Interactive programming with pengines

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

-- 
Torbjörn Lager
Professor of General and Computational Linguistics
Department of Philosophy, Linguistics and Theory of Science
University of Gothenburg
Box 200, SE-405 30 Gothenburg, Sweden
Phone: +46317864962