Displaying a backtrace?

[Bill Gribble]

For debugging purposes I want to be able to print a backtrace in a
(catch) handler while continuing to run... basically
false-if-exception except printing a backtrace in addition to
returning false.

However, I can't ascertain how to print out a backtrace from within my
catch handler.  (backtrace) displays the message "No backtrace
available", even if I have explicitly done (debug-enable 'backtrace).
(display-backtrace (fluid-ref the-last-stack) (current-output-port))
prints nothing.  I'm just guessing that the-last-stack is the stack I
want to print.

Any thoughts? 

Thanks,
Bill Gribble