Macro neis 

macro_rules! neis {
    ($h:expr, $( $x:expr ),* $(,)?) => { ... };
    ($h:expr) => { ... };
}

Like the crate::nes! macro, but for IndexSets.

use nonempty_collections::neis;

let s = neis![1, 2, 2, 3,];
assert_eq!(3, s.len().get());