Macro pa::snd

macro_rules! snd {
    (>$($t:ty),*) => { ... };
    ($x:expr) => { ... };
    ($x:pat) => { ... };
}

Get the second element of tuple

Syntax:

1. snd!(>type,type…) :: (a,b,…) -> b
2. snd!((a,b,…)|) -> b
3. let x = (a,b); snd!(x) -> b