Macro kaguya_rs::always

macro_rules! always {
    ($x:expr,$y:expr) => { ... };
    ($x:expr) => { ... };
    () => { ... };
    (=>) => { ... };
}

always return first memorized values

Syntax:

1. always!() :: a -> Any -> a
2. always!(=>) :: a -> (Any -> a)
3. always!(x) :: Any -> x
4. always!(x,_) = x