missingSomething.js

// File: /packages/my-first-theme/src/components/index.js

// ...
import Post from "./post"

const Root = ({ state }) => {
  const data = state.source.get(state.router.link)

  return (
    <>
      {/* ... */}
      <Switch>
        <List when={data.isArchive} />
        <Post when={data.isPost} />
        <Post when={data.isPage} />
      </Switch>
    </>
  )
}