Computer Science 3675
Summer 2002
Practice questions for quiz 5

1. True or false.

   1. When a variable occurs in a logic programming goal, the interpreter is being asked whether that goal holds for all values of the variable.

   2. In logic programming, a variable in an axiom might be used as an input variable sometimes, and as an output variable at other times, when computation uses that axiom.

   3. Cuts are used to reduce memory requirements and to speed up computation.

   4. Negation (the not predicate) in Prolog is mathematically correct negation, and goal not(X = 5) binds variable X to some value that is not equal to 5.

2. Unification is a form of pattern matching. Which of the following is not a characteristic of unification?

   1. Unification never changes the binding of a bound variable.
   2. Unification is symmetric; unifying A with B has exactly the same effect as unifying B with A.
   3. Unification is very slow, and is only used rarely during computations of logic programs.
   4. Unification can bind unbound variables.

3. Are backtracking and exception handling the same thing? For example, can you use the exception handling mechanism of Java to do backtracking?

4. What is one important motivation for including exception handling in a programming language?

5. In a logic programming style, write axioms for computing predicate samelength(X,Y), which is true just when X and Y are lists that have the same length.

6. In a logic programming style, write axioms for computing predicate allsame(X), which is true just when all members of list X are the same. For example, allsame([5,5,5]) is true, as is allsame([a,a]), but allsame([2,4,4]) is false. Note that allsame([]) is true, and allsame([b]) is true.

7. Show the logic programming search tree for goal (member(X,[3,4,5]), member(X,[4])), up to the point where a success is found. The definition of the member predicate is as follows, written in Prolog syntax.

         member(M, [M|X]).
         member(M, [X|T]) :- member(M, T).