HPlogo System Debug Reference Manual > Chapter 2 User Interface

Control-Y

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System Debug allows the user to prematurely terminate command execution by entering a Control-Y (press and hold the CONTROL key and press Y). Command loops, display loops and modification loops can be interrupted with this mechanism.

When Control-Y is entered during window updates, interrupted output lines may disturb portions of the windows. When this occurs, redraw the windows with the RED (redraw) command.

NOTE: There is only one Control-Y handler per session. When Debug is entered, it takes ownership of the Control-Y handler. When Debug is exited, it returns the Control-Y handler to the process that owned it when Debug was entered.

If other processes are active in a session while Debug is being used, it is possible for one of the other process to steal Control-Y ownership from Debug. In this situation, when Debug exits it will, in effect, steal Control-Y back from the current owner and give it to the process that owned it when Debug was entered. If Control-Y is stolen from Debug, it is also possible to create infinite loops in Debug from which there is no way out (for example, "while TRUE do {}").

Both DAT and Debug rearm the Control-Y trap after every CI command (for example, the ":" command).



Error Handling

Command History, REDO