Basic scala list-like implementation.

ListyMain.scala

object Main {
  type T = Any
  trait Listy[T] {
    val value: T
    def isEmpty: Boolean
    def head: Option[T]
    def tail: Listy[T]
    def filter(predicate: T => Boolean): Listy[T] = {
      if (predicate(value)) ListyImpl(value, tail.filter(predicate)) else tail
    }
    def find(predicate: T => Boolean): Option[T] = {
      if (predicate(value)) Some(value) else {
        if (tail.isEmpty) None
        else tail.find(predicate)
      }
    }
    implicit def ::(value: T): Listy[T] = ListyImpl(value, if (tail.isEmpty) Nily else tail)
  }
  case object Nily extends Listy[T] {
    val value = null
    def isEmpty = true
    def head = throw new java.util.NoSuchElementException("head of an empty list")
    def tail = throw new UnsupportedOperationException("tail of an empty list")
  }

  case class ListyImpl[T](value: T, rest: Listy[T]) extends Listy[T] {
    def isEmpty = false
    def head = Some(value)
    def tail = rest
  }

  def main(args: Array[String]): Unit = {
    // convert to list using single operator.
    val list = 1 :: Nily
  }
}