Prolog Programming Language Cheatsheet

Prolog, short for “Programming in Logic,” is a declarative programming language designed for symbolic reasoning and manipulation. It is particularly well-suited for tasks involving rule-based systems, artificial intelligence, and knowledge representation. If you’re diving into Prolog or need a quick reference guide, this cheatsheet will help you get started and navigate the essentials of the language.

1. Basic Syntax:

• Facts: likes(john, pizza). friend(jane, alice).
• Rules: mortal(X) :- human(X). human(socrates).
• Queries:
  prolog ?- likes(john, pizza). ?- mortal(socrates).

2. Variables:

• Variables in Prolog begin with an uppercase letter or an underscore.

   ?- likes(john, X).

3. Lists:

• Lists are a fundamental data structure in Prolog.

   colors([red, green, blue]).

• Accessing elements in a list:

   ?- colors(Colors), nth0(1, Colors, SecondColor).

4. Predicates:

• Built-in predicates are essential for manipulating data and performing operations.

   ?- length([1, 2, 3], Len).
   ?- append([1, 2], [3, 4], Result).

5. Arithmetic Operations:

   ?- X is 3 + 4.

6. Cut Operator (!):

• Cuts off backtracking, committing to the current choice point.

   likes(john, pizza) :- !.
   likes(john, sushi).

7. Recursion:

• Prolog excels in recursive definitions.

   factorial(0, 1).
   factorial(N, Result) :-
       N > 0,
       Prev is N - 1,
       factorial(Prev, PrevResult),
       Result is N * PrevResult.

8. Conjunction and Disjunction:

• Conjunction (,): ancestor(X, Y) :- parent(X, Z), ancestor(Z, Y).
• Disjunction (;):
  prolog color(X, green) :- leaf(X). color(X, brown) :- trunk(X).

9. Dynamic Predicates:

• Modify facts or rules at runtime.

   asserta(fact(X)) :- !, asserta(X).

10. Debugging:

• Use trace. to enable tracing for better debugging.

   ?- trace.

Conclusion:

Prolog’s unique paradigm and elegant syntax make it a powerful tool for tasks involving logical reasoning and knowledge representation. This cheatsheet covers the basics, providing a foundation for exploring more advanced features and applications in Prolog programming. As you delve deeper into the language, experimenting with different predicates, rules, and constructs will enhance your understanding and proficiency.

You can refer to the official prolog documentation for more in-depth information on each topic.