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| // add scalacOptions += "-Ypartial-unification" to build.sbt | |
| import scala.reflect.runtime._, universe._ | |
| import scala.language.higherKinds | |
| def checkUnification[F[_], A: TypeTag](fa: => F[A]) = s"${typeOf[A]}" | |
| assert(checkUnification(e) == "String") | |
| assert(checkUnification(f) == "List[Int]") | |
| implicit class InferToLeft[M[_, _], A, B](a: M[A, B]) { | |
| def lefty: InferToLeft.U[M, B, A] = a | |
| } | |
| object InferToLeft { | |
| type U[M[_, _], B, A] = M[A, B] | |
| } | |
| def e: Either[Int, String] = ??? | |
| def f: AnyRef => List[Int] = ??? | |
| assert(checkUnification(e.lefty) == "Int") | |
| assert(checkUnification(f.lefty) == "AnyRef") |
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