[kbp]

Not quite. In Lisp, when you get an error, the system pauses and lets you resolve the issue before resuming the program. Sometimes this even means typing in a function really quickly before a request times out (which isn't such an insane suggestion in the context of development). In Clojure, errors like that unwind the stack and tear everything down.

[vram22]

Reminds me of Paul Graham's essay about how at Viaweb, they sometimes used to fix bugs (in the Lisp code) while the customers who reported them were still on the phone, and then the support staff would tell them to check whether they were sure it was a bug, by trying again - and since the bug was now fixed in the server, when they did that operation again, it would work.

I think it was in his Beating the Averages essay - the one in which he talks a lot about the advantages Lisp gave them at Viaweb, over the competition.

[krapp]

You could do that with a PHP site if you're working directly in production. That's not necessarily an advantage of Lisp.

[vram22]

I think I had not described it fully (since had read it long ago). Searched for the article just now. The Beating the Averages article [1] does not have the point I mentioned. But a more detailed article [2] linked from it, does:

[1] http://paulgraham.com/avg.html

[2] More Technical Details: http://paulgraham.com/lwba.html (note: redirects twice)

Here's the relevant section:

[ Interactive Toplevel

Lisp's interactive toplevel is a great help in developing software rapidly. But the biggest advantage for us was probably in finding bugs. As I mentioned before, with Web-based applications you have the users' data on your servers and can usually reproduce bugs.

When one of the customer support people came to me with a report of a bug in the editor, I would load the code into the Lisp interpreter and log into the user's account. If I was able to reproduce the bug I'd get an actual break loop, telling me exactly what was going wrong. Often I could fix the code and release a fix right away. And when I say right away, I mean while the user was still on the phone.

Such fast turnaround on bug fixes put us into an impossibly tempting position. If we could catch and fix a bug while the user was still on the phone, it was very tempting for us to give the user the impression that they were imagining it. And so we sometimes (to their delight) had the customer support people tell the user to just try logging in again and see if they still had the problem. And of course when the user logged back in they'd get the newly released version of the software with the bug fixed, and everything would work fine. I realize this was a bit sneaky of us, but it was also a lot of fun. ]

[vram22]

So it was the interactive toplevel and the break loop [1] that seem to have provided the advantage.

[1] Discussed in this same thread, e.g. this comment by mikelevins:

https://news.ycombinator.com/item?id=14677016

Not sure if PHP has that.

Incidentally, I seem to remember the following: some years ago, after playing around some with Lisp (Allegro CL from Franz, and the Lisp IDE from Lispworks, both of which supported this feature or something like it), I was trying out a then-current version of Visual Studio, and saw that it had a new feature called Edit-and-Continue, which I thought was similar to the Lisp feature.

[vram22]

Good point, see my other comment though.