# with a subroutine reference that gets called to get the value
# of the scalar.  The sub will recieve the template object as a
# parameter.
$self->param(PARAM => sub { return 'value' });

##</code><code>##

$tmpl->param(
    blah => sub {
       my ($a, $b, $c) = @_; return 'something';
    } );

<tmpl_var name='blah(1,2,3)'>