An implicit conversion that itself requires another implicit conversion.

ImplicitRecursion.scala

object ImplicitRecursion {
  abstract class Nat
  class Zero extends Nat 
  class Succ[T <: Nat] extends Nat 
  type _0 = Zero
  type _1 = Succ[_0]
  type _2 = Succ[_1]
  type _3 = Succ[_2]
  type _4 = Succ[_3]
  type _5 = Succ[_4]
  type _6 = Succ[_5]
  type _7 = Succ[_6]
  type _8 = Succ[_7]
  type _9 = Succ[_8]
  implicit def SuccToN[T <: Nat](value: Succ[T])(implicit rec: T => Int): Int = rec(null.asInstanceOf[T]) + 1
  implicit def ZeroTo0[T <: Nat](zero: T): Int = 0
  def nat2Int[T <: Nat](implicit tr: T => Int): Int = tr(null.asInstanceOf[T])
}
import ImplicitRecursion._
println(nat2Int[_8])