dslSyntaxExample.scala

   val endpoint0 = handle(
        fromJson[PartialRequestMessage].body and from(req ⇒ 'name ->> req.headers("my_name") :: HNil),
        process[RequestMessage] using myActor `then` expect[ResponseMessage].respondJson(Ok(_))
      )
   
   val endPoint1 = handleParams(
        process[RequestMessage] using myActor `then` expect[ResponseMessage].respond(Ok) `with` authentication
      )
   
   
   val endPoint2 = handle(
        fromAuthorized(SessionInfo)(si ⇒ 'id ->> si.sessionId :: HNil),
        process[RequestMessage] using myActor `then` expect[ResponseMessage].respondJson(Ok(_))
      )
      
    val endPoint3 = handleParams(
      process[RequestMessage] using myActor `then`
      expect[ProcessResult].respondJson(Ok(_)).ifEmpty(_.content).respond(NotFound)
    )
    
    val endpoint = handleParams(
      `with`(caching(3.hours) and authentication) {
        process[RequestMsg] using actor `then`
          (expect[ResponseMsg] respondJson (Ok(_)) `with` eTag(_.updated))
      }
    )

    

on a different note, having the users construct HLists would mean they'd have to include Shapeless in their codebase (include the library, add the necessary imports, etc) independent from the play-dsl library. or maybe that's not such a big deal.

I wonder if there's a way to have the from method to have an alternate version that accepts a function Request => Tuple (of arbitrary size) and convert that to an HList. This way they could use built-in scala features to call it.

e.g.,

from(req => ('name -> req.headers("my_name"), 'somethingElse -> req.headers("abc"))

where each element in the tuple is of type (Symbol, T), which then gets converted to a record HList inside the play-dsl library. Not sure how much effort that would require (particularly, the part about from accepting a tuple of arbitrary size/types)

both authentication and eTag are Filters which is
type Filter[-RMT] = (Request[RMT], ⇒ Future[Result]) ⇒ Future[Result]

The type (Symbol, T) doens't translate the value of the symbol into the type information, i.e. ('name, 1) and ('age, 2) are exactly the same type. I think the ->> constructor from shapeless manage to convert the value of symbol into a singleton type. So I am not sure if it is achievable through the tuple values you suggested.