service.scala

// RegistrationFormValidator.validateForm(form) returns Either[ValidationError, ValidRegistration]
// the expected return type of our HttpService[F] creator is F[Response[F]], so here we use .bimap
// and friends to finagle our validated form into that type.

val service: HttpService[F] = {
    HttpService[F] {
      case req @ POST -> Root / "users" =>
        req.decode[RegistrationForm] { form =>
          RegistrationFormValidator.validateForm(form).bimap(error => registrationFailed(error),
              user => insertRegistration(User(UUID.randomUUID, user.email, user.password.bcrypt))
                .map(registrationSucceeded).flatMap(identity)).merge
        }
    }
}