Operators and Arithmetic

Abstract

This chapter introduces operator notation for predicates and describes the operators provided for evaluating and comparing the values of arithmetic expressions, for testing for equality of either arithmetic expressions or terms and for testing for the negation of a goal or the disjunction of two goals.

After reading this chapter you should be able to:

• Convert unary and binary predicates to operators

• Evaluate arithmetic expressions and compare their values

• Test for equality of arithmetic expressions and terms

• Use the ’not’ and disjunction operators

Practical Exercise 4

• (1) This program is based on Animals Program 3, given in Chapter 2.

dog(fido). large(fido).

cat(mary). large(mary).

dog(rover). small(rover).

cat(jane). small(jane).

dog(tom). small(tom).

cat(harry).

dog(fred). large(fred).

cat(henry). large(henry).

cat(bill).

cat(steve). large(steve).

large(jim).

large(mike).

large_dog(X):- dog(X),large(X).

small_animal(A):- dog(A),small(A).

small_animal(B):- cat(B),small(B).

chases(X,Y):-

    large_dog(X),small_animal(Y),

    write(X),write(’ chases ’),write(Y),nl.

Convert the seven predicates used to operator form and test your revised program. The output should be the same as the output from the program above. Include directives to define the operators in your program.

• (2) Define and test a predicate which takes two arguments, both numbers, and calculates and outputs the following values: (a) their average, (b) the square root of their product and (c) the larger of (a) and (b).