macro sadness

gistfile1.rs

#[feature(macro_rules)];

// Shorthand for state-machine actions.
macro_rules! one (
    ( inc   ) => ( self.counter += 1; );
    ( print ) => ( println!("counter is {:d}", self.counter); );
)

// A DSL for sequencing shorthand actions.
macro_rules! go (
    ( $a:tt ; $($rest:tt)* ) => ({ one!($a); go!($($rest)*); });
    ( $($cmd:tt)+ ) => ( one!($($cmd)+); );
    () => (());
)

// Conditional action.
macro_rules! match_counter ( ( 0 ( $($eq0:tt)+ ) else ( $($ne0:tt)+ ) ) => (
    match self.counter {
        0 => go!($($eq0)+),
        _ => go!($($ne0)+),
    }
))

struct Machine {
    counter: int,
}

impl Machine {
    fn run(&mut self) {
        go!(inc; inc; print);
        // works

        match_counter!(
            0    (inc)
            else (print)
        );
        // foo.rs:31:22: 31:23 error: Local ambiguity: multiple parsing options: built-in NTs tt ('eq0') or 1 other options.
        // foo.rs:31             0    (inc)
        //                                ^
    }
}

fn main() {
    let mut m = Machine { counter: 0 };
    m.run();
}