macro_rules! define_callbacks { ( $($(#[$attr:meta])* [$($modifiers:tt)*] fn $name:ident($($K:tt)*) -> $V:ty,)*) => { ... }; }
macro_rules! define_callbacks { ( $($(#[$attr:meta])* [$($modifiers:tt)*] fn $name:ident($($K:tt)*) -> $V:ty,)*) => { ... }; }