Turning nulls into zeroes, zeroes into empties

MonoidHomomorphism.scala

object MonoidHomomorphism extends App {

  import scalaz._
  import Scalaz._

  /**
   * Turn any null into the Zero value for its type
   */
  def nullAsZero[T: Monoid : Equal](a: T) = if (a == null) implicitly[Monoid[T]].zero else a

  /**
   * turn a Zero value of A into an empty M, or put a into an M
   */
  def zeroToEmpty[A : Equal: Monoid, M[_] : Applicative : PlusEmpty](a: A): M[A] =
    if (a.isMZero) PlusEmpty[M].empty else Applicative[M].point(a)

  /**
   * Turn null of T into empty M, or put a into M
   */
  def nullToEmpty[T: Monoid : Equal, M[_] : Applicative : PlusEmpty](a: T) = zeroToEmpty[T, M](nullAsZero(a))

  println(zeroToEmpty[String, Option]("")) // None
  println(zeroToEmpty[String, Option]("a")) // Some("a")
  val v: String = null
  println(nullToEmpty[String, Option](v)) // None

  println(zeroToEmpty[Int, List](0)) // Nil
  println(zeroToEmpty[Int, List](1)) // List(1)

}