[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.