diff --git a/util/collection/HList.scala b/util/collection/HList.scala
index db2c9db85..df0391de8 100644
--- a/util/collection/HList.scala
+++ b/util/collection/HList.scala
@@ -13,12 +13,16 @@ sealed trait HNil extends HList
 {
 	type Wrap[M[_]] = HNil
 	def :+: [G](g: G): G :+: HNil = HCons(g, this)
+
+	override def toString = "HNil"
 }
 object HNil extends HNil
 final case class HCons[H, T <: HList](head : H, tail : T) extends HList
 {
 	type Wrap[M[_]] = M[H] :+: T#Wrap[M]
 	def :+: [G](g: G): G :+: H :+: T = HCons(g, this)
+
+	override def toString = head + " :+: " + tail.toString
 }
 
 object HList
diff --git a/util/collection/KList.scala b/util/collection/KList.scala
index 81ef6afcd..aa9662917 100644
--- a/util/collection/KList.scala
+++ b/util/collection/KList.scala
@@ -31,6 +31,8 @@ final case class KCons[H, T <: HList, +M[_]](head: M[H], tail: KList[M,T]) exten
 	def toList = head :: tail.toList
 	
 	def combine[N[X] >: M[X]]: (H :+: T)#Wrap[N] = HCons(head, tail.combine)
+
+	override def toString = head + " :^: " + tail.toString
 }
 
 sealed class KNil extends KList[Nothing, HNil]
@@ -40,6 +42,7 @@ sealed class KNil extends KList[Nothing, HNil]
 	def :^: [M[_], H](h: M[H]) = KCons(h, this)
 	def toList = Nil
 	def combine[N[X]] = HNil
+	override def toString = "KNil"
 }
 object KNil extends KNil