Stream: beginners

Topic: ✔ OS-specific APIs in platforms

Richard Feldman (Oct 08 2026 at 18:02):

I have some ideas about how to handle this but I haven't figured out the right way yet

Richard Feldman (Oct 08 2026 at 18:06):

one idea is:

• have a builtin effectful function called like System.target! which returns some system info
• included in the system info would be a tag union for which OS you have, and each tag would have a payload consisting of a different opaque type (e.g. `Linux :: {}) and there would be no other way to obtain an instance of these opaque types besides this tag union
• now platforms can have functions that take a Linux argument, which means you can only call them if you got one of those values from the tag union, which in turn means you're running on Linux

Richard Feldman (Oct 08 2026 at 18:10):

the reason I'd do it as an effectful function (System.target!) is that we currently have the invariant that if you call a Roc pure function passing the same arguments, you are guaranteed to get the same answer no matter what target you're building for. I wouldn't want to sacrifice that invariant just to make this operation callable in more places, especially when the reason you'd use it would be to unlock calling effectful functions from your platform anyway.

Richard Feldman (Oct 08 2026 at 18:11):

but of course if it's going to be an effectful function, it doesn't need to be a builtin; any platform can just offer an effectful function like that today

Richard Feldman (Oct 08 2026 at 18:12):

or, alternatively, pass the target info into main! along with env etc. - that has the downside that application authors would need to thread it through more places, but there are other tradeoffs to doing it that way.

Richard Feldman (Oct 08 2026 at 18:13):

anyway, so I don't know whether it will someday make sense to do that as a builtin, but certainly for right now there's nothing stopping any platform from doing that today, so that's what I'd recommend!

Richard Feldman (Oct 08 2026 at 18:14):

happy to explain any of the details there

notramo (Oct 08 2026 at 23:31):

Thanks, this seems to be a good solution without changing the language.

notramo (Oct 08 2026 at 23:32):

I agree with the platform check function being effectful.

Notification Bot (Oct 08 2026 at 23:33):

notramo has marked this topic as resolved.

Last updated: Oct 15 2026 at 17:56 UTC