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bricks

This folder contains an example of representation and handling of relations using events. We have instances of class brick and a binary brick_stack relation between the bricks. Every time we move a brick, we want the bricks on top of it to move along. If we break the stack by moving a middle brick, we want to automatically destroy the corresponding relation tuple.

It's instructive to use the debugger to better understand this example. Set spy points in all block instances and then activate the debugger.

Print Logtalk, Prolog backend, and kernel versions (if running as a notebook):

%versions

Start by loading the example and the required library files:

logtalk_load(bricks(loader)).

Create four bricks, all standing on the "ground" (use your imagination... ;-) (don't use message broadcasting syntax in order to workaround a XSB parser bug):

brick::new(a, [position-(8, 1)]), brick::new(b, [position-(6, 1)]), brick::new(c, [position-(4, 1)]), brick::new(d, [position-(2, 1)]).

<!-- true. -->

Set up an ASCII stack monitor so we can watch the bricks moving:

after_event_registry::set_monitor(_, move(_,_), _, stack_monitor).

<!-- true. -->

Ensure that top-level message goals generate events:

set_logtalk_flag(events, allow).

<!-- true. -->

Make the stack (don't use message broadcasting syntax in order to workaround a XSB parser bug):

brick_stack::add_tuple([c,d]), brick_stack::add_tuple([b,c]), brick_stack::add_tuple([a,b]).

<!-- |.c...... |.d...b.a --------- |.b...... |.c...... |.d.....a --------- |.a |.b |.c |.d --- true. -->

List all tuples:

forall(brick_stack::tuple(Tuple), (write(Tuple), nl)).

<!-- [c,d] [b,c] [a,b]

true. -->

List all before and after monitors:

before_event_registry::monitors(BeforeMonitors), after_event_registry::monitors(AfterMonitors).

<!-- AfterMonitors = [brick_stack, stack_monitor], BeforeMonitors = [brick_stack]. -->

Move all stack to new position by moving bottom brick; check results:

d::move(9, 1).

<!-- |.a....... |.b....... |.c....... |........d ---------- |.a....... |.b....... |........c |........d ---------- |.a....... |........b |........c |........d ---------- |........a |........b |........c |........d ---------- true. -->

Check results:

a::position(Xa, Ya), b::position(Xb, Yb), c::position(Xc, Yc), d::position(Xd, Yd).

<!-- Xa = 9, Xb = 9, Xc = 9, Xd = 9, Ya = 4, Yb = 3, Yc = 2, Yd = 1. -->

List all tuples:

forall(brick_stack::tuple(Tuple), (write(Tuple), nl)).

<!-- [c,d] [b,c] [a,b]

true. -->

Break the stack in half by moving b to the "ground":

b::move(3, 1).

<!-- |........a |......... |........c |..b.....d ---------- |..a.....c |..b.....d ---------- true. -->

Check results:

a::position(Xa, Ya), b::position(Xb, Yb), c::position(Xc, Yc), d::position(Xd, Yd).

<!-- Xa = 3, Xb = 3, Xc = 9, Xd = 9, Ya = 2, Yb = 1, Yc = 2, Yd = 1. -->

List all tuples:

forall(brick_stack::tuple(Tuple), (write(Tuple), nl)).

<!-- [c,d] [a,b]

true. -->

Create a new brick_stack tuple and check results:

brick_stack::add_tuple([d, a]).

<!-- |..d...... |..a.....c |..b...... ---------- |..c |..d |..a |..b ---- true. -->

Check results:

a::position(Xa, Ya), b::position(Xb, Yb), c::position(Xc, Yc), d::position(Xd, Yd).

<!-- Xa = 3, Xb = 3, Xc = 3, Xd = 3, Ya = 2, Yb = 1, Yc = 4, Yd = 3. -->

List all tuples:

forall(brick_stack::tuple(Tuple), (write(Tuple), nl)).

<!-- [c,d] [a,b] [d,a]

true. -->

Move the stack to new position by moving bottom brick:

b::move(5, 1).

<!-- |..c.. |..d.. |..a.. |....b ------ |..c.. |..d.. |....a |....b ------ |..c.. |....d |....a |....b ------ |....c |....d |....a |....b ------ true. -->

Check results:

a::position(Xa, Ya), b::position(Xb, Yb), c::position(Xc, Yc), d::position(Xd, Yd).

<!-- Xa = 5, Xb = 5, Xc = 5, Xd = 5, Ya = 2, Yb = 1, Yc = 4, Yd = 3. -->

List all tuples:

forall(brick_stack::tuple(Tuple), (write(Tuple), nl)).

<!-- [c,d] [a,b] [d,a]

true. -->

Clean up instances, tuples and monitors:

brick_stack::remove_all_tuples.

<!-- true. -->

Unset stack_monitor as an event monitor:

after_event_registry::del_monitors(_, _, _, stack_monitor).

<!-- true. -->

Delete all bricks:

brick::delete_all.

<!-- true. -->