See the calls below
for the provided hooks. We use a single predicate with action argument
to avoid an uncontrolled poliferation of hooks.
- [det]spy(:Spec)
- [det]nospy(:Spec)
- [det]nospyall
- Set/clear spy-points. A successfully set or cleared spy-point is
reported using print_message/2,
level
informational, with one of the following terms, where Spec
is of the form M:Head.
- See also
- spy/1 and nospy/1
call the hook prolog:debug_control_hook/1
to allow for alternative specifications of the thing to debug.
- [det]debugging
- Report current status of the debugger.
- [multifile]debugging_hook
- Multifile hook that is called as
forall(debugging_hook, true)
and that may be used to extend the information printed from other
debugging libraries.
- [det]trap(+Formal)
- [det]notrap(+Formal)
- Install a trap on
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
- det
- 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
debugger.
- Edit exceptions menu in PceEmacs and the graphical debugger
that provide a graphical frontend to trap exceptions.
- [multifile]trap_alias(+Alias,
-Error)
- Define short hands for commonly used exceptions.
