my $foo; # Global, because this is the only visible (subroutine ref)

$foo=sub{
   print qq[First call - do first processing here \n];
   # First processing code goes here ...   
   
   # Now setup for subsequent calls .... 
  $foo=sub{
     print qq[subsequent calls\n]
     # Code for subsequent calls goes here
  }
};

$foo->() for 0..5; # OK - so the subroutine call looks slightly weird to newbies.