gistfile1.scala

scala> :paste
// Entering paste mode (ctrl-D to finish)

import shapeless._

trait Query[O] ; trait Query0[O] extends Query[O] ; trait Query1[I1, O] extends Query[O]
trait ActorRef[O]

trait Rel[-K, V]
object Rel {
  implicit def mkRel[O]: Rel[Query[O], ActorRef[O]] = new Rel[Query[O], ActorRef[O]] {}
}

val k0 = new Query0[Int] {}
val k1 = new Query1[String, Boolean] {}
val v0 = new ActorRef[Int] {}
val v1 = new ActorRef[Boolean] {}
val hm = HMap[Rel](k0 -> v0, k1 -> v1)

hm.get(k0)
hm.get(k1)

// Exiting paste mode, now interpreting.

import shapeless._
defined trait Query
defined trait Query0
defined trait Query1
defined trait ActorRef
defined trait Rel
defined object Rel
k0: Query0[Int] = $anon$1@20caecd0
k1: Query1[String,Boolean] = $anon$2@6a815c81
v0: ActorRef[Int] = $anon$3@52e04fc7
v1: ActorRef[Boolean] = $anon$4@495bc53
hm: shapeless.HMap[Rel] = shapeless.HMap@27eef7f
res0: Option[ActorRef[Boolean]] = Some($anon$4@495bc53)

scala> hm.get(k0)
res1: Option[ActorRef[Int]] = Some($anon$3@52e04fc7)

scala> hm.get(k1)
res2: Option[ActorRef[Boolean]] = Some($anon$4@495bc53)