A-M baby

Task/History-variables/Scala/history-variables-1.scala

@@ -0,0 +1,20 @@
+class HVar[A](initialValue: A) extends Proxy {
+  override def self = !this
+  override def toString = "HVar(" + !this + ")"
+
+  def history = _history
+
+  private var _history = List(initialValue)
+  def unary_! = _history.head
+  def :=(newValue: A): Unit = {
+    _history = newValue :: _history
+  }
+  def modify(f: A => A): Unit = {
+    _history = f(!this) :: _history
+  }
+  def undo: A = {
+    val v = !this
+    _history = _history.tail
+    v
+  }
+}

Task/History-variables/Scala/history-variables-2.scala

@@ -0,0 +1,21 @@
+scala> val h = new HVar(3)
+h: HVar[Int] = HVar(3)
+
+scala> h := 11
+
+scala> h := 90
+
+scala> !h
+res32: Int = 90
+
+scala> h.history
+res33: List[Int] = List(90, 11, 3)
+
+scala> h.undo
+res34: Int = 90
+
+scala> h.undo
+res35: Int = 11
+
+scala> h.undo
+res36: Int = 3