(is_True(TF) -> eval_args(Eq,RetType,Depth,Self,Then,Res) ;
      (!, fail,Res = [],!)).

eval_20(Eq,RetType,Depth,Self,['if',Cond,Then],Res):- !,
   eval_args(Eq,'Bool',Depth,Self,Cond,TF),
   (is_True(TF) -> eval_args(Eq,RetType,Depth,Self,Then,Res) ;
      (!, fail,Res = [],!)).


eval_20(Eq,RetType,_Dpth,_Slf,[_,Nothing],NothingO):-
   'Nothing'==Nothing,!,do_expander(Eq,RetType,Nothing,NothingO).


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% =================================================================
%  CONS/CAR/CDR
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% =================================================================



into_pl_list(Var,Var):- var(Var),!.
into_pl_list(Nil,[]):- Nil == 'Nil',!.
into_pl_list([Cons,H,T],[HH|TT]):- Cons == 'Cons', !, into_pl_list(H,HH),into_pl_list(T,TT),!.
into_pl_list(X,X).

into_metta_cons(Var,Var):- var(Var),!.
into_metta_cons([],'Nil'):-!.
into_metta_cons([Cons, A, B ],['Cons', AA, BB]):- 'Cons'==Cons, no_cons_reduce, !,
  into_metta_cons(A,AA), into_metta_cons(B,BB).
into_metta_cons([H|T],['Cons',HH,TT]):- into_metta_cons(H,HH),into_metta_cons(T,TT),!.
into_metta_cons(X,X).

into_listoid(AtomC,Atom):- AtomC = [Cons,H,T],Cons=='Cons',!, Atom=[H,[T]].
into_listoid(AtomC,Atom):- is_list(AtomC),!,Atom=AtomC.
into_listoid(AtomC,Atom):- typed_list(AtomC,_,Atom),!.

:- if( \+  current_predicate( typed_list / 3 )).
typed_list(Cmpd,Type,List):-  compound(Cmpd), Cmpd\=[_|_], compound_name_arguments(Cmpd,Type,[List|_]),is_list(List).
:- endif.

%eval_20(Eq,RetType,Depth,Self,['colapse'|List], Flat):- !, maplist(eval_args(Eq,RetType,Depth,Self),List,Res),flatten(Res,Flat).

%eval_20(Eq,RetType,Depth,Self,['flatten'|List], Flat):- !, maplist(eval_args(Eq,RetType,Depth,Self),List,Res),flatten(Res,Flat).


eval_20(Eq,RetType,_Dpth,_Slf,['car-atom',Atom],CAR_Y):- !, Atom=[CAR|_],!,do_expander(Eq,RetType,CAR,CAR_Y).
eval_20(Eq,RetType,_Dpth,_Slf,['cdr-atom',Atom],CDR_Y):- !, Atom=[_|CDR],!,do_expander(Eq,RetType,CDR,CDR_Y).

eval_20(Eq,RetType,Depth,Self,['Cons', A, B ],['Cons', AA, BB]):- no_cons_reduce, !,
  eval_args(Eq,RetType,Depth,Self,A,AA), eval_args(Eq,RetType,Depth,Self,B,BB).

%eval_20(_Eq,_RetType,Depth,Self,['::'|PL],Prolog):-  maplist(as_prolog(Depth,Self),PL,Prolog),!.
%eval_20(_Eq,_RetType,Depth,Self,['@'|PL],Prolog):- as_prolog(Depth,Self,['@'|PL],Prolog),!.

eval_20(Eq,RetType,Depth,Self,['Cons', A, B ],[AA|BB]):- \+ no_cons_reduce, !,
   eval_args(Eq,RetType,Depth,Self,A,AA), eval_args(Eq,RetType,Depth,Self,B,BB).



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