Question

i am doing a Prolog project and below is my code.

:- dynamic yes/1,no/1.
:- dynamic n_angle/1.

go :- hypothesize(Shape),
  write('Yes I know the shape you talking about is a '),
  write(Shape),
  write('!!!!'),
  undo.

hypothesize(circle)          :- circle,!.

circle :- not(verify(width)),
      verify(radius),
      not(verify(height)),
      verify(diameter_equal_2_radius).

ask(Question):-

write('Has the shape '),
write(Question),
write('?'),
read(Response),
nl,
((Response == yes ; Response == y)
  -> assert(yes(Question));
     assert(no(Question)), fail).

verify(S) :-
   (yes(S) ->  true ;
   (no(S)  ->  fail ;
   ask(S))).

save_file:- tell('D:ansSave.txt').

/* undo all yes/no assertions */
undo :- retract(yes(_)),fail.
undo :- retract(no(_)),fail.
undo :- retract(n_angle(_)),fail.
undo.

and the result will be like this.

?- go.
Has the shape width?n.

Has the shape radius?y.

Has the shape height?n.

Has the shape diameter_equal_2_radius?y.

Yes I know the shape you talking about is a circle!!!!

true.

i want to save the result as shown above to a txt file.

but when i try to put the save_file to the ask function

ask(Question):-
 save_file,
write('Has the shape '),
write(Question),
write('?'),
read(Response),
nl,
told,
((Response == yes ; Response == y)
  -> assert(yes(Question));
     assert(no(Question)), fail).

it will overwrite the result every time. can anyone tell me how to solve this ? thanks in advance.

Answer 1

If you don’t want to overwrite previous file content, consider using append/1.

So your rule must be:

save_file:- append('D:ansSave.txt').