Scala NList

gistfile1.scala

package nlist                                                                   

sealed trait Nat 
sealed trait Z extends Nat 
sealed trait S[A <: Nat] extends Nat 

sealed trait NList[A <: Nat, +B] {
  type Length = A 

  def zap[C](l: NList[Length, B => C]): NList[Length, C]
}

case object NNil extends NList[Z, Nothing] {
  def zap[A](l: NList[Length, Nothing => A]): NNil.type = 
    NNil
}

sealed case class NCons[A <: Nat, B](head: B, tail: NList[A, B])
extends NList[S[A], B] {

  def zap[C](l: NList[Length, B => C]): NList[Length, C] = 
    l match {
      case NCons(f, fs) =>  
        NCons(f(head), tail zap fs) 
    }   
}