List's span variations

ListSpanVariations.scala

import scala.collection.mutable.ListBuffer

/**
 * Span-like inclusive methods for slicing list based on element predicates.
 * @author Vasco Figueira
 * @author Peter Empen 
 */
class ListSpanVariations[A](l: List[A]) {

  /**
   * Original span implementation
   */
  def span(p: A => Boolean): (List[A], List[A]) = {
    val b = new ListBuffer[A]
    var these = l
    while (!these.isEmpty && p(these.head)) {
      b += these.head
      these = these.tail
    }
    (b.toList, these)
  }

  /**
   * Like span in List but including the first element for which
   * p is false
   *
   * Adds one extra var
   */
  def spanInclusive(p: A => Boolean): (List[A], List[A]) = {
    val b = new ListBuffer[A]
    var these = l
    var continue = true
    while (!these.isEmpty && continue) {
      b += these.head
      continue = p(these.head)
      these = these.tail
    }
    (b.toList, these)
  }

  /**
   * The same effect but using List's span
   * Uses boolean; works for including one elem only
   */
  def spanInclusive2(p: A => Boolean): (List[A], List[A]) = {
    var virgin = true
    l span { e =>
      if (!p(e) && virgin == true) {
        virgin = false
        true
      } else {
        virgin
      }
    }
  }

  /**
   * Uses integer variable. Includes one more.
   */
  def spanPlus1(p: A => Boolean): (List[A], List[A]) = {
    var found = 0
    l span { e =>
      if (!p(e) || found > 0) found += 1
      found <= 1
    }
  }

  /**
   * Uses integer variable. Includes two more.
   */
  def spanPlus2(p: A => Boolean): (List[A], List[A]) = {
    var found = 0
    l span { e =>
      if (!p(e) || found > 0) found += 1
      found <= 2
    }
  }

  /**
   * Uses integer variable. Can include n more.
   */
  def spanPlusN(n: Int)(p: A => Boolean): (List[A], List[A]) = {
    var found = 0
    l span { e =>
      if (!p(e) || found > 0) found += 1
      found <= n
    }
  }
}

object ListSpanVariations {
  implicit def listToListSpanVariations[A](l: List[A]): ListSpanVariations[A] = {
    new ListSpanVariations(l)
  }
}