Computer Science 3675
Fall 2001
Practice questions for quiz 4

1. Write a clearly legible T to the left of each of the following that is true, and a clearly legible F to the left of each that is 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.

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

4. Using backtracking, write an Astarte program fragment that will print all solutions (x,y) to equation xy - 2x² + y = 10, where x and y are both integers in the range 0,...,100. Do not use a loop or recursion. Your program fragment can fail when it is done.

5. 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.

6. 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).