check_returnval(Eq,RetType,RetVal).


nd_ignore(Goal):- call(Goal)*->true;true.


% =================================================================
% =================================================================
% =================================================================
%  AND/OR
% =================================================================
% =================================================================
% =================================================================

is_True(T):- atomic(T), T\=='False', T\==0.

is_and(S):- \+ atom(S),!,fail.
%is_and(',').
is_and(S):- is_and(S,_).

is_and(S,_):- \+ atom(S),!,fail.
%is_and('and','True').
is_and('and2','True').
%is_and('#COMMA','True'). %is_and(',','True').  % is_and('And').

is_comma(C):- var(C),!,fail.
is_comma(',').
is_comma('{}').

bool_xor(A,B) :- (A == 'True'; B == 'True'), \+ (A == B).

eval_20(Eq,RetType,Depth,Self,['and',X,Y],TF):- !,
    as_tf(( (eval_args_true(Eq,RetType,Depth,Self,X),
             eval_args_true(Eq,RetType,Depth,Self,Y))), TF).


eval_20(Eq,RetType,Depth,Self,['or',X,Y],TF):- !,
  as_tf(( (eval_args_true(Eq,RetType,Depth,Self,X);
           eval_args_true(Eq,RetType,Depth,Self,Y))), TF).

eval_20(Eq,RetType,Depth,Self,['xor',X,Y],TF):- !,
  as_tf(  (eval_args_true(Eq,RetType,Depth,Self,X)),  XTF),  % evaluate X
  as_tf(  (eval_args_true(Eq,RetType,Depth,Self,Y)),  YTF),  % evaluate Y
  as_tf(  (bool_xor(XTF,YTF))              ,   TF).


eval_20(Eq,RetType,Depth,Self,['not',X],TF):- !,
   as_tf(( \+ eval_args_true(Eq,RetType,Depth,Self,X)), TF).


% ================================================
% === function / return of minimal metta
eval_20(Eq,RetType,Depth,Self,['function',X],Res):- !, gensym(return_,RetF),
  RetUnit=..[RetF,Res],
  catch(locally(nb_setval('$rettag',RetF),
           eval_args(Eq,RetType,Depth,Self,X, Res)),
        return(RetUnitR),RetUnitR=RetUnit).
eval_20(Eq,RetType,Depth,Self,['return',X],_):- !,
  nb_current('$rettag',RetF),RetUnit=..[RetF,Val],
  eval_args(Eq,RetType,Depth,Self,X, Val), throw(return(RetUnit)).
% ================================================

% ================================================
% === catch / throw of mettalog
eval_20(Eq,RetType,Depth,Self,['catch',X,EX,Handler],Res):- !,
  catch(eval_args(Eq,RetType,Depth,Self,X, Res),
         EX,eval_args(Eq,RetType,Depth,Self,Handler, Res)).
eval_20(Eq,_TRetType,Depth,Self,['throw',X],_):- !,
  eval_args(Eq,_RetType,Depth,Self,X, Val), throw(Val).
% ================================================

eval_20(Eq,RetType,Depth,Self,['number-of',X],N):- !,
   findall_eval(Eq,RetType,Depth,Self,X,ResL),
   length(ResL,N), ignore(RetType='Number').

eval_20(Eq,RetType,Depth,Self,['number-of',X,N],TF):- !,
   findall_eval(Eq,RetType,Depth,Self,X,ResL),
   length(ResL,N), true_type(Eq,RetType,TF).

eval_20(Eq,RetType,Depth,Self,['findall!',Template,X],ResL):- !,