title: akka-http implicit json format for list of case classes
body: <p>i want ro make a response</p>
  <pre><code>val res: List[Categories] = CategoryObj.getCategories
  complete(OK, res)
  </code></pre>
  <p>i wrote an implicit json formats</p>
  <pre><code>implicit val jsCat = jsonFormat3(Category)
  implicit val jsCats = jsonFormat1(Seq[Category])
  </code></pre>
  <p>but for a second line i got three errors</p>
  <blockquote>
  <p>Error:(8, 25) inferred type arguments
  [Seq[DAO.Category],Seq[DAO.Category]] do not conform to method
  jsonFormat1's type parameter bounds [P1,T &lt;: Product]   implicit val
  jsCats = jsonFormat1(Seq[Category])</p>
  <p>Error:(8, 40) type mismatch;  found   : Seq[DAO.Category] =&gt;
  Seq[DAO.Category]  required: P1 =&gt; T  Note: implicit value jsCats is
  not applicable here because it comes after the application point and
  it lacks an explicit result type   implicit val jsCats =
  jsonFormat1(Seq[Category])</p>
  <p>Error:(8, 36) could not find implicit value for evidence parameter of
  type spray.json.DefaultJsonProtocol.JF[P1] (Cannot find JsonWriter or
  JsonFormat type class for P1)   implicit val jsCats =
  jsonFormat1(Seq[Category])</p>
  </blockquote>
  <p>And i can't get how to deal with them</p>