use strict;
use warnings;

my $count = 0;
my $max_output = 7;

sub rec {
  my $hash  = shift;
  my $level = shift;
  return if $level > 1;

  while ( my ( $k, $v ) = each %$hash ) {
    exit 0 if ++$count > $max_output;   # backstop
    print "$level: $k\n";
    rec( $hash, $level + 1 );
  }
}

rec( { foo => 1, bar => 2, baz => 3 }, 0 );

__END__
0: bar
1: baz
1: foo
0: bar
1: baz
1: foo
0: bar