Re: handling state the database way

On 02/18/2014 10:36 AM, Paulo Moura wrote:
> The design idea behind the "single_fact" module centralizes (for an
> application) the handling of mutable data.  This can be both an
> advantage (a single place to hold the mutable data) and a
> disadvantage (multiple modules using this module must be careful to
> use different keys). This makes "single_fact" more like a *prototype*
> solution than an ideal *library* solution. As a library solution it
> comes with a bias towards a single central, global store.
> 
> Logtalk provides a bit more flexible library solution by using a
> category instead. A Logtalk category is a fine-grined unit of code
> reuse that can be (virtually) imported by any object. Using the
> "single_fact" module suggested predicates, we can define:

Logtalk's abstracting has a cleaner design than classical Prolog
modules, but that doesn't mean we can't realise module local
storage with Prolog modules:

:- meta_predicate
	initialize(:, +),
	...

initialize(Module:Key, Value) :-
	asserta(Module:store(Key, Value)).

...

And the central store is just

	initialize(central:size, 42).

	Cheers --- Jan