build.sbt

scalaVersion := "2.11.2"

libraryDependencies += "com.chuusai" %% "shapeless" % "2.0.0"

name := "Observe Sample"

unwrap.scala

trait Obs[A, B] { def value: A }
trait ChildObs[A, B] extends Obs[A, B]

object Obs {
  import shapeless._, poly._, ops.hlist.Mapper, ops.function.FnToProduct

  object values extends Poly1 {
    implicit def a1[A, X, C <: Obs[A,X]] = at[C]{ _.value }
    implicit def a2[A, X]                = at[Obs[A,X]]{ _.value }
    implicit def a3[A, C <: Obs[A, _]]   = at[C]{ _.value }
  }

  def calculate[T, V <: HList, L <: HList, F, Z](obss: T)(f: F)(implicit
    gen: Generic.Aux[T, L],
    mapper: Mapper.Aux[values.type, L, V],
    ftp: FnToProduct.Aux[F, V => Z]
  ): Z = ftp(f)(mapper.apply(gen.to(obss)))
}

object ObsExample {
  import Obs._

  val obs1: Obs[Double, Double] = new ChildObs[Double, Double] { val value = 10.0 }
  val obs2: ChildObs[Option[Int], Int] = new ChildObs[Option[Int], Int] { val value = Some(1) }

  def func(d: Double, i: Option[Int]) = d + i.getOrElse(0).toDouble

  println(calculate(obs1, obs2)(func _))
}