/* 

  Explanation-Based Generalization (EBG) in Picat v3.

  This is a port of the program minihyper.pl in
  I. Bratko, "Prolog Programming for Artificial Intelligence", 4th edn.,
  Pearson Education / Addison-Wesley 2012
  Page 621ff (Figures 25.6, 25.7)

  This is the gift example from figure 25.6.

  This Picat model was created by Hakan Kjellerstrand, hakank@gmail.com
  See also my Picat page: http://www.hakank.org/picat/

*/

import ebg_v3.

main => go.

% example from page 624 and 625
go ?=>
  load_gifts,
  ebg($gives(john,john,chocolate),$gives(X,Y,Z),Condition),
  number_vars([X,Y,Z]),
  println(condition=Condition),
  
  nl.

go => true.

% another example from page 624
go2 ?=>
  load_gifts,
  ebg($gives(john,annie,tennis_racket),$gives(X,Y,Z),Condition),
  number_vars([X,Y,Z]),
  println(condition=Condition),
  
  nl.

go2 => true.




%  Figure 25.6  Two problem definitions for explanation-based generalization.

% For compatibility with some Prologs the following predicates
% are defined as dynamic:

% :- dynamic gives/3, would_please/2, would_comfort/2, feels_sorry_for/2, 
%    go/3, move/2, move_list/2.

% A domain theory: about gifts

% hakank: Load predicates to bp context
load_gifts :- 
  bp.assertz($(gives( Person1, Person2, Gift)  :- likes( Person1, Person2), would_please( Gift, Person2))),
  bp.assertz($(gives( Person1, Person2, Gift)  :- feels_sorry_for( Person1, Person2), would_comfort( Gift, Person2))),
  bp.assertz($(would_please( Gift, Person) :- needs( Person, Gift))),
  bp.assertz($(would_comfort( Gift, Person)  :- likes( Person, Gift))),
  bp.assertz($(feels_sorry_for( Person1, Person2)  :- likes( Person1, Person2), sad( Person2))),
  bp.assertz($(feels_sorry_for( Person, Person)  :- sad( Person))).

% Operational predicates

operational( likes( _, _)).
operational( needs( _, _)).
operational( sad( _)).

% An example situation

likes( john, annie).
likes( annie, john).
likes( john, chocolate).
needs( annie, tennis_racket).
sad( john).

% % Another domain theory: about lift movement

% %  go( Level, GoalLevel, Moves)  if
% %    list of moves Moves brings lift from Level to GoalLevel

% go( Level, GoalLevel, Moves)  :-
%   move_list( Moves, Distance),         % A move list and distance travelled
%   Distance =:= GoalLevel - Level.

% move_list( [], 0).

% move_list( [Move1 | Moves], Distance + Distance1)  :-
%   move_list( Moves, Distance),
%   move( Move1, Distance1).

% move( up, 1).
% move( down, -1).

% operational( A =:= B).