-- tail recursive definition of factorial, using a helper function
factorial_tail(n) = fac_helper(1,n)

fac_helper(p, 0) = p
fac_helper(p, n) = fac_helper(p*n, n-1)


-- simple recursive definition of factorial (can get inefficient for large n)
factorial(n) = 
	if n>0 then n*factorial(n-1)
	       else 1


main = print $ factorial_tail(15)