Channel Directions in Lisp

(defpackage :channel-directions
  (:use :cl))

(in-package :channel-directions)

;; This `ping` function only accepts a channel for sending
;; values. It would be a compile-time error to try to
;; receive on this channel.
(defun ping (pings msg)
  (send-channel pings msg))

;; The `pong` function accepts one channel for receives
;; (`pings`) and a second for sends (`pongs`).
(defun pong (pings pongs)
  (let ((msg (receive-channel pings)))
    (send-channel pongs msg)))

(defun main ()
  (let ((pings (make-channel :buffer-size 1))
        (pongs (make-channel :buffer-size 1)))
    (ping pings "passed message")
    (pong pings pongs)
    (format t "~A~%" (receive-channel pongs))))

When using channels as function parameters in Lisp, you can specify if a channel is meant to only send or receive values. This specificity increases the type-safety of the program.

In this example, we’re using a hypothetical channel library for Lisp. The actual implementation may vary depending on the specific Lisp dialect and concurrent programming library you’re using.

The ping function only accepts a channel for sending values. It would be a compile-time error to try to receive on this channel.

The pong function accepts one channel for receives (pings) and a second for sends (pongs).

In the main function, we create two channels with a buffer size of 1. We then call ping to send a message, pong to receive and resend the message, and finally print the received message.

To run this program, you would typically load it into your Lisp environment and call the main function:

(main)

This would output:

passed message

Note that the exact syntax and functions for channel operations (make-channel, send-channel, receive-channel) may differ based on the specific concurrent programming library you’re using in Lisp. This example assumes a library with similar semantics to Go’s channels.