roc/examples/cli/file.roc

app "file-io"
    packages { pf: "cli-platform/main.roc" }
    imports [
        pf.Program.{ Program, ExitCode },
        pf.Stdout,
        pf.Stderr,
        pf.Task.{ Task },
        pf.File,
        pf.Path,
        pf.Env,
        pf.Dir,
    ]
    provides [main] to pf

main : Program
main = Program.noArgs mainTask

mainTask : Task ExitCode [] [Write [File, Stdout, Stderr], Read [File, Env]]
mainTask =
    path = Path.fromStr "out.txt"
    task =
        cwd <- Env.cwd |> Task.await
        cwdStr = Path.display cwd

        _ <- Stdout.line "cwd: \(cwdStr)" |> Task.await
        dirEntries <- Dir.list cwd |> Task.await
        contentsStr = Str.joinWith (List.map dirEntries Path.display) "\n    "

        _ <- Stdout.line "Directory contents:\n    \(contentsStr)\n" |> Task.await
        _ <- Stdout.line "Writing a string to out.txt" |> Task.await
        _ <- File.writeUtf8 path "a string!" |> Task.await
        contents <- File.readUtf8 path |> Task.await
        Stdout.line "I read the file back. Its contents: \"\(contents)\""

    Task.attempt task \result ->
        when result is
            Ok {} ->
                Stdout.line "Successfully wrote a string to out.txt"
                |> Program.exit 0

            Err err ->
                msg =
                    when err is
                        FileWriteErr _ PermissionDenied -> "PermissionDenied"
                        FileWriteErr _ Unsupported -> "Unsupported"
                        FileWriteErr _ (Unrecognized _ other) -> other
                        FileReadErr _ _ -> "Error reading file"
                        _ -> "Uh oh, there was an error!"

                Stderr.line msg
                |> Program.exit 1