Stream: ideas

Topic: main type signature

view this post on Zulip Anton (May 10 2025 at 13:07):

I think we should include the type signature of main! in most cases (like on the examples repo). Type mismatches for beginners will be less confusing if they can see the type of main!. It does come at the cost of brevity but I think it's worth it.
Before:

app [main!] { cli: platform "https://github.com/roc-lang/basic-cli/releases/download/0.19.0/Hj-J_zxz7V9YurCSTFcFdu6cQJie4guzsPMUi5kBYUk.tar.br" }

import cli.Stdout

main! = |_args|
    Stdout.line!("Hello, World!")

After:

app [main!] { cli: platform "https://github.com/roc-lang/basic-cli/releases/download/0.19.0/Hj-J_zxz7V9YurCSTFcFdu6cQJie4guzsPMUi5kBYUk.tar.br" }

import cli.Stdout
import pf.Arg exposing [Arg]

main! : List Arg => Result {} _
main! = |_args|
    Stdout.line!("Hello, World!")

view this post on Zulip Richard Feldman (May 10 2025 at 13:53):

for absolute beginners, it's super important to me to teach types only after teaching how to build things

view this post on Zulip Richard Feldman (May 10 2025 at 13:53):

like how it's done in e.g. Python

view this post on Zulip Anton (May 10 2025 at 13:58):

I agree with that for lessons and the tutorial etc. but if they're trying stuff on their own, starting from hello world, they will hit a type mismatch fast once they start altering main!.

view this post on Zulip Brendan Hansknecht (May 10 2025 at 14:04):

Examples likely should be what we consider solid, but beginner friendly code. I think that means a type for every top level function

view this post on Zulip Brendan Hansknecht (May 10 2025 at 14:05):

I do agree for first learning, types should be 100% avoided.

view this post on Zulip Richard Feldman (May 10 2025 at 14:36):

that's fair, for examples outside tutorials

Last updated: Jun 16 2026 at 16:19 UTC