Crate defmac

A macro to define lambda-like macros inline.

Syntax:

defmac!( name [ pattern [, pattern … ]] => expression )

name is the name of the new macro, followed by 0 or more patterns separated by comma. A pattern can be just an argument name like x or a pattern like ref value, (x, y) etc. Note that there is no comma between the name and the first pattern.

Example

#[macro_use] extern crate defmac;

fn main() {
    defmac!(mkvec iter => iter.into_iter().collect::<Vec<_>>());

    let v = mkvec!((0..10).map(|x| x * 2));

    defmac!(repeat ref s, n => (0..n).map(|_| &s[..]).collect::<String>());

    let text = String::from("abc");
    let s = repeat!(text, 10);
    let t = repeat!("-", s.len());
    println!("{}", s);
    println!("{}", t);

}

Did you know that macros can “capture” variables that they have in scope? The capture is by name instead of by reference, so we can use defmac where we cannot use closures. See the example below:

#[macro_use] extern crate defmac;

fn main() {
    let mut result = Vec::new();
    let mut sum = 0.;
    let input = "2 2 ^ 7 b ^";

    defmac!(push elem => result.push(elem));
    defmac!(double => *result.last_mut().unwrap() *= 2);

    for ch in input.chars() {
        match ch {
            '^' => double!(),
            '0'...'9' => push!(ch as u32 - '0' as u32),
            'a'...'z' => push!(ch as u32 - 'a' as u32),
            _ => { }
        }
    }

    assert_eq!(
        result,
        vec![2, 4, 7, 2]);
}

Rust Version

This crate requires Rust 1.20 or later.

Macros

• defmac
  A macro to define lambda-like macros inline.