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

[Neil Jerram]

On 03/01/18 05:09, Christopher Howard wrote:
> Hi list, forgive me if this is a somewhat vague question... but is
> there some kind of framework/system/approach for Guile where you could
> have different parts of your code register callback functions to react
> to a certain signal or message raised by any other part of the code?
> I'm thinking like dbus where I guess you can sort of send off a message
> but not really care who receives it. In chickadee you can register
> callbacks for the various input events, and i think that basic idea
> could be extended so long as (1) you could have any kind of
> event/signal you wanted; (2) call backs added could be specified as
> either persistent or one-time call-backs.
>
> It seems like it wouldn't be too hard to code something like that with
> just lists of callback functions tied to names/data in a tree. But
> maybe somebody has already thought of that or would suggest a better
> approach.
>
> Just running into this challenge in development where a function like
> "new-game" has to do 8 different things to 6 different data structures,
> but why not instead just have the code dealing with the 6 different
> objects register callbacks to receive the 'new-game signal? I think
> message passing is the wrong term because in message passing you
> specify the message connections between the different objects, right?
> Signal bus maybe?

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