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

[Neil Jerram <neil@ossau.homelinux.net>]

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