Some Exercises

To check you understand terms, unification and backtracking try the following. I may ask questions like these in the exam! (though they wouldn't be worth many marks).

1. Which of the following are valid Prolog terms:

• 23
• foo(X, bar(+(3,4)))
• Foo(x)
• +(fred, jim)
• 1+2.
• Alison Cawsey

2. Which of the following match, and for the ones that match, what are the resultant bindings.

• a(1, 2) = a(X, X).
• a(X, 3) = a(4, Y).
• a(a(3, X)) = a(Y).
• 1+2 = 3.
• X = 1+2.
• a(X, Y) = a(1, X).
• a(X, 2) = a(1, X).

3. For the following (silly) program, state what order the solutions will be returned given the query flies(X). (Your answer should be of the form X=soln1; X=soln2; etc).

  aeroplane(concorde).
  aeroplane(jumbo).
  on(fred, concorde).
  on(jim, no_18_bus).
  bird(percy).
  animal(leo).
  animal(tweety).
  animal(peter).
  has_feathers(tweety).
  has_feathers(peter).

  flies(X) :- bird(X).
  flies(X) :- aeroplane(X).
  flies(X) :- on(X, Y), aeroplane(Y).
  
  bird(X) :- animal(X), has_feathers(X).

Once you have worked out the answers by hand, check them using Prolog.