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if (template address exists) {
    include template
} else {
    include other template
}

sub template_exists {
    my ($self, $file) = @_;
    my $path = $self->config->template_path;
    return 1 if grep { -e && -f && -r } map { "$_/$file" } @$path;
    return;
}

[% FOREACH thing = collection %]
    [% template = factory.template_exists("list/types/${thing.type}.ht
+ml") ?
...
    %]
    [% INCLUDE $template %]
[% END %]