my $call=0;
 
sub generator (;$) {
  my $inner_iter=shift;
  my $dummy;
  
  $outer_iter=sub {};
  # $outer_iter=sub { $inner_iter->() };
  # $outer_iter=sub { $dummy++ };
  $call++;
  
  print "Call Nr $call\n";
  
  if ($inner_iter){
    print $inner_iter."\n";
    if ( $inner_iter eq $outer_iter) {
      print "ERROR !!!\n"
    }
  }
  
  return $outer_iter;
}
 
print generator generator;

##</code><code>##

/usr/bin/perl -w /tmp/tst.pl 
Call Nr 1
Call Nr 2
CODE(0x90fa080)
ERROR !!!
CODE(0x90fa080)

##</code><code>##

Call Nr 1
Call Nr 2
CODE(0x9604880)
CODE(0x9623210)

##</code><code>##

sub gen_arr {
  my $inner_arr=shift;
  
  print my $outer_arr=[];
  
  return $outer_arr;
}

gen_arr gen_arr;

#prints ARRAY(0xa179880)ARRAY(0xa179760)