.raiseError syntax allows an error subtype

typelevel · Sep 18, 2018 · bdf9f9e · bdf9f9e
1 parent 1911e8b
commit bdf9f9e
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diff --git a/core/src/main/scala/cats/syntax/applicativeError.scala b/core/src/main/scala/cats/syntax/applicativeError.scala
@@ -67,7 +67,7 @@ final class ApplicativeErrorExtensionOps[F[_], E](F: ApplicativeError[F, E]) {
 }
 
 final class ApplicativeErrorIdOps[E](val e: E) extends AnyVal {
-  def raiseError[F[_], A](implicit F: ApplicativeError[F, E]): F[A] =
+  def raiseError[F[_], A](implicit F: ApplicativeError[F, _ >: E]): F[A] =
     F.raiseError(e)
 }
 

diff --git a/tests/src/test/scala/cats/tests/ApplicativeErrorSuite.scala b/tests/src/test/scala/cats/tests/ApplicativeErrorSuite.scala
@@ -62,4 +62,33 @@ class ApplicativeErrorSuite extends CatsSuite {
       (().raiseError[OptionWrapper, Int] orElse OptionWrapper(17.some)).option should === (OptionWrapper(17.some).option)
     }
   }
+
+  {
+    trait Super
+    case object Sub extends Super
+
+    final case class EitherWrapper[A](either: Either[Super, A])
+
+    implicit val EitherWrapperApplicativeError: ApplicativeError[EitherWrapper, Super] = {
+      val ev = ApplicativeError[Either[Super, ?], Super]
+      new ApplicativeError[EitherWrapper, Super] {
+
+        def raiseError[A](e: Super): EitherWrapper[A] =
+          EitherWrapper(ev.raiseError(e))
+
+        def handleErrorWith[A](fa: EitherWrapper[A])(f: Super => EitherWrapper[A]): EitherWrapper[A] =
+          EitherWrapper(ev.handleErrorWith(fa.either)(f(_).either))
+
+        def pure[A](x: A): EitherWrapper[A] =
+          EitherWrapper(x.asRight)
+
+        def ap[A, B](ff: EitherWrapper[A => B])(fa: EitherWrapper[A]): EitherWrapper[B] =
+          EitherWrapper(ev.ap(ff.either)(fa.either))
+      }
+    }
+
+    test("raiseError syntax allows an error subtype") {
+      assert(Sub.raiseError[EitherWrapper, Unit].either.isLeft)
+    }
+  }
 }