function stringDriver(sink: Stream<string>) {
   return xs.of('b');
 }

 function driver(sink: Stream<string>) {
   return xs.of('b').debug(spy);
 }

 function main(sources: {history: Stream<Location>}) {
   return {
     history: xs.of({type: 'replace', pathname: '/test'}),
   };
 }

 .map(x => (x === 1 ? xs.of(div()) : child.DOM))

 function app(sources: {DOM: MainDOMSource}) {
   const vtree$ = xs.of(h3('.top-most'));
   return {
     DOM: sources.DOM.isolateSink(vtree$, 'foo'),
   };
 }

 function app(_sources: {DOM: MainDOMSource}) {
   return {
     DOM: xs.of(div()),
   };
 }

 function app(sources: {DOM: MainDOMSource}) {
   return {
     DOM: xs.of(h3('.myelementclass', 'Foobar')),
   };
 }

 function app2() {
   return {second: xs.of('test')};
 }

 drv: (s: Stream<string | number>) => xs.of('foo'),