Compiler warning using unicode package? · beginners

Hi. I'm completely new to Roc so apologies is this is a stupid question!
I'm working through some of the exercises on Exercism and I'm getting this warning on one of them:

── ● unreachable code ─ ../../../../.cache/roc/packages/4W8SHzvwet9hH9qZewJ1J1CVQoH7YKA6zyijWFTB3y1w/InternalGrapheme.roc:245:2

This code will never run, because the code before it always ends with a return, crash, or break, or loops forever.

Err(NoMore)
^^^^^^^^^^^

Remove this code, or change the code before it so that it can finish.

import unicode.Grapheme

MicroBlog :: {}.{
    truncate : Str -> Try(Str, _)
    truncate = |input| {
        grapheme_list = Grapheme.split(input).take_first(5)
        Ok(Str.join_with(grapheme_list, ""))
    }
}

Steve Howell (Oct 27 2026 at 12:07):

What roc build are you using? Can you post a snippet from the InternalGrapheme.roc (near line 245) for more context?

Oliver (Oct 27 2026 at 12:12):

Roc compiler version nightly-2026-10-21-5349569
The test code (in a separate file) is using:

app [] {
    unicode: "https://github.com/roc-lang/unicode/releases/download/4.2.0/4W8SHzvwet9hH9qZewJ1J1CVQoH7YKA6zyijWFTB3y1w.tar.zst",
}

next_range : RangeIterState -> Try((ByteRange, RangeIterState), [NoMore])
next_range = |state| {
    if state.finished {
        return Err(NoMore)
    }

But I don't know if that's the version of the package that the test code is using...

Steve Howell (Oct 27 2026 at 12:14):

next_range : RangeIterState -> Try((ByteRange, RangeIterState), [NoMore])
next_range = |state| {
    if state.finished {
        return Err(NoMore)
    }

    var $cursor = state.cursor
    var $machine = state.machine

    while Bool.True {
        match InternalUtf8.next($cursor) {
            Done => {
                if $machine.started {
                    range = ByteRange.from_bounds($machine.cluster_start, $cursor.byte_offset) ?? ...
                    return Ok((
                        range,
                        {
                            cursor: $cursor,
                            machine: $machine,
                            finished: Bool.True,
                        },
                    ))
                } else {
                    return Err(NoMore)
                }
            }
            One({ item, rest }) => {
                transition = InternalGrapheme.push($machine, item.scalar, item.byte_start)
                $cursor = rest
                $machine = transition.machine

                match transition.boundary {
                    NoBoundary => {}
                    Boundary({ start, end }) => {
                        range = ByteRange.from_bounds(start, end) ?? ...
                        return Ok((
                            range,
                            {
                                cursor: $cursor,
                                machine: $machine,
                                finished: Bool.False,
                            },
                        ))
                    }
                }
            }
        }
    }
}

Oliver (Oct 27 2026 at 12:14):

Steve Howell (Oct 27 2026 at 12:16):

Interesting! The error message definitely seems bogus, because finished is clearly a bool, so the conditional up top that Roc was whining about doesn't always fire.

RangeIterState : {
    cursor : InternalUtf8.Cursor,
    machine : MachineState,
    finished : Bool,
}

Oliver (Oct 27 2026 at 12:20):

I was using roc locally, rather than the Exercism browser version. Perhaps the test worked fine using the older version of the unicode package with whatever version of the compiler Exercism are using.
Anyway, using the latest version seems to work correctly so I guess it's not really a problem. Thanks for looking at it.

notramo (Oct 27 2026 at 12:25):

When I encounter compiler errors/warnings in official packages, it's nearly always a version incompatibility that goes away after I update the compiler to the latest nightly and the package to the latest released version.

Stream: beginners

Topic: Compiler warning using unicode package?

Oliver (Oct 27 2026 at 12:02):