Re: Watchpoints for emacs lisp.

[Stefan Monnier]

> In GDB there are watchpoints to stop when changing the value, but there are
> also watchpoints to stop when read/write.

> It should be done here the same.

I don't know about "should".  There are different kinds of watchpoint
you might be interested in, and there are different techniques you can
use to implement a watchpoint feature.  Depending on the technique you
use, that restricts the kind of watchpoints you can support.

Using a field on the `symbol' structure only allows you to catch
modifications via setq/let (and friends).  It's very limited, but has
the advantage of being very simple, cheap, and lightweight to implement.

If you want to be able to watch a random expression (which would be
great, of course), then indeed you'll need something a lot more
intrusive, such as a playing MMU tricks or adding extra checks at
various places.


        Stefan