After asking a question here about when exactly a Redo is called in Prolog with new variables, or when it is attempted with the same, I thought I figured it out. In the following piece of code, however, I thought that an additional Redo were to be called, but that does not seem to be the case.
My knowledge base is the following:
location(desk,office).
location(apple,kitchen).
location(flashlight,desk).
location('washing machine',cellar).
location(nani,'washing machine').
location(broccoli,kitchen).
location(crackers,kitchen).
location(computer,office).
edible(apple).
edible(crackers).
My query was
?-location(X,kitchen),edible(X).
with the following trace:
Call: (9) location(_5612, kitchen) ? creep
Exit: (9) location(apple, kitchen) ? creep
Call: (9) edible(apple) ? creep
Exit: (9) edible(apple) ? creep
X = apple ;
Redo: (9) location(_5612, kitchen) ? creep <====
Exit: (9) location(broccoli, kitchen) ? creep
Call: (9) edible(broccoli) ? creep
Fail: (9) edible(broccoli) ? creep
Redo: (9) location(_5612, kitchen) ? creep
Exit: (9) location(crackers, kitchen) ? creep
Call: (9) edible(crackers) ? creep
Exit: (9) edible(crackers) ? creep
X = crackers.
Why is there not an additional Redo after the first solution along the lines of Redo: (9) edible(apple) (which would then fail, before going on to the next Redo) since there is still another fact in the code with the functor edible, which would mean that there was a choice point that created? I found an annotated trace of the same query here. I will post a short snippet from it, because it has the additional Redo that I feel is missing here:
Can someone point me in the right direction as to what is to be expected in this case?
Thanks.