Trampoline implementation in Rust

trampoline.rs

#![feature(unboxed_closures)]

fn main() {
    let x = from_str::<int>(std::os::args()[1].as_slice()).unwrap();
    let n = Bounce::Incomplete(x).execute(|n| {
        match n {
            n if n < 1 => Bounce::Fault("Value out of range."),
            1i => Bounce::Complete(n),
            n  => Bounce::Incomplete(n - 1i),
        }
    });

    println!("{}", n);
}

enum Bounce<R> {
    Incomplete(R),
    Complete(R),
    Fault(&'static str),
}

impl<R> Bounce<R> {
    fn execute(mut self, f: |R| -> Bounce<R>) -> R {
        loop {
            match self {
                Bounce::Incomplete(value) => { self = f(value); },
                Bounce::Complete(value) => { return value; },
                Bounce::Fault(message) => { panic!(message); },
            }
        }
    }
}