/* FLAGRO : Flag handling

                                                UTILITY
                                                Lawrence
                                                Updated: 11 September 81
*/

        %%%  FLAGRO requires no other modules



% Flags are stored in the database keyed under the Flag itself with
% the information packaged into a functor as follows:
%
%               Flag --> '$flag'(Flag,Value)
%
% This routine maintains these flags returning previous values as Old and
% updating the flag to New each time. The code actually checks to see if
% this updating really requires changing the database.
%


  flag(X,Old,New)
        :- nonvar(X),
           ( recorded(X,'$flag'(X,O),ID)  ;  O = 0 ),
           ( Old == New,
             !,
             Old = O        ;   !,
                                Old = O,
                                ( nonvar(ID), erase(ID)  ;  true ),
                                recorda(X,'$flag'(X,New),_)
           ),
           !.