Macro yarnspinner_core::yarn_fn_type

macro_rules! yarn_fn_type {
    (impl Fn($($param:ty),+) -> $ret:ty) => { ... };
}

A macro for using YarnFn as a return type or parameter type without needing to know the implementation details of the YarnFn trait.

This is useful when registering functions in a Library with Library::add_function.