std/args

import "std/args"

Cli cli = new_cli("greet", "Greets someone")
set_version(cli, "1.0")
add_flag(cli, "loud", "l", "Shout the greeting")
add_option(cli, "name", "n", "NAME", "Who to greet", "world")
add_color_option(cli)
Args a = parse_args(cli, args())

str greeting = "Hello, " + option(a, "name")
if flag(a, "loud") then
    greeting = upper(greeting)
end
print(greeting)

greet --help then prints:

greet 1.0 - Greets someone

Usage: greet [options]

Options:
  -l, --loud          Shout the greeting
  -n, --name <NAME>   Who to greet (default: world)
      --color <WHEN>  Use colors: auto, always, or never (default: auto)
  -h, --help          Show this help
  -V, --version       Show the version

Function	Does
`new_cli(name, about)`	starts a description of the program's arguments
`set_version(cli, version)`	adds `-V` and `--version`
`add_flag(cli, name, short, help)`	a flag such as `--loud` or `-l`; `short` may be `""`
`add_option(cli, name, short, value_name, help, fallback)`	an option with a value, or `fallback` when it is not given
`add_command(cli, name, help)`	a subcommand: the first positional argument must be one
`add_positional(cli, name, help)`	describes a positional argument in the help
`set_rest_count(cli, min, max)`	limits the positional arguments; `max` -1 for any number
`add_color_option(cli)`	adds `--color auto/always/never`, applied by `parse_args`
`parse_args(cli, argv)`	parses `args()`; prints help, the version, or an error and exits when needed
`try_parse_args(cli, argv)`	the same as a `Result`, without printing or exiting
`flag(a, name)`	whether a flag was given
`option(a, name)`	an option's value, or its fallback
`option_int(a, name)`	the value as a `Result[int]`
`given(a, name)`	whether an option was given at all
`help_text(cli)`	the help as `--help` prints it
`apply_color(a)`	applies `--color` from `add_color_option`, as `parse_args` does after `try_parse_args`
`edit_distance(a, b)`	how many one-character edits turn `a` into `b`
`did_you_mean(word, choices, prefix)`	`" (did you mean '--name'?)"` for the closest choice, with `prefix` before it, or `""` when none is close

Args holds command, the subcommand or "", and rest, the positional arguments. Options can be written --name value, --name=value, -n value, or -nvalue, short flags can be grouped as -lv, and -- ends the options. Errors come with a suggestion when one is close, such as unknown option '--verbos' (did you mean '--verbose'?), and end the program with status 2.