gistfile1.scala

trait CPList {
  type Apply[A]
  type :+:[F[_]] <: CPList
  type Append[T <: CPList] <: CPList
}

trait NilCP[F[_]] extends CPList {
  type Apply[A] = F[A]
  type :+:[G[_]] = ConsCP[G,NilCP[F]]
  type Append[G <: CPList] = ConsCP[F, G]
}

trait ConsCP[H[_], T <: CPList] extends CPList {
  type Apply[A] = Coproduct[H, T#Apply, A]
  type :+:[F[_]] = ConsCP[F, ConsCP[H, T]]
  type Append[G <: CPList] = ConsCP[H, T#Append[G]]
}

type W[A] = (NilCP[Test1Algebra] # :+: [Test2Algebra] # :+: [Test3Algebra])#Apply[A]

implicit def F0: Functor[W] = Coproduct.coproductFunctor[Test3Algebra, ({ type l[a] = Coproduct[Test2Algebra, Test1Algebra, a] })#l]

// Does not compile, needs the right inject instance

/*
val res =
  for {
    a <- test1[W]("aa" :: Nil)
    b <- test2[W]("bb" :: Nil)
    c <- test3[W]("cc" :: Nil)
  } yield ()
*/