PROLOG program to calculate factorial

Certainly! Here’s a Prolog program to calculate the factorial of a given number:

factorial(0, 1).
factorial(N, Result) :-
    N > 0,
    N1 is N - 1,
    factorial(N1, SubResult),
    Result is N * SubResult.

Explanation:

• The first clause of the factorial predicate states that the factorial of 0 is 1.
• The second clause of the factorial predicate recursively calculates the factorial of a number N. It checks if N is greater than 0, subtracts 1 from N to get N1, recursively calculates the factorial of N1, and multiplies it with N to get the final result.

You can use the program by querying the factorial predicate with a number. For example, to calculate the factorial of 5, you can execute the query:

factorial(5, Result).

The program will unify Result with the factorial value, which in this case will be 120.