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%  Copyright 2016 Metagol authors
%  Copyright 2018-2019 Paulo Moura
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:- set_logtalk_flag(hook, metagol).


:- object(higher_order2,
	implements(metagol_example_protocol),
	extends(metagol)).

	:- uses(integer, [succ/2]).
	:- uses(list, [length/2, valid/1 as is_list/1]).

	%% background knowledge
	my_double(A,B) :-
	    integer(A),
	    (ground(B) -> integer(B); true),
	    B is A*2.
	my_succ(A,B) :-
	    integer(A),
	    (ground(B) -> integer(B); true),
	    succ(A,B).
	my_length(A,B) :-
	    is_list(A),
	    (ground(B) -> integer(B); true),
	    length(A,B).

	:- meta_predicate(map(*, *, 2)).
	map([],[],_F).
	map([A|As],[B|Bs],F):-
		call(F,A,B),
		map(As,Bs,F).

	%% allow metagol to use my_succ in the body of a clause
	body_pred(my_succ/2).
	body_pred(my_double/2).
	body_pred(my_length/2).

	%% metarules
	metarule([P,Q,F], [P,A,B], [[Q,A,B,F]]).
	metarule([P,Q,R], [P,A,B], [[Q,A,C],[R,C,B]]).

	%% interpreted BK
	ibk([map,[],[],_],[]).
	ibk([map,[A|As],[B|Bs],F],[[F,A,B],[map,As,Bs,F]]).

	learn(Clauses) :-
		A = [[a],[a,a],[a,a,a],[a,a,a,a]],
		B = [3,5,7,9],
		^^learn([f(A,B)], [], Prog),
		^^program_to_clauses(Prog, Clauses).

	learn :-
		learn(Clauses),
		^^pprint_clauses(Clauses).

:- end_object.
