Tickers in Scheme

Our example demonstrates how to use tickers for periodic tasks. In Scheme, we’ll use the (sleep) function to simulate tickers, as Scheme doesn’t have a built-in ticker mechanism like some other languages.

(import (chicken time))
(import (chicken format))

(define (run-ticker)
  (let ((start-time (current-seconds)))
    (let loop ((tick-count 0))
      (if (< tick-count 3)
          (begin
            (sleep 0.5)
            (printf "Tick at ~A~%" (seconds->string (current-seconds)))
            (loop (+ tick-count 1)))
          (printf "Ticker stopped~%")))))

(define (main)
  (run-ticker))

(main)

In this Scheme implementation:

1. We import the necessary modules: (chicken time) for time-related functions and (chicken format) for formatted output.

2. We define a run-ticker function that simulates the behavior of a ticker:

   • It runs for 3 ticks (equivalent to the 1600ms in the original example).
   • Each tick is separated by a 0.5-second sleep (500ms).
   • We print the current time for each tick.

3. The main function simply calls run-ticker.

4. Finally, we call the main function to start the program.

To run this program, save it as tickers.scm and execute it using your Scheme interpreter. For example, if you’re using CHICKEN Scheme:

$ csc tickers.scm
$ ./tickers
Tick at 2023-06-10T12:34:56Z
Tick at 2023-06-10T12:34:57Z
Tick at 2023-06-10T12:34:57Z
Ticker stopped

This implementation mimics the behavior of the original example, printing the time at each tick and stopping after 3 ticks. Note that Scheme doesn’t have built-in concurrency primitives like channels or goroutines, so we’ve simplified the example to run sequentially.

The concept of tickers is useful when you want to perform actions at regular intervals. In real-world applications, you might use this pattern for tasks like updating a user interface, checking for new data, or performing periodic maintenance operations.