Add clear method to Lst.Buffer

Plus some polishings

Author: odersky

tests/run/lst/Lst.scala

@@ -5,12 +5,14 @@ import printing.{Printer, Texts}
 import Texts.Text
 import collection.mutable.{ListBuffer, StringBuilder}
 
-//      List    Lst
-// 0    0       0
-// 1    1       0
-// 2    2       1
-// 3    3       1
-// 4    4       1
+
+/** A lightweight class for lists, optimized for short and medium lengths.
+ *  A list is represented at runtime as
+ *
+ *    If it is empty:               the value `Lst.Empty`
+ *    If it contains one element:   the element itself
+ *    If it contains more elements: an Array[AnyRef] containing the elements
+ */
 class Lst[+T <: AnyRef](val elems: AnyRef) extends AnyVal {
   import Lst._
 
@@ -418,8 +420,7 @@ object Lst {
     new Lst(elems)
   }
 
-  val eqFn = (x: AnyRef, y: AnyRef) => x `eq` y
-  val equalsFn = (x: AnyRef, y: AnyRef) => x `equals` y
+  private val eqFn = (x: AnyRef, y: AnyRef) => x `eq` y
 
   class Buffer[T <: AnyRef] {
     private var len = 0
@@ -469,6 +470,9 @@ object Lst {
       if (len == 0) Empty
       else if (len == 1) new Lst(elem)
       else _fromArray(elems, 0, len)
+
+    def clear() =
+      len = 0
   }
 
   private def _fromArray[T <: AnyRef](elems: Arr, start: Int, end: Int): Lst[T] = {