A simplest example

Let's start with what may be the simplest non-trivial timely dataflow program.

extern crate timely;

use timely::dataflow::operators::{ToStream, Inspect};

fn main() {
    timely::example(|scope| {
               .inspect(|x| println!("seen: {:?}", x));

This program gives us a bit of a flavor for what a timely dataflow program might look like, including a bit of what Rust looks like, without getting too bogged down in weird stream processing details. Not to worry; we will do that in just a moment!

If we run the program up above, we see it print out the numbers zero through nine.

    Echidnatron% cargo run --example simple
        Finished dev [unoptimized + debuginfo] target(s) in 0.05s
         Running `target/debug/examples/simple`
    seen: 0
    seen: 1
    seen: 2
    seen: 3
    seen: 4
    seen: 5
    seen: 6
    seen: 7
    seen: 8
    seen: 9

This isn't very different from a Rust program that would do this much more simply, namely the program

fn main() {
    (0..10).for_each(|x| println!("seen: {:?}", x));

Why would we want to make our life so complicated? The main reason is that we can make our program reactive, so that we can run it without knowing ahead of time the data we will use, and it will respond as we produce new data.