Add AreElementsOf

core/src/main/scala/zio/constraintless/AreElementsOf.scala

@@ -0,0 +1,36 @@
+package zio.constraintless
+
+import TypeList.{::, End}
+
+sealed trait AreElementsOf[T1 <: TypeList, T2 <: TypeList]
+
+object AreElementsOf {
+  def apply[T1 <: TypeList, T2 <: TypeList](implicit
+      ev: AreElementsOf[T1, T2]
+  ): AreElementsOf[T1, T2] = ev
+
+  final case class TypeCollection[T1, T11 <: TypeList, T2 <: TypeList](
+      ev1: T1 IsElementOf T2,
+      ev2: T11 AreElementsOf T2
+  ) extends AreElementsOf[T1 :: T11, T2]
+
+  final case class NilCollection[T2 <: TypeList]()
+      extends AreElementsOf[End, T2]
+
+  implicit def typesElementsOfTypes[Head, Tail <: TypeList, Types <: TypeList](
+      implicit
+      ev1: Head IsElementOf Types,
+      ev2: Tail AreElementsOf Types
+  ): AreElementsOf[Head :: Tail, Types] =
+    TypeCollection(ev1, ev2)
+
+  implicit def endElementOfTypes[Types <: TypeList]: AreElementsOf[End, Types] =
+    NilCollection()
+
+}
+
+object Sample extends App {
+  println(AreElementsOf[Int :: Double :: End, Int :: Double :: End])
+  println(AreElementsOf[Double :: Int :: End, Int :: Double :: Long :: End])
+  // println(AreElementsOf[String :: Double :: End, Int :: Double :: End]) // doesn't compiol;e
+}

core/src/main/scala/zio/constraintless/IsElementOf.scala

@@ -4,7 +4,6 @@ import TypeList._
 
 sealed trait IsElementOf[Type, Types <: TypeList]
 
-//
 object IsElementOf {
   def apply[A, As <: TypeList](implicit
       ev: IsElementOf[A, As]

examples/src/main/scala/zio/constraintless/examples/Expr.scala

@@ -17,7 +17,6 @@ case class Prod[As <: TypeList, A, B](
     b: Expr[As, B],
     c1: A IsElementOf As,
     c2: B IsElementOf As,
-    c3: (A, B) IsElementOf As
 ) extends Expr[As, (A, B)]
 
 case class Cond[As <: TypeList, A](