If you enable debugging (DEBUG => 99),
you can see how Template compiles the templates (that
[% CALL list.pop %]
becomes
$stash->get(['list', 0, 'pop', 0]);, and [% list.pop %] becomes $output .= $stash->get(['list', 0, 'pop', 0]);).
MJDsays "you can't just make shit up and expect the computer to know what you mean, retardo!"