zero.scala

trait Zero[+A] {
  val zero: A
}

implicit object IntZero extends Zero[Int] {
  val zero = 0
}

implicit def ListZero[A](implicit ev: Zero[A]) =
  new Zero[List[A]] { val zero = Nil }

// utility
def optional[A](a: A)(implicit ev: Zero[A]) =
  if(a == ev.zero) None else Some(a)

// pimp
class ZeroPimp[A](a:A)(implicit ev: Zero[A]) {
  def optional(implicit ev: Zero[A]) =
    if(a == ev.zero) None else Some(a)
}
implicit def zp[A](a: A)(implicit ev: Zero[A]) = new ZeroPimp(a)

/*
scala> 0.optional
res9: Option[Int] = None

scala> 1.optional
res10: Option[Int] = Some(1)

scala> Nil.optional
<console>:21: error: could not find implicit value for parameter ev: Zero[object Nil]
       Nil.optional
       ^

scala> List(0).optional
res12: Option[List[Int]] = Some(List(0))

scala> List[Int]().optional
res13: Option[List[Int]] = None
 */