Stream: beginners

Topic: Getting unhandled parse error

view this post on Zulip Andres Villegas (Dec 08 2022 at 23:47):

Hi! I am giving roc a try with the day1 of advent of code. I wanted to do a sort of "Hello World" and come up with the following code 

app "day1"
    packages { pf: "https://github.com/roc-lang/basic-cli/releases/download/0.1.1/zAoiC9xtQPHywYk350_b7ust04BmWLW00sjb9ZPtSQk.tar.br" }
    imports [pf.Stdout, pf.Task.{ Task }, pf.File, pf.Path,]
    provides [main] to pf

parse = \strs ->
    List.map strs (\str -> Int.fromStr str)

main =
    path = "d1p1.txt"
    task =
        lines <- File.readUtf8 path |> Task.await
        parsed = parse (Str.split lines "\n")
        Stdout.line "Hello"

    Task.attempt task \res ->
        when res is
            Ok {} -> dbg "Ok"
            Err err ->  dbg err

I am aware some of the functions might not exists like Str.split or Int.fromStr I was just trying out stuff and see which functions might exists or not. Instead I am getting a Rust panic 

thread 'main' panicked at 'not yet implemented: unhandled parse error: Dbg(Continuation(IndentEnd(@542), @542), @534)', crates/reporting/src/error/parse.rs:576:14
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

If I move code around the panic goes away but it still doesn't compile, and I get errors like the following

 9│  main =
10│      path = "d1p1.txt"
11│      task =
12│          lines <- File.readUtf8 path |> Task.await
13│          parsed = parse (Str.split lines "\n")
                                                  ^

This definition is missing a final expression. A nested definition
must be followed by either another definition, or an expression

    x = 4
    y = 2

    x + y%

Is it an indentation error? I am missing some return value from main? Thanks for the language and for the help!

view this post on Zulip Brendan Hansknecht (Dec 08 2022 at 23:51):

Can you post the full reordered code that gives you the second error?

view this post on Zulip Brendan Hansknecht (Dec 08 2022 at 23:54):

Oh, actually i think i see the problem.

I think it is the use of the dbg keyword. It doesn't return anything. It just prints a value. So i think that is confusing the compiler. Main is expected to evaluate to a task that can't error (errors need to be handled in main). So you would need to return a final task.

view this post on Zulip Brendan Hansknecht (Dec 08 2022 at 23:58):

What if you change your attempt lambda to something like:

when res is
    Ok {} ->
        dbg "Ok"
        Task.succeed {}
    Err err ->
        dbg err
        Task.succeed {}

view this post on Zulip Andres Villegas (Dec 09 2022 at 00:08):

Thanks! I think it worked. I though that main needed to return something but I was not sure what it was

Last updated: Jul 26 2025 at 12:14 UTC