Hacker News Reader

Comment by schemescape | Hacker News Reader

Last I checked, Lua was “bring your own debugger”. Assuming that hasn’t changed, a REPL is nice, but you can’t pause and inspect anything by default.

View on HN

To be the most fair, Fennel 1.4 recently released with an `assert-repl` form that opens a repl when some assertion fails, in which you can inspect local variables, etc. That's getting closer to CL.

https://git.sr.ht/~technomancy/fennel/tree/1.4.0/item/change...

Thanks for the correction! I had only used Lua, and thought Fennel had no runtime, so I assumed this was not possible.

Fennel has a form `assert-repl` which will drop into the REPL wherever, if the condition fails. For writing games you can launch the REPL in the game loop if a keyboard button is pressed. But what you can't do, that I know of, is interrupt arbitrary execution and get a Fennel REPL. You'd probably need a lua debugger of some sort for that. I'm not that familiar with that though.

Why can't you just put the equivalent of `(repl)` wherever you want to debug and drop into your REPL?

Short answer: I don’t know. That sounds like a good idea, but how would that access local variables in the caller (to inspect state)?

I remember the Lua C API exposes a lot of information, but I didn’t think it was accessible from scripts. Of course, it was a long time ago and I could have easily missed something at the time. Happy to be corrected!

Edit: you might also run into difficulties trying to redefine non-global functions to add the call to “repl”.

Reply on news.ycombinator.com