Re: Interactive programming with pengines

Hi Torbjörn,

Having something like that seems great for understanding pengine
interaction. The downside is that except for learning to play with them,
I see no use for this. Right? If right, I'm a bit reluctant to add
complications to the code only for demo and playing purposes.

After all, the idea behind pengines is the same as behind Paul Tarau's
engines: have a _machine_ interact with Prolog engines. (except that
Paul's engines are local and aiming at Prolog only interaction where
yours are either local or remote and aim also at interacting with other
languages). We already have the toplevel for interacting with users.

Wouldn't it make more sense to write a web application that allows for
playing with the pengine protocol? That opens the playground for people
that may be less experienced using Prolog.

	Cheers --- Jan

P.s.	At some point I'd like to launch pengines.swi-prolog.org to
	run a public demo.  The stuff you created is one.  This would
	make another nice demo.

On 02/09/2014 05:00 PM, Torbjörn Lager wrote:
> One thing I like about Prolog is that most things can be explored
> interactively, at the ?- prompt. It's a good way to explore a new
> library for example. Having the name(<name>) option in
> pengine_create/1 is one way of making this more convenient. Already at
> this point, we can do:
>
> ?- pengine_create([name(a)]).
> true.
>
> ?- pengine_create([name(b)]).
> true.
>
> ?- pengine_ask(a, member(A, [a,b,c])).
> true.
>
> ?- pengine_ask(b, append(Xs, Ys, [a,b,c]), [template(Xs-Ys)]).
> true.
>
> ?- pengine_next(b).
> true.
>
> ?- pengine_next(a).
> true.
>
> ?- pengine_event_loop(writeln).
> create(eddcb314-9192-11e3-a036-3c075453f481,true)
> create(f1d773aa-9192-11e3-b8e0-3c075453f481,true)
> success(eddcb314-9192-11e3-a036-3c075453f481,[member(a,[a,b,c])],true)
> success(f1d773aa-9192-11e3-b8e0-3c075453f481,[[]-[a,b,c]],true)
> success(f1d773aa-9192-11e3-b8e0-3c075453f481,[[a]-[b,c]],true)
> success(eddcb314-9192-11e3-a036-3c075453f481,[member(b,[a,b,c])],true)
>
>
> The problem is that you don't get any responses until you call
> pengine_event_loop/1, and then you'll get all of them at the same
> time. Also, once you have called pengine_event_loop/1, you won't be
> able to send more commands to your pengines. :-(
>
> Fortunately, I think this can be fixed by adding an option
> 'asynch(Boolean)' to pengine_event_loop/1. (Boolean should most likely
> be false by default, since using asynch(true) uses an extra thread.)
> Now, we would be able to START the interaction by starting the event
> loop:
>
> ?- pengine_event_loop(writeln, [asynch(true)]).
> true.
>
> ?- pengine_create([name(a)]).
> create(eddcb314-9192-11e3-a036-3c075453f481,true)
> true.
>
> ?- pengine_create([name(b)]).
> create(f1d773aa-9192-11e3-b8e0-3c075453f481,true)
> true.
>
> ?- pengine_ask(a, member(A, [a,b,c])).
> success(eddcb314-9192-11e3-a036-3c075453f481,[member(a,[a,b,c])],true)
> true.
>
> ?- pengine_ask(b, append(Xs, Ys, [a,b,c]), [template(Xs-Ys)]).
> success(f1d773aa-9192-11e3-b8e0-3c075453f481,[[]-[a,b,c]],true)
> true.
>
> ?- pengine_next(b).
> success(f1d773aa-9192-11e3-b8e0-3c075453f481,[[a]-[b,c]],true)
> true.
>
> ?- pengine_next(a).
> success(eddcb314-9192-11e3-a036-3c075453f481,[member(b,[a,b,c])],true)
> true.
>
> ?-
>
> Instead of using writeln/1 as the handler, we could probably use a
> predicate (maybe pengine_write_event/1) that replaced IDs with names,
> like so:
>
> ?- pengine_event_loop(pengine_write_event, [asynch(true)]).
> true.
>
> ?- pengine_create([name(a)]).
> create(a,true)
> true.
>
> ?- pengine_create([name(b)]).
> create(b,true)
> true.
>
> ?- pengine_ask(a, member(A, [a,b,c])).
> success(a,[member(a,[a,b,c])],true)
> true.
>
> ?- pengine_ask(b, append(Xs, Ys, [a,b,c]), [template(Xs-Ys)]).
> success(b,[[]-[a,b,c]],true)
> true.
>
> ?- pengine_next(b).
> success(b,[[a]-[b,c]],true)
> true.
>
> ?- pengine_next(a).
> success(a,[member(b,[a,b,c])],true)
> true.
>
> ?- pengine_create([name(c)]).
> create(c,true)
> true.
>
> ?- pengine_ask(c, (between(1, 3, X), pengine_output(X), fail).
> output(c,1)
> output(c,2)
> output(c,3)
> success(c,[(between(1, 3, X), pengine_output(X), fail)],true)
> true.
>
> Adding the asynch option to pengine_create/1 might be a good idea. Thoughts?
>
> - Torbjörn
>