Lazy, labels, and scalaz.@@

TC compile_output.txt

[info] Compiling 2 Scala sources to /Users/alexandre/projects/shapeless/examples/target/scala-2.11/classes...
[error] /Users/alexandre/projects/shapeless/examples/src/main/scala/shapeless/examples/TCTag.scala:66: could not find implicit value for parameter e: shapeless.examples.TC[shapeless.examples.TestScalazTag.R]
[error]   implicitly[TC[R]] // ...but not for its record
[error]             ^
[error] /Users/alexandre/projects/shapeless/examples/src/main/scala/shapeless/examples/TCTag.scala:68: could not find implicit value for parameter e: shapeless.examples.TC[shapeless.examples.DummyTagged]
[error]   implicitly[TC[DummyTagged]] // Does *not* work for this one...
[error]             ^
[error] /Users/alexandre/projects/shapeless/examples/src/main/scala/shapeless/examples/TCTag.scala:73: could not find implicit value for parameter e: shapeless.examples.TC[shapeless.examples.TestScalazTag.RT]
[error]   implicitly[TC[RT]] // ...nor for its record
[error]             ^
[error] three errors found
[error] (shapeless-examples/compile:compile) Compilation failed
[error] Total time: 2 s, completed 11 janv. 2015 23:24:07

TC NonLabelled.scala

package shapeless
package examples

import scalaz.@@
import labelled._
import record._

trait TC[T] {
  def apply(): String
}

trait CustomTag

object TC {
  implicit val intTC: TC[Int] =
    new TC[Int] {
      def apply() = "Int"
    }

  implicit val booleanTC: TC[Boolean] =
    new TC[Boolean] {
      def apply() = "Boolean"
    }

  implicit val taggedIntTC: TC[Int @@ CustomTag] =
    new TC[Int @@ CustomTag] {
      def apply() = s"TaggedInt"
    }

  implicit val hnilTC: TC[HNil] =
    new TC[HNil] {
      def apply() = "HNil"
    }

  implicit def hconsTC[H, T <: HList](implicit
    headTC: Lazy[TC[H]],
    tailTC: Lazy[TC[T]]
  ): TC[H :: T] =
    new TC[H :: T] {
      def apply() = s"${headTC.value()} :: ${tailTC.value()}"
    }

  implicit def projectTC[F, G](implicit
    gen: Generic.Aux[F, G],
    tc: Lazy[TC[G]]
  ): TC[F] =
    new TC[F] {
      def apply() = s"Proj(${tc.value()})"
    }
}

case class Dummy(i: Int @@ CustomTag)
case class DummyTagged(b: Boolean, i: Int @@ CustomTag)

object TestScalazTag {
  implicitly[TC[Int @@ CustomTag]]
  implicitly[TC[Boolean]]


  implicitly[TC[Dummy]] // All works here

  type L = HList.`Int @@ CustomTag`.T
  val gen = Generic[Dummy]
  implicitly[gen.Repr =:= L]
  implicitly[TC[L]]

  implicitly[TC[DummyTagged]]

  type LT = HList.`Boolean, Int @@ CustomTag`.T
  val gent = Generic[DummyTagged]
  implicitly[gent.Repr =:= LT]
  implicitly[TC[LT]]
}

TC.scala

package shapeless
package examples

import scalaz.@@
import labelled._
import record._

trait TC[T] {
  def apply(): String
}

trait CustomTag

object TC {
  implicit val intTC: TC[Int] =
    new TC[Int] {
      def apply() = "Int"
    }

  implicit val booleanTC: TC[Boolean] =
    new TC[Boolean] {
      def apply() = "Boolean"
    }

  implicit val taggedIntTC: TC[Int @@ CustomTag] =
    new TC[Int @@ CustomTag] {
      def apply() = s"TaggedInt"
    }

  implicit val hnilTC: TC[HNil] =
    new TC[HNil] {
      def apply() = "HNil"
    }

  implicit def hconsTC[K <: Symbol, H, T <: HList](implicit
    key: Witness.Aux[K],
    headTC: Lazy[TC[H]],
    tailTC: Lazy[TC[T]]
  ): TC[FieldType[K, H] :: T] =
    new TC[FieldType[K, H] :: T] {
      def apply() = s"${key.value.name}: ${headTC.value()} :: ${tailTC.value()}"
    }

  implicit def projectTC[F, G](implicit
    lgen: LabelledGeneric.Aux[F, G],
    tc: Lazy[TC[G]]
  ): TC[F] =
    new TC[F] {
      def apply() = s"Proj(${tc.value()})"
    }
}

case class Dummy(i: Int @@ CustomTag)
case class DummyTagged(b: Boolean, i: Int @@ CustomTag)

object TestScalazTag {
  implicitly[TC[Int @@ CustomTag]]
  implicitly[TC[Boolean]]


  implicitly[TC[Dummy]] // Works for this one...

  type R = Record.`'i -> Int @@ CustomTag`.T
  val lgen = LabelledGeneric[Dummy]
  implicitly[lgen.Repr =:= R]
  implicitly[TC[R]] // ...but not for its record

  implicitly[TC[DummyTagged]] // Does *not* work for this one...

  type RT = Record.`'b -> Boolean, 'i -> Int @@ CustomTag`.T
  val lgent = LabelledGeneric[DummyTagged]
  implicitly[lgent.Repr =:= RT]
  implicitly[TC[RT]] // ...nor for its record
}