// ============================================================================
// 014 — Recursion
// ============================================================================
// Handlers can call themselves recursively.
//
// Run:   soma run 014_recursion.cell factorial 6
// Expect: 720
//
// Run:   soma run 014_recursion.cell fibonacci 10
// Expect: 55

cell Recursive {

    // Classic factorial: n! = n * (n-1)!
    on factorial(n: Int) {
        // Base case
        if n <= 1 {
            return 1
        }
        // Recursive case: handler calls itself
        return n * factorial(n - 1)
    }

    // Fibonacci: fib(n) = fib(n-1) + fib(n-2)
    on fibonacci(n: Int) {
        if n <= 0 {
            return 0
        }
        if n == 1 {
            return 1
        }
        return fibonacci(n - 1) + fibonacci(n - 2)
    }

    // Sum of digits: 123 -> 1 + 2 + 3 = 6
    // Run: soma run 014_recursion.cell digit_sum 123
    // Expect: 6
    on digit_sum(n: Int) {
        if n < 10 {
            return n
        }
        return (n % 10) + digit_sum(n / 10)
    }
}