Hook for the debugger control predicates that allows the creator of more
high-level programming languages to use the common front-end predicates
to control the debugger. For example, XPCE uses these hooks to allow for
spying methods rather than predicates. Action is one of:
Hook in spy/1.
If the hook succeeds spy/1
takes no further action.
Hook in nospy/1.
If the hook succeeds nospy/1
takes no further action. If spy/1
is hooked, it is advised to place a complementary hook for
Hook in nospyall/0.
Should remove all spy points. This hook is called in a failure-driven
Hook in debugging/0.
It can be used in two ways. It can report the status of the additional
debug points controlled by the above hooks and fail to let the system
report the others, or it succeeds, overruling the entire behaviour of debugging/0.