package slib;

use enum qw(SM_UNK_REC
            SM_HDR_REC
            SM_TTL_REC);

   %SM_REC = ( SM_UNK_REC, "UNK",
               SM_HDR_REC, "HDR",
               SM_TTL_REC, "TTL" );

[...]

sub ABC {
   my ($type) = @_;

   if ($type == SM_HDR_REC) {
      [...]

   } elsif ($type == SM_TTL_REC) {
      [...]
}