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 mik

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 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.