CLI apps

args() is the argument list. std/args reads flags and options from it, and std/cli builds the whole command from a record type.

Reading arguments

std/args takes a token list. cli() takes the real arguments; cliOf(list) takes a list you supply, which is how a test checks the parsing without a process.

flag asks whether a token is present. opt reads --name=value and --name value, and answers Option<String>. positionals returns what is left, and rest returns what follows --.

site/guide/cliargs.vyrnBuilt

// `std/args` reads a token list. `cli()` takes the real arguments; `cliOf` takes
// a list you hand it, which is what a test does.
import { cliOf, flag, opt, positionals } from "std/args"
import { joinWith } from "std/strings"

export fn demo() -> String {
    let a = cliOf(["--verbose", "--port=8080", "site", "docs"])
    let port = match opt(a, "--port") {
        Some(v) => v,
        None => "none",
    }
    let short = flag(a, "-v")
    let long = flag(a, "--verbose")
    let rest = joinWith(positionals(a), ", ")

    return joinWith([
        "-v          \{short}",
        "--verbose   \{long}",
        "port        \{port}",
        "positionals \{rest}",
    ], "\n")
}

fn main() -> Int64 {
    print(demo())
    return 0
}

// `std/args` reads a token list. `cli()` takes the real arguments; `cliOf` takes
// a list you hand it, which is what a test does.
import { cliOf, flag, opt, positionals } from "std/args"
import { joinWith } from "std/strings"

export fn demo() -> String {
    let a = cliOf(["--verbose", "--port=8080", "site", "docs"])
    let port = match opt(a, "--port") {
        Some(v) => v,
        None => "none",
    }
    let short = flag(a, "-v")
    let long = flag(a, "--verbose")
    let rest = joinWith(positionals(a), ", ")

    return joinWith([
        "-v          \{short}",
        "--verbose   \{long}",
        "port        \{port}",
        "positionals \{rest}",
    ], "\n")
}

fn main() -> Int64 {
    print(demo())
    return 0
}

-v false --verbose true port 8080 positionals site, docs

std/cli

std/cli goes further. Declare a record whose fields are the options, and give each field a validated type with its own documentation line. cli("./module") reflects it into a parser and a help text, so no flag name is written twice.

A parse answers Valid or Invalid with the issues attached to their fields, so a program reports every problem at once instead of the first one.