Structured concurrency: fork-join

      f ( a, b, c, ...);

• In SJS function application, arguments a, b, c, ... are evaluated in parallel.
• The function body of f is evaluated when all arguments have finished evaluating.

      function fetch_some_feed() { ... }
      function fetch_another_feed() { ... }
      function wait_for_some_user_input() { ... }

      function do_something_with_feeds_and_users_input(a, b, c) { ... }

      do_something_with_feeds_and_users_input(
             fetch_some_feed(),
             fetch_another_feed(),
             wait_for_some_user_input()
      );