Re: Long-lived Guile scripts in a mono-threaded game engine

[Paul Emsley <paul.emsley@bioch.ox.ac.uk>]

Sylvain Beucler wrote:
> Hi,
>
> On Tue, May 27, 2008 at 09:58:46AM +0200, Ludovic Courtès wrote:
>   
>>> Scripts last more than a single game loop. They are not basic scripts
>>> that describe what happens in a single engine step; instead they
>>> describe what happens in the story.
>>>
>>> For example, a game introduction will create sprites on the screen,
>>> move them around, make them say lines that the user can read (or pass
>>> using [space]), etc.
>>>
>>> That script can also change the current screen (which kills all other
>>> scripts in the current script).
>>>
>>> Multiple scripts can run in a single screen, but they run the one
>>> after the other, not in parallel. The order/priority is known.
>>>
>>> Scripting is essentially frozen during the screen refresh. This avoids
>>> putting mutexes everywhere.
>>>
>>>
>>>
>>>
>>> How could I do something similar with Guile? I didn't find a way to
>>> make a guile script pause (and return to the caller).
>>>       
>> IIUC, "scripts" are only invoked via hooks, e.g., the engine wants to
>> ask them to do something specific.  If that is the case, it suffices to
>> not invoke the script.
>>
>> Surely you can implement coroutine-like behavior, either using `call/cc'
>> (but that is going to be prohibitively expensive), or using explicit
>> continuation-passing style or similar.  For instance, when a hook is
>> called by the engine, it would systematically return a thunk (a
>> zero-argument procedure) that the engine would later invoke.  Example:
>>
>>   (define (my-hook action)
>>     (let ((stuff (do-some-computation action)))
>>       (lambda ()
>>         ;; This will be executed at some later point, when the engine
>>         ;; feels like invoking it.
>>         (do-the-remaining-computation stuff))))
>>
>> Does this help?
>>     
>
> Ok, so what I'm looking for isn't supported natively :/
>
>
> Here's a sample script (very close to the C bindings, for a start):
>
> [snip script]
>
> Now every time we see a (say_stop), the script will pause for 2
> seconds, so the player can read the text.
>   

what is the nature of the pause? (I think that that might be 
important.)  How do you interrupt the tight little say_stop sleep loop 
(if that's what it is) when you are using C bindings?

> Maybe I'm missing a more simple solution?
>
>   

Maybe.