Stream: beginners

Topic: Example that hangs the roc type checker (but only locally)

cerk (Aug 06 2026 at 22:55):

Just messing around with Roc again and I wrote this incorrect code:

main! = |_args| {
    a = ["Larry", "Curly", "Moe"]
    b = a.swap(0, 2)
    echo!("${Str.inspect(b.get(0))}\n")
    Ok({})
}

Since b is of type Try, it doesn't make sense to call get on it. When I attempt to run this program with Roc, it appears to enter an infinite loop during type checking. However, if I run this code on the Roc website, it responds with the correct error: This get method is being called on a value whose type doesn't have that method.

Roc compiler version nightly-2026-08-06-61bbb59

I'm not confident enough to know if this needs reporting or not since it works on the website.

Thanks for reading!

Luke Boswell (Aug 06 2026 at 23:04):

Sounds like a bug if its in an infinite loop, a GH issue would be appreciated :smile:

cerk (Aug 06 2026 at 23:12):

Ok, here it is:

#10654

Last updated: Aug 12 2026 at 12:35 UTC