Roc projects structure · beginners

Stream: beginners

Can someone please correct my understanding of existing project types in Roc (if it's wrong) and how to reuse code.

Platforms are more or less clear, we have examples
Apps too. Every app has to have a platform to execute on. main.roc is an entrypoint.
Module is a more general thing - just a file exposing types or terms.

So far so good.

Interfaces. Are they still a thing? And if yes - what are they? I couldn't find any docs, but see them from time to time (e.g. in roc-datetime)
Packages are supposed to be reusable libs and don't have an associated platform. And that's the only things I could figure out about them. The rest are the questions:

What is the correct way to write a header? I see at least two options: roc-html and roc-parser
How do I use a 3rd-party package from my package? I see some examples for apps, but not for packages. I tried package [Foo] { html: "https://github.com/Hasnep/roc-html/[something].tar.br" }, but if I import anything in html the build just hangs (compiler is getting several BuildTasks, last of them being Solve, then getting stuck in load_single_threaded loop, although load_multi_threaded seems to be busier)
It seems to be a bug in compiler that I'm about to debug and report, but I'm curious if I'm doing anything wrong.
Different packages have different folder structure. Is it correct that it doesn't matter as long as final tar.br has main.roc?

Interfaces. Are they still a thing?

interface has been renamed to module

What is the correct way to write a header? I see at least two options: roc-html and roc-parser

Like in roc-html is the most up to date way to do it

Thanks! At least I was doing all the right way. I guess it means I just stumbled upon a bug in a compiler

I'll take a look

Yes, that issue still reproduces and is likely what is causing your problem too, I've changed it's priority to high

Thanks again! I'll post some more info there

Last updated: Nov 09 2025 at 12:14 UTC