Stream: beginners

Topic: Could main! allow any error to be returned?

Aurélien Geron (Jul 29 2026 at 22:28):

In the old Roc compiler, I liked the fact that the main! function could return any error, and it would just be printed out. Now every error has to be mapped to Exit(U32). This is arguably a good thing for production software, but for dev and quick scripts, I find it a bit cumbersome. Perhaps there could be an option to enable the old behavior, for example: roc --dev foo.roc?

Bryce Miller (Jul 29 2026 at 22:37):

Hmm, I thought this was up to the platform author. It looks like basic-CLI is still wired up to do this but I haven’t tested it recently so I could be wrong.

Aurélien Geron (Jul 29 2026 at 22:39):

Oh thanks, I didn't know it was up to the platform author, that makes sense. So I guess that's a question for @Luke Boswell ?

Bryce Miller (Jul 29 2026 at 22:39):

I'm actually about to do some other stuff with basic-cli so I could test it while I'm at it

Aurélien Geron (Jul 29 2026 at 22:43):

Btw, the basic CLI platform used to provide Utc.now!, Utc.to_nanos_since_epoch, and Sleep.millis!. It would be great to add these back if possible.

Aurélien Geron (Jul 29 2026 at 22:44):

And maybe Http.send! as well?

Bryce Miller (Jul 29 2026 at 22:54):

I'm testing with v0.21.0 released 2 days ago, and it appears that it allows arbitrary errors like you want. If you return an error other than Exit(I32) it prints a message and then just does Str.inspect on whatever error you returned.

Aurélien Geron (Jul 29 2026 at 22:55):

Oh great, I didn't know 0.21.0 was released, I'll try it out now.

Bryce Miller (Jul 29 2026 at 22:55):

Yeah I just noticed the new release myself :sweat_smile:
Looks like it also has Utc.now!

Bryce Miller (Jul 29 2026 at 22:56):

At a minimum the Tcp api changed a bit, not sure what else.

Aurélien Geron (Jul 29 2026 at 22:57):

Wowowowow

Luke Boswell (Jul 29 2026 at 22:57):

Yeah I thought it had sleep and those other functions. Ive got work things on today and cant really look at it closely.

Richard Feldman (Jul 29 2026 at 23:05):

Aurélien Geron said:

In the old Roc compiler, I liked the fact that the main! function could return any error, and it would just be printed out. Now every error has to be mapped to Exit(U32). This is arguably a good thing for production software, but for dev and quick scripts, I find it a bit cumbersome. Perhaps there could be an option to enable the old behavior, for example: roc --dev foo.roc?

I'd like to go back to that old design. So the return type of main! becomes Try({}, Exit(I32), ..) and then the platform does a match on that Try with other => crash "The CLI crashed with:\n\n${other.inspect()}"

The nice thing about it is if you want the current API, it's trivial to get - just have main! call a function with that narrower signature and you're all set.

Bryce Miller (Jul 29 2026 at 23:13):

It looks like that is the way basic-cli is working currently, except that instead of crashing with a message it's logging to stderr and exiting with 1

Richard Feldman (Jul 30 2026 at 00:19):

that also works!

Last updated: Aug 12 2026 at 12:35 UTC