Graph Procedure Composition

Great! Now Graph Procedures have given us free concurrency just by structuring our code declaratively rather than imperatively. But as we'd realistically only want to put a few nodes in a single Graph Procedure from a code maintenance and readability point of view, how do we write DAGS that are larger than just a few nodes? Composition! By this I mean simply calling another Graph Procedure from within the current one.

For Example:

graph function bar(argB: ..., argC: ...) -> future<...> {
    root barRes <- doBar(@b1);
    node b1 <- doBar1(@b2, @b3);
    node b2 <- doBar2(argB);
    node b3 <- doBar3(argC);
graph function foo(argA: ...) → future<...> {
    root fooRes <- doFoo(@f1, @f2);
    node f1 <- doFoo1(@f3);
    node f2 <- bar(10, @f3); # <-- Graph Composition via Call to `bar`.
    node f3 <- doFoo3(argA);

Because foo(...) includes a call to bar(...) as a subgraph, you can imagine that node f2 in graph foo actually composes around the entire bar graph.

This composition is extremely simple to understand in this way. The entire subgraph is started after all data dependencies of the node wrapping it are ready.