4.5.3 Extra Condition in Regina Regina has some other extra conditions. These conditions are: · A condition DEBUG, that is very similar to the condition HALT. The condition is raised as a result of an event of external origin, generally a special combination of keystrokes is pressed. · The default-action of this condition is to set the trace mode to Normal and interactive. Consequently, the user will generally get into interactive tracing at the next clause boundary. This way, the user may be able to stop the program during execution, and perform debugging. · The delay-action of this condition is to ignore it. · On Unix machines, this is the signal QUIT (SIGQUIT), which is normally bound the <ctrl>-\ key. Just like condition HALT, this might also be simulated from the command line, or from other programs. Consult the Unix documentation for more information. On VAX/VMS machines, this event is normally bound to the <ctrl>-<y> key. · This extended condition will only be available if the extension COND_DEBUG has been chosen. Whether or not the conditions listed here are available, may also depend on whether particular preprocessor flag was set during compilation. For more information, see the chapter on extensions.