while_call.pl

/*
I thought something like this already existed somewhere?

But anyhow it doesn't right? 
Though how should this be written?  Byrd box? debugger model?

*/


call_while(Setup,Goal,Undo):-     
    once(Setup),
     (Goal
       *-> 
     (once(Undo);(once(Setup),fail))
       ;
      (Undo,!,fail)).


/ *Example usages: */

with_prolog_flag(Flag,Value,Goal):-
     current_prolog_flag(Flag,Was),
     call_while( set_prolog_flag(Flag,Value),
                 Goal,
                 set_prolog_flag(Flag,Was)).


% Trace that is not like once/1
no_trace(Goal):- 
   (   
   notrace((tracing,notrace))
    -> 
  ('$leash'(OldL, OldL),
   '$visible'(OldV, OldV), 
       call_while(
       notrace((visible(-all),leash(-all),leash(+exception),visible(+exception)))
       Goal,
       notrace(('$leash'(_, OldL),'$visible'(_, OldV),trace))))
  ; 
  Goal).
 	

% Trace non interactively
with_trace_non_interactive(Goal):- 
  (   tracing-> Undo=trace ; Undo = notrace ),
    
  '$leash'(OldL, OldL),
  '$visible'(OldV, OldV),
   call_while(
       notrace((visible(+all),leash(-all),leash(+exception),trace)),
       Goal,
       notrace(('$leash'(_, OldL),'$visible'(_, OldV),Undo)))