do_expander('=',_,X,X):-!.
do_expander(':',_,X,Y):- !, get_type(X,Y)*->X=Y.

get_type(Arg,Type):- eval_H(['get-type',Arg],Type).


%! eval_true(+X) is semidet.
% Evaluates the given term X and succeeds if X is not a constraint (i.e. \+ iz_conz(X)) and is callable, and calling X succeeds.
%
% If X is not callable, this predicate will attempt to evaluate the arguments of X (using eval_args/2) and succeed if the result is not False.
eval_true(X):- \+ iz_conz(X), callable(X), call(X).
eval_true(X):- eval_args(X,Y), once(var(Y) ; \+ is_False(Y)).

eval(Depth,Self,X,Y):- eval('=',_,Depth,Self,X,Y).
eval(Eq,RetType,Depth,Self,X,Y):-
  catch_metta_return(eval_args(Eq,RetType,Depth,Self,X,Y),Y).

%:- set_prolog_flag(gc,false).
/*
eval_args(Eq,RetTyp e,Depth,Self,X,Y):-
   locally(set_prolog_flag(gc,true),
      rtrace_on_existence_error(
     eval(Eq,RetType,Depth,Self,X,Y))).
*/


%! eval_args(+X,-Y) is semidet.
eval_args(X,Y):- current_self(Self), eval_args(500,Self,X,Y).
%eval_args(Eq,RetType,Depth,_Self,X,_Y):- forall(between(6,Depth,_),write(' ')),writeqln(eval_args(Eq,RetType,X)),fail.
eval_args(Depth,Self,X,Y):- eval_args('=',_RetType,Depth,Self,X,Y).

eval_args(_Eq,_RetType,_Dpth,_Slf,X,Y):- var(X),nonvar(Y),!,X=Y.
eval_args(_Eq,_RetType,_Dpth,_Slf,X,Y):- notrace(self_eval(X)),!,Y=X.
eval_args(Eq,RetType,Depth,Self,X,Y):-
    notrace(nonvar(Y)), var(RetType),
    get_type(Depth,Self,Y,WasType),
    can_assign(WasType,RetType),
    nonvar(RetType),!,
    eval_args(Eq,RetType,Depth,Self,X,Y).
eval_args(Eq,RetType,Depth,Self,X,Y):- notrace(nonvar(Y)),!,
   eval_args(Eq,RetType,Depth,Self,X,XX),evals_to(XX,Y).


eval_args(Eq,RetType,_Dpth,_Slf,[X|T],Y):- T==[], number(X),!, do_expander(Eq,RetType,X,YY),Y=[YY].

/*
eval_args(Eq,RetType,Depth,Self,[F|X],Y):-
  (F=='superpose' ; ( option_value(no_repeats,false))),
  notrace((D1 is Depth-1)),!,
  eval_args(Eq,RetType,D1,Self,[F|X],Y).
*/

eval_args(Eq,RetType,Depth,Self,X,Y):- atom(Eq),  ( Eq \== ('='),  Eq \== ('match')) ,!,
   call(call,Eq,'=',RetType,Depth,Self,X,Y).

eval_args(_Eq,_RetType,_Dpth,_Slf,X,Y):- self_eval(X),!,Y=X.
eval_args(Eq,RetType,Depth,Self,X,Y):-
  eval_00(Eq,RetType,Depth,Self,X,Y).
%eval_ret(Eq,RetType,1000,Self,X,Y):- !,
%  catch_metta_return(eval_ret(Eq,RetType,99,Self,X,Y),Y).

eval_ret(Eq,RetType,Depth,Self,X,Y):-
    eval_00(Eq,RetType,Depth,Self,X,Y), is_returned(Y).

catch_metta_return(G,Y):-
 catch(G,metta_return(Y),ignore(retract(thrown_metta_return(Y)))).

allow_repeats_eval_(_):- !.
allow_repeats_eval_(_):- option_value(no_repeats,false),!.
allow_repeats_eval_(X):- \+ is_list(X),!,fail.
allow_repeats_eval_([F|_]):- atom(F),allow_repeats_eval_f(F).
allow_repeats_eval_f('superpose').
allow_repeats_eval_f('collapse').


:- nodebug(metta(overflow)).
eval_00(_Eq,_RetType,_Depth,_Slf,X,Y):- self_eval(X),!,X=Y.
eval_00(Eq,RetType,Depth,Self,X,YO):-
   eval_01(Eq,RetType,Depth,Self,X,YO).