Signals in Scheme

Here’s the translation of the Go code to Scheme, formatted in Markdown suitable for Hugo:

Our program demonstrates handling Unix signals in Scheme. It shows how to gracefully handle signals like SIGTERM or SIGINT. Here’s the implementation:

(import (chicken process-context)
        (chicken process-signal))

(define (main)
  ; Create a channel to receive signal notifications
  (define sigs (make-channel))

  ; Register the channel to receive SIGINT and SIGTERM signals
  (set-signal-handler! signal/int
    (lambda () (channel-send sigs 'SIGINT)))
  (set-signal-handler! signal/term
    (lambda () (channel-send sigs 'SIGTERM)))

  ; Create a channel to notify when the program should exit
  (define done (make-channel))

  ; Start a separate thread to handle signals
  (thread-start!
   (lambda ()
     (let ((sig (channel-receive sigs)))
       (newline)
       (print sig)
       (channel-send done #t))))

  ; Wait for the signal
  (print "awaiting signal")
  (channel-receive done)
  (print "exiting"))

(main)

In this Scheme implementation:

1. We import necessary modules for process context and signal handling.

2. We define a main function that encapsulates our program logic.

3. We create a channel sigs to receive signal notifications.

4. We use set-signal-handler! to register handlers for SIGINT and SIGTERM. These handlers send the respective signals to the sigs channel.

5. We create a done channel to notify when the program should exit.

6. We start a separate thread (analogous to a goroutine) that waits for a signal on the sigs channel. When it receives a signal, it prints it and sends a message on the done channel.

7. The main thread prints “awaiting signal” and then waits for a message on the done channel.

8. Once a signal is received and processed, the program prints “exiting” and terminates.

To run this program:

$ csc signals.scm
$ ./signals
awaiting signal
^C
SIGINT
exiting

When we run this program, it blocks waiting for a signal. By typing ctrl-C (which the terminal shows as ^C), we can send a SIGINT signal, causing the program to print SIGINT and then exit.

Note that Scheme implementations may vary, and this example uses CHICKEN Scheme. The exact syntax and available libraries might differ in other Scheme implementations.