CSCI 3137 - Logic Programming with Prolog

SWI-Prolog Overview

• SWI-Prolog is a free implementation of the Prolog programming language, developed at the University of Amsterdam.
• Available for download at http://swi-prolog.org, with a web-based version, SWISH, accessible at http://swish.swi-prolog.org.
• Prolog files use the .pl extension.

Prolog Program Structure

• Programs consist of facts, predicates, relations defined as true, and rules that establish relationships between predicates.
• Distinction exists between functional programming (using functions) and logical programming (using predicates).

Querying in Prolog

• Prolog uses a querying system instead of traditional execution.
• Queries determine if a statement can be proven from existing facts and rules.
• The predicate plus(Addend1, Addend2, Sum) checks if Addend1 + Addend2 = Sum.
• Examples of queries:
  • ?- plus(1, 2, 3). asks if 1 + 2 equals 3.
  • ?- plus(1, 2, Sum). seeks the value of Sum that satisfies the equation.

Atoms in Prolog

• Atoms serve as tokens with meaning defined by the programmer (e.g., socrates could represent a person or a pet).
• Example: GP is a grandparent of GC if there exists a parent-child relationship.

Query Resolution Mechanism

• Prolog resolves queries by unifying them with facts or rules.
• A successful unification with a fact indicates truth; with a rule, the rule's body becomes the subgoal.
• Multiple potential unifying facts/rules create choice points in Prolog.

Handling Query Failure

• A query failure signifies that a statement cannot be proven, not necessarily that it is false.

Conjunction in Prolog

• Expressions can be evaluated for equality or inequality using =:= and =\= respectively.
• Example rules show how comparisons between expressions are made.

Arithmetic Operations

• Term1 = Term2 denotes unification, while Expr1 =:= Expr2 represents mathematical equality.
• Example: 1 =:= 1.0 is true, but 1 = 1.0 is false due to type differences.

Lists in Prolog

• Lists are structured as a head element(s) followed by a tail list, similar to structures in Scheme.

Variable Unification

• Unifying two free variables creates a single variable with multiple designations.
• Example: A = B links both names to the same unidentified object.

Unification of Compound Terms

• Compound terms unify only if they share the same name and arity, with corresponding arguments also unifying.
• Examples:
  • f(a) = f(a) is valid.
  • f(a) = g(a) fails due to differing names.

Rules and Facts in Prolog

• Facts convey unconditional truths and are declared with syntax ending in a period, e.g., parent(marge, maggie).
• Rules derive new facts from known ones, formatted as head :- term_1, term_2,..., term_n.
• Example: grandparent(GP, GC) :- parent(GP, P), parent(P, GC). demonstrates how to establish grandparent relationships through parenthood.

This quiz covers the fundamental principles of logic programming using SWI-Prolog, including installation and usage details. Explore the features of this powerful programming language and understand its application in various programming contexts.