use strict;
use warnings;
use constant FOO => 10; 
use constant BAR => 20; 
use Data::Dump qw/ dump /;

my %BAZ = ( 
    FOO() => 1,
    BAR() => 1
);

my %BOO = ( 
    FOO => 1,
    BAR => 1
);

my %BAH = FOO => 1, BAR => 1;

print 'BAZ: ' . dump(\%BAZ) . "\n";
print 'BOO: ' . dump(\%BOO) . "\n";
print 'BAH: ' . dump(\%BAH) . "\n";