% ./tst.pl 
Start with 0
-> Subcall with 1
 Start with 1
 -> Subcall with 2
  Start with 2
  -> Subcall with 3
   Start with 3
   At 3, returning.
  <- Back from 3
  Done with 2
 <- Back from 2
 Done with 1
<- Back from 1
Done with 0