Macro dyon::dyon_fn

macro_rules! dyon_fn {
    (fn $name:ident () -> $rt:ty $b:block) => { ... };
    (fn $name:ident ($($arg:tt : $t:ty),+) -> $rt:ty $b:block) => { ... };
    (fn $name:ident () $b:block) => { ... };
    (fn $name:ident ($($arg:tt : $t:ty),+) $b:block) => { ... };
}