error

def lessonDelta[M]
  (sm: ServiceModel[M], uid: UserId, courseKey: String)
  (delta: IndexedSeq[Lesson] => ModelState[M, IndexedSeq[Lesson]]): ModelState[M, Unit] =
    for {
      courseId             <- sm.findCourseId(courseKey)
      _                    <- sm.asAuthor(uid, courseId)
      oldStatus            <- sm.getSandboxStatusById(courseId)
      courseToUpdate       <- sm.sandboxedCourse(courseId, oldStatus)
      oldPalette           <- sm.getGadgetPalette(courseId, Course.SANDBOX)
      // this line is failing:
      changedLessons       <- delta(courseToUpdate.lessons)
      newPalette           <- CourseParser.derivePalette(sm, oldPalette, changedLessons)
      updatedSandboxCourse <- courseToUpdate.updateLessons(changedLessons)
      updatedSandboxStatus  =
        SandboxChanges.validate(updatedSandboxCourse, sm.stagedStatus(oldStatus))
      _                    <- sm.mc.setSandboxStatus(courseId, updatedSandboxStatus)
      _                    <- sm.mc.setGadgetPalette(courseId, Course.SANDBOX, newPalette)
    } yield ()
    

//[error] /Users/kelleyrobinson/src/rest-api/src/main/scala/endpoints/CourseEndpoints.scala:774: 
// Unable to unapply type `com.versal.restapi.Course` into a type constructor of kind `M[_]` 
// that is classified by the type class `scalaz.Functor`
//[error] 1) Check that the type class is defined by compiling `implicitly[scalaz.Functor[<type constructor>]]`.
//[error] 2) Review the implicits in object Unapply, which only cover common type 'shapes'
//[error] (implicit not found: scalaz.Unapply[scalaz.Functor, com.versal.restapi.Course])
//[error]       updatedSandboxCourse <- courseToUpdate.updateLessons(changedLessons)