iter_mdo.rs

// Copyright (c) 2014 Guillaume Pinot <texitoi(a)texitoi.eu>
//
// This work is free. You can redistribute it and/or modify it under
// the terms of the Do What The Fuck You Want To Public License,
// Version 2, as published by Sam Hocevar. See the COPYING file for
// more details.

#[macro_use] extern crate mdo;

fn main() {
    // exporting the monadic functions for the Iterator monad (similar
    // to list comprehension)
    use mdo::iter::{bind, ret, mzero};

    // getting the list of (x, y, z) such that
    //  - 1 <= x <= y < z < 11
    //  - x^2 + y^2 == z^2
    let l = bind(1i32..11, move |z|
                 bind(1..z, move |x|
                      bind(x..z, move |y|
                           bind(if x * x + y * y == z * z { ret(()) }
                                else { mzero() },
                                move |_|
                                ret((x, y, z))
                                )))).collect::<Vec<_>>();
    println!("{:?}", l);

    // the same thing, using the mdo! macro
    let l = mdo! {
        z =<< 1i32..11;
        x =<< 1..z;
        y =<< x..z;
        when x * x + y * y == z * z;
        ret ret((x, y, z))
    }.collect::<Vec<_>>();
    println!("{:?}", l);
}