1 unstable release

0.1.0 Feb 18, 2021

#166 in Command-line interface




A fast, extensible, command-line arguments parser.

Documentation ยท Tests

Introduction ๐Ÿ“š

The most popular argument parser, clap, allows you list all the possible arguments and their constraints, and then gives you a dynamic, stringly-typed object containing all the values. Usually these values are then manually extracted into structs and enums to access the values more conveniently and get the advantages of a static type system (example).

Parkour uses a different approach: Instead of parsing the arguments into an intermediate, stringly-typed object, it parses them directly into the types you want, so there's no cumbersome conversion. For types outside the standard library, you need to implement a trait, but in most cases this can be done with a simple derive macro.

This has several advantages:

  • It is very flexible: Every aspect of argument parsing can be tailored to your needs.
  • It is strongly typed: Many errors can be caught at compile time, so you waste less time debugging.
  • It is zero-cost: If you don't need a feature, you don't have to use it. Parkour should also be pretty fast, but don't take my word for it, benchmark it ๐Ÿ˜‰


Parkour started as an experiment and is very new (about 1 week old at the time of writing). Expect frequent breaking changes. If you like what you see, consider supporting this work by

  • Reading the docs
  • Trying it out
  • Giving feedback in this issue
  • Opening issues or sending PRs

Right now, parkour lacks some important features, which I intend to implement:

  • Auto-generated help messages
  • A DSL to write (sub)commands more ergonomically
  • More powerful derive macros
  • Error messages with ANSI colors


use parkour::prelude::*;

enum ColorMode {

struct Command {
    color_mode: ColorMode,
    file: String,

impl FromInput for Command {
    type Context = ();

    fn from_input<P: Parse>(input: &mut P, _: &Self::Context)
        -> Result<Self, parkour::Error> {
        // discard the first argument

        let mut file = None;
        let mut color_mode = None;

        while !input.is_empty() {
            if input.parse_long_flag("help") || input.parse_short_flag("h") {
                println!("Usage: run [-h,--help] [--color,-c auto|always|never] FILE");
                return Err(parkour::Error::early_exit());
            if SetOnce(&mut color_mode)
                .apply(input, &Flag::LongShort("color", "c").into())? {
            if SetPositional(&mut file).apply(input, &"FILE")? {

        Ok(Command {
            color_mode: color_mode.unwrap_or(ColorMode::Auto),
            file: file.ok_or_else(|| parkour::Error::missing_argument("FILE"))?,

Code of Conduct ๐Ÿค

Please be friendly and respectful to others. This should be a place where everyone can feel safe, therefore I intend to enforce the Rust code of conduct.


This project is licensed under either of

at your option.