$ perl demo.pl 
hello from 1
hello from 2
hello from 3
hello from 4
3: 2 * 2 = 4
4: 1 * 2 = 2
2: 3 * 2 = 6
3: 5 * 2 = 10
4: 6 * 2 = 12
1: 4 * 2 = 8
4: 7 * 2 = 14
3: 8 * 2 = 16
2: 9 * 2 = 18
1: 10 * 2 = 20
10792 0 Hello 0  one
10793 0 There 0  two
10794 0 foo 0  something from 10794
10795 0 baz 0  something from 10795
fib(20) = 6765