Concurrency

spawn starts a native thread task; join waits for its result. The closure and result must satisfy Send. fork-task instead uses the work-stealing pool; fib.parallel adds scopes, ordered maps and reductions. async is the stackless tier, driven by block-on; these tiers have different scheduling costs. Use an Atom for shared updates, and a private Cell for local ones. Next: deployment.

(ns main)
(defun main () -> i64
  (let ((task (spawn (fn () (+ 20 22)))))
    (do (println (join task)) 0)))

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