Finally, we bake our cake and enjoy:
object BookApi extends Endpoints with Sources with JsonRules
import scala.concurrent.ExecutionContext.Implicits.global
val book: Future[Book] = BookApi.needBook("book-1").go // hurray!
The example is not complete w.r.t. all the optimizations claimed in the introduction. But come on, it even deals with a fictional web service. For a better idea on how things work, head to the guide. If you are specifically interested in how to do this or that, check out the recipes section.