Asbjørn Olling (Dec 01 2023 at 12:30): Asbjørn Olling (Dec 01 2023 at 12:30):This is not something that's stopping me in my tracks. Just something that feels like I'm holding it wrong.
How do you debug a roc function when it doesn't work as expected?
My usual go-to is calling the function from a repl, but I can't figure out how to import roc files from a repl.
The expect keyword is cool. But it doesn't tell me what the output actually was - just that it's wrong. (Not so useful)
The dbg keyword seems to be completely broken? It panics every time, so maybe it's just not implemented yet?
The only thing I can think of is turning everything into Task, and then doing the Num.toStr |> Stdout.line |> Task.await dance everytime.
...but it's a lot of cumbersome boilerplate and type-faffery just to get my eyes onto the result of a function call.
Am I doing it wrong?
How do I get to see the result of a function I wrote?
Ideally I'd like to just call my roc functions from a repl.
Is there something like python -i in Roc? Is it possible to import Roc code to the repl in any way?
Anton (Dec 01 2023 at 13:07):Importing roc files form the repl is not yet supported.
dbg should work a whole lot better now with today's nightly and basic-cli 0.7.0
Asbjørn Olling (Dec 01 2023 at 13:21):Hmm.. I'm on the very latest commit on roc master rn- and the compiler just panicks and says "this is definitely a compiler bug" whenever there is a dbg statement anywere. No matter where.
I'll try updating to basic-cli 0.7.0, and see if that makes a difference.
But I thought dbg was a language-specific thing, and not something implemented by the platform?
Richard Feldman (Dec 01 2023 at 13:23):we recently changed that - basically now the platform is in charge of specifying where dbg gets written to - so, for example, if you're running a WebAssembly platform in the browser, it might be implemented using console.log, or in a VS Code extension it might show up in a developer console
Richard Feldman (Dec 01 2023 at 13:23):but more relevantly here, the new way we're doing things fixes a bunch of bugs with the old implementation :big_smile:
Matthew Phillips (Dec 01 2023 at 13:25):I have noticed that the "this is definitely a compiler bug" message gets logged a lot, for things that are user errors
Asbjørn Olling (Dec 01 2023 at 13:27):dbg works once I've upgraded to basic-clli 0.7.0! yay thanks
Asbjørn Olling (Dec 01 2023 at 13:28):I'm guessing the error was just because I was using a too-old platform for a too-new version of roc.
Agus Zubiaga (Dec 01 2023 at 13:30):Matthew Phillips said:
I have noticed that the "this is definitely a compiler bug" message gets logged a lot, for things that are user errors
I think in some cases the bug is that there should be a better error message
Matthew Phillips (Dec 01 2023 at 13:32):Agus Zubiaga said:
Matthew Phillips said:
I have noticed that the "this is definitely a compiler bug" message gets logged a lot, for things that are user errors
I think in some cases the bug is that there should be a better error message
hah, fair point
Brendan Hansknecht (Dec 01 2023 at 15:17):Yeah, that error generally happens when somewhere in the compile we don't yet handle a case or assumed something is impossible.
Long term those should all either work or return pretty error message.
Johan Lindskogen (Dec 01 2023 at 16:25):I reported an issue the other day, noticed this thread, and upgraded the basic-cli but now I get what seems to be some macOS signing issue?
main: is already signed
I don't mean to press more on the issue, just added this here if it helps in any way :)
Anton (Dec 01 2023 at 16:27):Are you using today's nightly release?
Johan Lindskogen (Dec 01 2023 at 16:28):Anton said:
Are you using today's nightly release?
I recompiled latest main from source
Anton (Dec 01 2023 at 16:31):Strange, I'll try to reproduce
Anton (Dec 01 2023 at 16:45):Failed to reproduce on NixOS, will try on macOS
Luke Boswell (Dec 01 2023 at 17:20):Using expect works great for printing things out, if the test fails it prints the locally defined variables. So I like to do things like
expect
a = myfunc input
a == expectedValue
Here it will print out the value of a
Asbjørn Olling (Dec 02 2023 at 14:01):@Luke Boswell oooh I didn't realize you could do that. pretty dope!
Luke Boswell (Dec 02 2023 at 19:55):We could update the tutorial section to make this clearer by including the output for the example, and I think it would be helpful to mention it and link to the "tests and expectations" section in the "debugging" section
Asbjørn Olling (Dec 02 2023 at 20:00):For sure. I found myself a bit frustrated at not having exactly this ability - but then it was just in there! :sparkles:
timotree (Dec 07 2023 at 22:16):dbg just isn't printing anything for me with basic-cli 0.7.0. Am I doing something wrong?
app "dbg"
packages { pf: "https://github.com/roc-lang/basic-cli/releases/download/0.7.0/bkGby8jb0tmZYsy2hg1E_B2QrCgcSTxdUlHtETwm5m4.tar.br" }
imports [pf.Stdout, pf.Task.{ Task }]
provides [main] to pf
main : Task {} I32
main =
dbg "hello"
Stdout.line "world"
$ roc run dbg.roc
world
oh it's roc dev instead
timotree (Dec 07 2023 at 22:17):Is there a reason dbg is disabled for roc run? They both don't seem to use optimizations by default
Luke Boswell (Dec 07 2023 at 22:43):I agree, I've found this is a little confusing. I've started an idea discussion to maybe clarify what these mean.
Last updated: Jul 26 2025 at 12:14 UTC