2023 day 2 · roctoberfest · Zulip Chat Archive

Made use of the |> List.mapTry \r -> r

Tim Wise (Oct 02 2023 at 13:42):

Very easy to follow the compiler errors, even without any IDE help. I did get briefly confused by the references to the desugared operator names in error messages eg. doing Ok a + b makes it complain about arguments to the add function.

Anton (Oct 02 2023 at 14:20):

Thanks for your feedback @Tim Wise, I made #5878 for the add function issue.

Elias Mulhall (Oct 03 2023 at 04:53):

https://github.com/mulias/roctoberfest/blob/main/advent_2022/day_02/main.roc
This time I used @Luke Boswell's parser library and used crash to report errors early when they didn't seem important to solving the puzzle.

Elias Mulhall (Oct 03 2023 at 04:54):

I also thought that this error message was nice, really easy to tell what was wrong

── TYPE MISMATCH ──────────────────────────────────────────────────── main.roc ─

The branches of this when expression don't match the condition:

58│>      when (playerHand, opponentHand) is
59│           (Rock, Rock) -> Draw
60│           (Rock, Paper) -> Loss
61│           (Rock, Scissors) -> Win
62│           (Paper, Rock) -> Win
63│           (Paper, Paper) -> Draw
64│           (Paper, Scissors) -> Loss
65│           (Scissors, Rock) -> Loss
66│           (Scissors, Paper) -> Win
67│           (Scissors, Scissor) -> Draw

The when condition is a tuple of type:

    (
        Shape,
        Shape,
    )a

But the branch patterns have type:

    (
        [
            Paper,
            Rock,
            Scissors,
        ],
        [
            Paper,
            Rock,
            Scissor,
            Scissors,
        ],
    )a

The branches must be cases of the when condition's type!

Luke Boswell (Oct 03 2023 at 04:59):

Did you see the URL package? you should be able to use lukewilliamboswell/roc-parser by including the url in module header like this

app "example"
    packages {
        cli: "https://github.com/roc-lang/basic-cli/releases/download/0.5.0/Cufzl36_SnJ4QbOoEmiJ5dIpUxBvdB3NEySvuH82Wio.tar.br",
        parser: "https://github.com/lukewilliamboswell/roc-parser/releases/download/0.1.0/vPU-UZbWGIXsAfcJvAnmU3t3SWlHoG_GauZpqzJiBKA.tar.br",
    }
    imports [

Luke Boswell (Oct 03 2023 at 05:02):

ooh, actually I think I may have removed whitespace... I can add that back in.

Elias Mulhall (Oct 03 2023 at 05:04):

Yea that was the issue, I just updated and copied in the missing whitespace parser

Last updated: Jul 26 2025 at 12:14 UTC

Stream: roctoberfest

Topic: 2023 day 2

Tim Wise (Oct 02 2023 at 13:35):