use strict;
use warnings;

package Logger;

use Exporter qw( import );

our @EXPORT_OK = qw(
   LOG_ERROR
   LOG_VERBOSE_ERROR
   LOG_WARNING
   LOG_VERBOSE_WARNING
   output
);

our %EXPORT_TAGS = (
   err_levels => [qw(
      LOG_ERROR
      LOG_VERBOSE_ERROR
      LOG_WARNING
      LOG_VERBOSE_WARNING
   )],
);

use constant {
   LOG_ERROR   => 1,
   LOG_WARNING => 2,
};

use constant {
   LOG_VERBOSE_ERROR   => -LOG_ERROR,
   LOG_VERBOSE_WARNING => -LOG_WARNING,
};

sub output {
   ...
}

1;