Merge pull request scala#4389 from retronym/topic/jesper

Resurrect a test for type inference

Author: retronym

test/files/pos/jesper.scala

@@ -0,0 +1,30 @@
+object Pair {
+ sealed trait Pair {
+   type First
+   type Second <: Pair
+ }
+
+ case class End() extends Pair {
+   type First = Nothing
+   type Second = End
+
+   def ::[T](v : T) : Cons[T, End] = Cons(v, this)
+ }
+
+ object End extends End()
+
+ final case class Cons[T1, T2 <: Pair](_1 : T1, _2 : T2) extends Pair {
+   type First = T1
+   type Second = T2
+
+   def ::[T](v : T) : Cons[T, Cons[T1, T2]] = Cons(v, this)
+   def find[T](implicit finder : Cons[T1, T2] => T) = finder(this)
+ }
+
+ implicit def findFirst[T1, T2 <: Pair] : Cons[T1, T2] => T1 = (p : Cons[T1, T2]) => p._1
+ implicit def findSecond[T, T1, T2 <: Pair](implicit finder : T2 => T) : Cons[T1, T2] => T = (p : Cons[T1, T2]) => finder(p._2)
+
+ val p : Cons[Int, Cons[Boolean, End]] = 10 :: false :: End
+// val x : Boolean = p.find[Boolean](findSecond(findFirst))
+ val x2 : Boolean = p.find[Boolean]  // Doesn't compile
+}