CSCI 3137 - Logic Programming with Prolog
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Questions and Answers

What happens when two free variables A and B are unified?

  • They refer to the same object. (correct)
  • They become bound to specific objects.
  • They no longer exist.
  • They can reference different objects.

    • Which of the following pairings is not valid for unification in compound terms?

  • f(a) = f(a)
  • f(A) = f(a)
  • f(a) = f(a, b) (correct)
  • f(a) = g(a) (correct)

    • Why can't the variable A in f(A, b) = f(a, A) be unified with both a and b?

  • Variables cannot be unified at all.
  • It can only be bound to one term at a time. (correct)
  • A is a compound term.
  • Both a and b are atoms.

    • What is the correct structure of a rule in Prolog?

    <p>head :- term_1, term_2,..., term_n. (C)</p> Signup and view all the answers

    Which of the following statements best describes facts in Prolog?

    <p>They express non-conditional statements that are true. (B)</p> Signup and view all the answers

    In the expression parent(GP, GC) :- parent(GP, P), parent(P, GC), what does GP represent?

    <p>A free variable. (D)</p> Signup and view all the answers

    What will the unification f(a) = f(b) return?

    <p>It will indicate a failure of unification. (C)</p> Signup and view all the answers

    If two compound terms have different names, what is the result of attempting to unify them?

    <p>The unification will fail. (D)</p> Signup and view all the answers

    Which statement about compound term unification is false?

    <p>Names of the terms can be different. (A)</p> Signup and view all the answers

    In the context of Prolog, what is the main purpose of rules?

    <p>To derive new facts from existing ones. (B)</p> Signup and view all the answers

    Study Notes

    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.

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    Related Documents

    09 - Prolog.pdf

    Description

    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.

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