/* 

  Meta interpreter in Picat v3.

  Run as 
   $ picat -g bp.go meta_interpreter_bp_v3.pi

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

*/

% This loads Prolog so we don't have to use bp.<...>
import bp.

main :- go.

% Picat/B-Prolog requires that the clauses are asserted
% for use with clause/2-3
go :-
  assert(memberx(X,[X|_])),
  assert((memberx(X,[_|R]) :- memberx(X,R))),
  clause_tree(memberx(X,[a,b,c])),
  writeln(X),
  fail,
    
  nl.

go :- true.


go2 :-
  clause_tree((Y is 3, Y <  5)),
  writeln(Y),
  nl.

go2. 

% memberx(X,[X|_]). 
% memberx(X,[_|R]) :- memberx(X,R). 


% From
% https://www.cpp.edu/~jrfisher/www/prolog_tutorial/pt_framer.html
% https://www.cpp.edu/~jrfisher/www/prolog_tutorial/3_3.html
% clause_tree(true) :- !.      /* true leaf */ 
% clause_tree((G,R)) :-
%    !, 
%    clause_tree(G),
%    clause_tree(R).           /* search each branch */ 
% clause_tree(G) :-
%    clause(G,Body), 
%    clause_tree(Body).        /* grow branches */ 

clause_tree(true) :- !.
clause_tree((G,R)) :-
   !,
   clause_tree(G), 
   clause_tree(R).
clause_tree(G) :-
   predicate_property(G,built_in),
   call(G).              %% let Prolog do it
clause_tree(G) :-
   clause(G,Body),
   clause_tree(Body).