11 Rules

Introduction

Prolog has two kinds of programming statements: Facts and rules. So far, we have looked at facts. But Prolog with only facts is only half a Prolog. In order to utilize the power of Prolog, rules are needed. This chapter is on Prolog rules.

Overview of this chapter

We will first give an example of a Prolog rule. Then we will introduce some terminology necessary for talking aboout rules and what is called Prolog clauses (facts is one kind of clause; rules are the other kind of clause). After that, we will say a little about when two occurrences of a variable name refers to the same variable (variable scoping rule). After that, we will present a technique for solving a common programming problem in Prolog: How do we return a value from a rule. Finally, there is a quiz.


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