$ perl driver.pl
function 'heights_agl' already defined, overrides struct accessor method at Lib/Datum.pm line 8.
Odd number of elements in hash assignment at Lib/Datum.pm line 25.
$VAR1 = [
          'Variable',
          'heights_agl',
          []
        ];
$ perl -v

This is perl 5, version 26, subversion 1 (v5.26.1) built for x86_64-linux-gnu-thread-multi
(with 67 registered patches, see perl -V for more detail)