sub default_handler {
    print OUT "@@@ main::$_[0](\$tree) @@@\n";
    recurse($_[1]);
}

sub dispatch {
    ref $_[0] eq 'ARRAY' ? \&startrule :
        $main::{$_[0]} || \&default_handler;
}

sub startrule {
    my $tree = shift;
    ref eq 'ARRAY' and dispatch($_->[0])->($_) foreach @$tree;
}