Recursion in Squirrel

Our example demonstrates recursion, a fundamental concept in programming. Here’s how it’s implemented in Java:

public class Recursion {
    // This fact method calls itself until it reaches the base case of fact(0).
    public static int fact(int n) {
        if (n == 0) {
            return 1;
        }
        return n * fact(n - 1);
    }

    public static void main(String[] args) {
        System.out.println(fact(7));

        // In Java, we can use anonymous inner classes to create recursive lambdas
        RecursiveFunction<Integer, Integer> fib = new RecursiveFunction<Integer, Integer>() {
            @Override
            public Integer apply(Integer n) {
                if (n < 2) {
                    return n;
                }
                return apply(n - 1) + apply(n - 2);
            }
        };

        System.out.println(fib.apply(7));
    }
}

// This interface allows us to create recursive lambda functions
interface RecursiveFunction<T, R> {
    R apply(T t);
}

In this Java example, we’ve implemented the factorial function recursively, similar to the original. The fact method calls itself with n-1 until it reaches the base case of n == 0.

For the Fibonacci sequence, Java doesn’t have direct support for recursive closures like some functional programming languages. However, we can achieve similar functionality using an anonymous inner class that implements a custom RecursiveFunction interface. This allows us to create a recursive lambda-like function.

To run this program:

$ javac Recursion.java
$ java Recursion
5040
13

The output shows the factorial of 7 (5040) and the 7th Fibonacci number (13).

While Java doesn’t have the exact same syntax for closures as some other languages, this approach with anonymous inner classes provides similar functionality for creating recursive functions on the fly.