✔ basic-cli Opt/Param docs · beginners

Actually, maybe one more question. Is there a pattern for non-empty list in either basic-cli or weaver? I ended up using Opt.strList and a followup custom logic:

    when Cli.parseOrDisplayMessage cli args is
        Ok input ->
            if List.isEmpty input.versions then
                Stderr.line! "No versions to benchmark"
                Task.err (Exit 1 "")
            else
                Bench.run input

        Err message ->
            Stderr.line! message
            Task.err (Exit 1 "")

Martin Janiczek (Oct 02 2024 at 08:29):

I guess if there's no Opt.nonemptyStrList my best option is to extract the above length check into some validateInput function that I use with Result.try?

Martin Janiczek (Oct 02 2024 at 08:30):

as in, when args |> Cli.parseOrDisplayMessage cli |> Result.try validateInput is ...

Sam Mohr (Oct 02 2024 at 08:47):

@Martin Janiczek I'd say you have a couple options:

First is to ask for two fields, the first being a single value and the second being a list:

cliParser =
    { Cli.weave <-
        file: Param.str { name: "file", help: "The file to process." },
        files: Param.strList { name: "files", help: "The rest of the files." },
    }

parsed = parseArgsWith! cliParser args

allFiles = List.concat [file] files

Second is to validate the list value, which still requires post-parsing handling:

cliParser =
    { Cli.weave <-
        # other fields...
        files: Param.strList { name: "files" }
            |> Cli.map \fs -> if List.isEmpty fs then Err EmptyFiles else Ok fs
    }

parsed = parseArgsWith! cliParser args

files = parsed.files?

Last updated: Jul 26 2025 at 12:14 UTC