implicitly-either

implicitly-either.scala

scala> def implicitlyEitherImpl[A: c.TypeTag, B: c.TypeTag](c: reflect.makro.Context): c.Expr[Either[A, B]] = {
     |   def i[X](implicit X: c.TypeTag[X]): c.Tree = c.inferImplicitValue(X.tpe, silent = false)
     |   i[A] match {
     |     case c.mirror.EmptyTree =>
     |       i[B] match {
     |         case c.mirror.EmptyTree => 
     |           sys.error("Neither A nor B are available implicitly")
     |         case b =>
     |           c.reify(Right[A, B](c.Expr[B](b).eval))
     |         }
     |     case a => 
     |       i[B] match {
     |         case c.mirror.EmptyTree =>
     |           c.reify(Left[A, B](c.Expr[A](a).eval))
     |         case b =>
     |           sys.error("Both A and B are available implicitly")
     |       }
     |   }
     | }
implicitlyEitherImpl: [A, B](c: scala.reflect.makro.Context)(implicit evidence$1: c.TypeTag[A], implicit evidence$2: c.TypeTag[B])c.Expr[Either[A,B]]

scala> def implicitlyEither[A, B] = macro implicitlyEitherImpl[A, B]implicitlyEither: [A, B]=> Either[A,B]

scala> implicitlyEither[Int, Int]
<console>:14: error: exception during macro expansion: 
java.lang.RuntimeException: Neither A nor B are available implicitly
	at scala.sys.package$.error(package.scala:27)
	at .implicitlyEitherImpl(<console>:19)

              implicitlyEither[Int, Int]
                              ^

scala> implicitlyEither[Int, String]
<console>:14: error: exception during macro expansion: 
java.lang.RuntimeException: Neither A nor B are available implicitly
	at scala.sys.package$.error(package.scala:27)
	at .implicitlyEitherImpl(<console>:19)

              implicitlyEither[Int, String]
                              ^

scala> implicitlyEither[Int, Int => Int]
res15: Right[Int,Int => Int] = Right(<function1>)

scala> implicitlyEither[Int => Int, Int => Int]
<console>:14: error: exception during macro expansion: 
java.lang.RuntimeException: Both A and B are available implicitly
	at scala.sys.package$.error(package.scala:27)
	at .implicitlyEitherImpl(<console>:28)

              implicitlyEither[Int => Int, Int => Int]
                              ^

scala> implicitlyEither[Int => Int, Int]
res18: Left[Int => Int,Int] = Left(<function1>)