use Data::Dumper;
use constant MSG_DATA => { foo => 1 },
                         { bar => 2 },
                         { baz => 3 };

for my $msg (MSG_DATA) {
    print Dumper $msg;
}

##</code><code>##

use constant FOO => "xyz",
             BAR => "def",
             BAZ => "abc";

# FOO returns qw/xyz BAR def BAZ abc/
# BAR and BAZ aren't defined as constants

##</code><code>##

use constant { FOO => "xyz",
               BAR => "def",
               BAZ => "abc" };