Definitions

   The factorial of   0   (zero)   is defined as being   1   (unity).
   The   Factorial Function   of a positive integer,    n,    is defined as the product of the sequence:
                 n,   n-1,   n-2,   ...   1 



Task

Write a function to return the factorial of a number.

Solutions can be iterative or recursive.

Support for trapping negative    n    errors is optional.



Related task

   Primorial numbers


beads 1 program Factorial
//  only works for cardinal numbers 0..N
calc main_init
	log to_str(Iterative(4))  //  24
	log to_str(Recursive(5))  //  120
 
calc Iterative(
	n:num	--  number of iterations
	):num   --  result
	var total = 1
	loop from:2 to:n index:ix
		total = ix * total 
	return total
 
calc Recursive ditto
	if n <= 1
		return 1
	else
		return n * Recursive(n-1)