an><hr class="error-divider"><div class="listed-error"><div class="error-line">Cannot find name 'preprocess'.</div></div><div class="listed-error"><div class="error-line">'}' expected.</div></div><a class="playground-link" href="https://www.typescriptlang.org/play/#src=type%20Thing%20%3D%20%7B%20name%3A%20'one'%20%7C%20'two'%20%7D%3B%0Afunction%20process(origin%3A%20Thing%2C%20extra%3F%3A%20Thing%20%7C%20undefined)%3A%20void%20%7B%0A%20%20preprocess(origin%2C%20extra)%3B%0A%20%20if%20(extra)%20%7B%0A%20%20%