cond! and switch! macros for Rust

macros.md

Scheme-style cond

macro_rules! cond(
    ($($pred:expr => $body:block),+ _ => $default:block) => (
        $(if $pred $body else)+
        
        $default
    )
)

fn main() {
    let x = 102;
    cond!(
        x < 100 => { io::println(~"woops"); },
        x > 300 => { io::println(~"hullo"); }
        _       => { io::println(~"bananas"); }
    )
}

C-style switch

Rust's match statement can't handle the use of variables and constants from parent scopes because it conflicts with pattern matching. The alternative is to use lots of ifs and elses:

fn key_to_str(key: int) -> ~str {
    // If we tried using 'match' here we'd get an error for each sub-statement:
    // `error: pattern variable conflicts with a constant in scope`
    if      key == GLFW_KEY_0 { ~"0" }
    else if key == GLFW_KEY_1 { ~"1" }
    else if key == GLFW_KEY_2 { ~"2" }
    else if key == GLFW_KEY_3 { ~"3" }
    else if key == GLFW_KEY_4 { ~"4" }
    else if key == GLFW_KEY_5 { ~"5" }
    else if key == GLFW_KEY_6 { ~"6" }
    else if key == GLFW_KEY_7 { ~"7" }
    else if key == GLFW_KEY_8 { ~"8" }
    else if key == GLFW_KEY_9 { ~"9" }
    else { fail(~"Unsupported key."); }
}

Here's a switch macro to help:

macro_rules! switch(
    ($var:expr { $($pred:expr => $body:block),+ _ => $default:block }) => (
        $(if $var == $pred $body else)+
        
        $default
    )
)

fn key_to_str(key: int) -> ~str {
    switch!(key {
        GLFW_KEY_0  => { ~"0" },
        GLFW_KEY_1  => { ~"1" },
        GLFW_KEY_2  => { ~"2" },
        GLFW_KEY_3  => { ~"3" },
        GLFW_KEY_4  => { ~"4" },
        GLFW_KEY_5  => { ~"5" },
        GLFW_KEY_6  => { ~"6" },
        GLFW_KEY_7  => { ~"7" },
        GLFW_KEY_8  => { ~"8" },
        GLFW_KEY_9  => { ~"9" }
        _           => { fail(~"Unsupported key."); }
    })
}

Rust has changed a lot since you wrote this, you might want to update it to not confuse newcomers to the language