[Openmcl-devel] GUI element needs

[Gary Byers]

On Mon, 8 Aug 2005, Hamilton Link wrote:

> Also maybe GB can at least remind us what the state of 
> the stepper is in openmcl (even if "absent").

It's absent, though it used to be present (and there was even a GTK
frontend for it, which almost certainly wouldn't work anymore.)

The old stepper depended on the old evaluator, which was suffering
severe bitrot.  I don't remember what the final straw was (maybe
some MOP things), but it didn't seem like it'd be maintainable any
longer.   In order to use the stepper, you had to either (a) turn
off CCL:*COMPILE-DEFINITIONS* before defining anything that you
wanted to step through of (b) save the lambda expressions along
with compiled functions and hope that macros/constants that were
in effect at compile-time were still around at "run evaluated under
the stepper" time.

The handwavy plan (for the last 15 years or so) has been to instrument
compiled code with

    (trap-if [stepping-enabled-in-current-thread])

sequences at strategic points and under either default or
slightly-oriented-towards-debugging optimization settings.  That's
a fair amount of work; you'd also want to map chunks of the source
lambda to those "strategic points" - I think that Alan Ruttenberg's
done some work on this in the past - and there are other issues.
I thought - and still think - that it'd be better to pursue the
idea of enabling stepping through compiled code than it would be
to try to keep a (rarely used and not always practical to use)
evaluator around.