Existentially abstract unbound subtype parameters

That happens when the subtype of a sealed trait has more type
parameters than its parent. When those extra type parameters are
covariant they are replaced by their upper bounds, otherwise they
are existentially quantified.

1 files changed, 6 insertions, 0 deletions

diff --git a/examples/shared/src/main/scala/show.scala b/examples/shared/src/main/scala/show.scala
index 50b34ee..9f634ba 100644
--- a/examples/shared/src/main/scala/show.scala
+++ b/examples/shared/src/main/scala/show.scala
@@ -60,4 +60,10 @@ object Show extends GenericShow[String] {
   implicit val int: Show[String, Int] = new Show[String, Int] {
     def show(s: Int): String = s.toString
   }
+
+  /** show typeclass for sequences */
+  implicit def seq[A](implicit A: Show[String, A]): Show[String, Seq[A]] =
+    new Show[String, Seq[A]] {
+      def show(as: Seq[A]): String = as.iterator.map(A.show).mkString("[", ",", "]")
+    }
 }