Macro union_async_spawn 

macro_rules! union_async_spawn {
    ($($proc_macro:tt)*) => { ... };
}

Use to spawn ::tokio::spawn per each step of each branch.

#![recursion_limit="512"]

extern crate union;
extern crate futures;
extern crate tokio;

use union::union_async_spawn;
use futures::future::ok;

#[tokio::main]
async fn main() {
    let product = union_async_spawn! {
        ok::<_,u8>(2u16) |> |v| Ok::<_,u8>(v.unwrap() + 2u16) ?> |_| {
            println!("Hello from parallel world!");
            // !!! Don't use std::thread::sleep to wait inside future because it will block executor thread !!!
            // It's used here only to show that futures are executed on multi thread executor.
            ::std::thread::sleep(::std::time::Duration::from_secs(1));
            println!("I'm done.");
        },
        ok::<_,u8>(3u16) ?> |_| {
            println!("Hello from parallel world again!");
            // !!! Don't use std::thread::sleep to wait inside future because it will block executor thread !!!
            // It's used here only to show that futures are executed on multi thread executor.
            ::std::thread::sleep(::std::time::Duration::from_secs(2));
            println!("Me too.");
        },
        ok::<_,u8>(4u16),
        map => |a, b, c| a * b * c
    }.await.unwrap();

    assert_eq!(product, 48);
}