[Lispweb] debugging and serving web pages at the same time in lisp (specifically clisp)

Richard Newman r.newman at reading.ac.uk
Thu Oct 5 17:58:16 CDT 2006

On  5 Oct 2006, at 11:11 PM, Yin-So Chen wrote:

> Thanks Ivan, Richard, and Lawrence for responding - this is all  
> very intriguing.  Sounds like CGI is the only sure way to go with  
> Clisp if I am looking to run multiple concurrent sessions?

Depends. If you're limited to clisp, perhaps.

> Also - Lawrence, I am assuming you have a way to capture your  
> changes in life system back into source code form easily?  I've  
> heard the save-image capability, but would think you still need to  
> have source code so you can rebuild image again if you can, is this  
> correct?

Generally, you make changes in the source, then evaluate your changes  
in the REPL. If you're lucky, things will work out :)

> Richard - you meant you can (trace) h-r-r in SBCL, right?  In  
> CLISP, once (host-serve-events) is called, it blocks REPL, so I  
> can't do trace just-in-time without killing off the lisp session (I  
> can't tell whether there is a way to accept a control-character  
> within araneida).

Hmm. On SBCL serve-event does not block the REPL; I don't use clisp.

> BTW Ivan - I did find a blog article by BillClementson discussing  
> the same topic at http://bc.tech.coop/blog/040224.html.
> Based on all the descriptions so far, I am wondering if the  
> development "methodology" is completely different with lisp.

Yes, it is.

> I so far lived in the compile-link-install-test world, where most  
> of syntactic bugs and some semantic bugs are caught during the  
> compile phase. And that leaves the bugs that are harder to find in  
> live systems.  Of course, examining trace files is horrible  
> compared to live traces, but I've found that a good majority of the  
> bugs found in production requires non-trivial changes (even with  
> decent abstraction layers) and hence my experience is that without  
> going through another test cycle, changing is extremely risky.

You verify things on a test server, if you can, or by local testing  
of some kind... then make the change in the running server without a  

> Unless... there is a way to quickly verify and rollback changes  
> easily in lisp?

Do it locally.

> It would be great if someone with experiences in both worlds (I am  
> sure many of you do ;p) can share some light on whether lisp's  
> development cycle is completely different than c/c++/java/c#  
> world.  I've started to write lisp code, but my limited experience  
> does not allow me to grok this yet.

Yes, it is. You don't ever need to restart, unless you're testing  
startup code! I've had systems which I've maintained, running, for 6  
months; I keep the source up to date on-disk, and they've shut down  
and restarted without any difficulties.

You're also not limited to a compile-run-test-edit cycle to find out  
if you're right; you can work with live data in a REPL, so you're  
much more likely to be right, and you don't ever have the shutdown/ 
restart delay.


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