Macro rtforth::primitive

macro_rules! primitive {
    (fn $args:tt) => { ... };
    (fn $f:ident $args:tt $body:tt) => { ... };
    (fn $f:ident $args:tt -> isize $body:tt) => { ... };
    (fn $f:ident $args:tt -> &mut [usize; 2] $body:tt) => { ... };
}