Brainf*ck in Rust (sort of, does not work)

bf.rs

struct tape { mem: ~[u8], ptr: uint }
pure fn tape() -> tape { tape { mem: vec::from_elem(10000u, 0u8), ptr: 0 } }

macro_rules! bf_rec(
    () => ();

    (+) => (tape.mem[tape.ptr] += 1u8);
    (-) => (tape.mem[tape.ptr] -= 1u8);
    (>) => (tape.ptr += 1u);
    (<) => (tape.ptr -= 1u);
    (.) => (io::stdout().write([tape.mem[tape.ptr]]));
    (,) => ({ let c = io::stdin().read_byte();
              if c >= 0 { tape.mem[tape.ptr] = c as u8; } });

    (<<) => (bf_rec!(< <));
    (>>) => (bf_rec!(> >));
    (->) => (bf_rec!(- >));
    (<-) => (bf_rec!(< -));
    (<->) => (bf_rec!(< - >));
    (..) => (bf_rec!(. .));

    ([ $($body)* ]) => (while tape.mem[tape.ptr] != 0u8 { bf_rec!($($body)*) });

    ($head:tt $($tail:tt)+) => ({ bf_rec!($head); bf_rec!($($tail)+); })
)

macro_rules! bf(
    () => ();
    ($($x:tt)*) => ({ let mut tape = tape(); bf_rec!($($x)*); })
)

fn main() {
    bf!(++++++++++++++++++++++++++++++++++++++++++..,.,.,.,.[.])
}