Add Option.{when,unless}

src/library/scala/Option.scala

@@ -28,6 +28,19 @@ object Option {
    *  the collections hierarchy.
    */
   def empty[A] : Option[A] = None
+
+  /** When a given condition is true, evaluates the `a` argument and returns
+   *  Some(a). When the condition is false, `a` is not evaluated and None is
+   *  returned.
+   */
+  def when[A](cond: Boolean)(a: => A): Option[A] =
+    if (cond) Some(a) else None
+
+  /** Unless a given condition is true, this will evaluate the `a` argument and
+   *  return Some(a). Otherwise, `a` is not evaluated and None is returned.
+   */
+  @inline def unless[A](cond: Boolean)(a: => A): Option[A] =
+    when(!cond)(a)
 }
 
 /** Represents optional values. Instances of `Option`