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-rw-r--r--tests/pos/t1513a.scala36
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diff --git a/tests/pos/t1513a.scala b/tests/pos/t1513a.scala
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+object Test {
+ // Heterogeneous lists and natural numbers as defined in shapeless.
+
+ sealed trait HList
+ sealed trait ::[H, T <: HList] extends HList
+ sealed trait HNil extends HList
+
+ sealed trait Nat
+ sealed trait Succ[P <: Nat] extends Nat
+ sealed trait Zero extends Nat
+
+ // Accessor type class to compute the N'th element of an HList L.
+
+ trait Accessor[L <: HList, N <: Nat] { type Out }
+ object Accessor {
+ type Aux[L <: HList, N <: Nat, O] = Accessor[L, N] { type Out = O }
+
+ // (H :: T).At[Zero] = H
+ implicit def caseZero[H, T <: HList]: Aux[H :: T, Zero, H] = ???
+
+ // T.At[N] = O => (H :: T).At[Succ[N]] = O
+ implicit def caseN[H, T <: HList, N <: Nat, O]
+ (implicit a: Aux[T, N, O]): Aux[H :: T, Succ[N], O] = ???
+ }
+
+ case class Proxy[T]()
+
+ def at1[NN <: Nat, OO] (implicit e: Accessor.Aux[String :: HNil, NN, OO]): OO = ???
+ def at2[NN <: Nat, OO](p: Proxy[NN])(implicit e: Accessor.Aux[String :: HNil, NN, OO]): OO = ???
+
+ // N is fixed by a value
+ at2(Proxy[Zero]): String
+
+ // N is fixed as a type parameter (by name)
+ at1[NN = Zero]: String
+}