% Define the parent relationship
parent(alice, bob).
parent(alice, charlie).
parent(bob, david).
parent(bob, emily).
parent(charlie, frank).
parent(charlie, grace).

% Define the male and female relationships
male(bob).
male(charlie).
male(david).
male(frank).

female(alice).
female(emily).
female(grace).

% Define the sister relationship
sister(X, Y) :-
    female(X),
    parent(Z, X), % X and Y have the same parent
    parent(Z, Y), % Y and X have the same parent
    X \= Y.      % X and Y are different individuals

% Query to find sisters
?- sister(X, Y). 

Prolog online compiler

Write, Run & Share Prolog code online using OneCompiler’s Prolog online compiler for free. It’s a simple and intuitive platform to experiment with logic programming in Prolog. OneCompiler supports standard Prolog syntax, great for learning, prototyping, and practicing logic-based problems.

About Prolog

Prolog (Programming in Logic) is a logic programming language associated with artificial intelligence and computational linguistics. It works through facts, rules, and queries, using a form of symbolic reasoning known as backward chaining. Prolog is declarative, meaning you describe what you want instead of how to compute it.

Sample Code

The following is a simple Prolog program that prints a greeting:

:- initialization(main).

main :-
    write('Hello, World!').

Syntax Basics

Facts

Facts represent basic assertions about the world.

likes(alice, pizza).
likes(bob, pasta).

Rules

Rules define logical relationships using facts.

friends(X, Y) :- likes(X, Z), likes(Y, Z).

Queries

Queries are used to find information based on facts and rules.

?- likes(alice, What).

Operators

OperatorDescription
:-Rule definition
,Logical AND
;Logical OR
=Unification

Lists

member(X, [X|_]).
member(X, [_|T]) :- member(X, T).

Recursion

Prolog heavily relies on recursion.

factorial(0, 1).
factorial(N, F) :-
  N > 0,
  N1 is N - 1,
  factorial(N1, F1),
  F is N * F1.

This guide provides a quick reference to Prolog programming syntax and features. Start writing Prolog code using OneCompiler’s Prolog online compiler today!