off-side.rs

Build	Status
Travis-CI

Use off-side syntax (indent instead of braces, like in Python) to write Rust!

Disclaimer: implementing a different standard of the language is apparently not a good idea. This project is just a proof of concept for fun.

Off-side rule

Off-side rule means that a computer language uses indents instead of using {} braces to distinguish code hierarchy. Well-known examples include YAML (a data serialization language), Python (a programming language) and PugJS (a JavaScript markup preprocessor language).

Example

#[macro_use]
extern crate off_side;

use std::io::{Error, ErrorKind};

off_side! {

fn try_int(i: i32) -> Result<i32, Error>:
    match i:
        0 => Ok(1),
        1 => Err(Error::new(ErrorKind::NotFound, "Hello")),
        _ => unreachable!(),

fn main():
    for i in 0..2:
        let result = try_int(i);
        let num = match result:;
            Ok(i) => i,
            Err(err) => err.raw_os_error().unwrap_or_else(|| 3),
        println!("num: {}", num);

}

Syntax specification

• Indent rules follow the specification in the indent-stack crate.
• Due to proc_macro limitations, all indent characters are considered the same. In other words, if you mix tabs and spaces, tabs will be considered as one space.
• Do not place block comments /* */ before line start. They might be considered as spaces as well.
• On the parent line of indent blocks that should have been wrapped by braces, end the parent line with an extra :.
• If the braced indent block should be followed by a semicolon (e.g. let statements with match or if/else), end the parent line with :;.

Final disclaimer

This library is a proof of concept and just for fun. Not recommended for use in production or in publicly published crates.