Re: Signals / Messages / Events / ...?

[Neil Jerram]

On 03/01/18 15:11, Christopher Howard wrote:
> On Wed, 2018-01-03 at 11:53 +0000, Neil Jerram wrote:
> > Well, one Lispy mechanism in that area is hooks.  For example, from
> > some
> > of my old code:
> >
> > ;; Changes to modem registration state are indicated by calling this
> > ;; hook with args STATE and PROPERTIES.  STATE can be 'none, meaning
> > ;; that there is currently no modem; 'unregistered, meaning that
> > there
> > ;; is a modem but it isn't registered with the network; or
> > ;; 'registered, meaning that the modem is registered with the
> > network.
> > ;; If STATE is 'registered, PROPERTIES is an alist of registration
> > ;; properties; otherwise PROPERTIES is #f.
> > (define registration-hook (make-hook 2))
> >
> > (define (add-registration-hook proc)
> >     (add-hook! registration-hook proc))
> >
> > (define (notify-registration state properties)
> >     (run-hook registration-hook state properties))
> >
> > Does that serve your purpose at all?
> >
> > Best wishes - Neil
> I think that should work. Only part I'm not sure about is if you can
> have a "one-off" procedure added to a hook... but you could just have
> the procedure call remove-hook! to remove itself...?

Yes, I think so, and you could encapsulate that with something like this:

(define (add-hook-once-only! hook proc)
  (letrec ((proc-once-only
            (lambda args
              (remove-hook! hook proc-once-only)
              (apply proc args))))
    (add-hook! hook proc-once-only)))

Best wishes - Neil