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;; https://www.investopedia.com/articles/active-trading/101014/basics-algorithmic-trading-concepts-and-examples.asp
(define-trade-algo
  (given (moving-average (stock "USD/gold")
                         (duration (days 200))))
  (let ((short-term-trend (moving-average (stock "USD/gold")
                                          (duration (days 50))))
        (long-term-trend (moving-average (stock "USD/gold")
                                         (duration (days 200))))
        (significant-difference 0.1))
    (cond
     ((> (- short-term-trend long-term-trend) significant-difference)
      (buy (stock "USD/gold") 50))
     ((< (- short-term-trend long-term-trend) significant-difference)
      (sell (stock "USD/gold") 50)))))

;; might expand into the following asynchronous callback code

(begin
  (let ((queue (obtain-queue!)))
    (exchange-orders
     (lambda (exchange)
       (let ((command (dequeue! queue)))
         (case command
           ((buy) (fix! exchange 'buy "USD/gold" 50))
           ((sell) (fix! exchange 'sell "USD/gold" 50))))))
    (monitor-stock
     (lambda (backlog)
       (let ((short-term-trend (moving-average backlog (* 50 duration/days)))
             (long-term-trend (moving-average backlog (* 200 duration/days)))
             (significant-difference 0.1))
         (cond
          ((> (- short-term-trend long-term-trend) significant-difference)
           (enqueue! queue 'buy))
          ((< (- short-term-trend long-term-trend) significant-difference)
           (enqueue! queue 'sell))))))))