$some_var = 'Hello world!';
$my_templ->process( "$TEMPLATE_DIR/hello_world.html",
                    { 'filler' => \&some_sub( $some_var ) } );

##</code><code>##

$some_var = &some_sub( 'Hello world!' );
$my_templ->process( "$TEMPLATE_DIR/hello_world.html",
                    { 'filler' => $some_var } );