added assignment 3 ex 1.2-1.4

src/Assignment3/IntSet.sc

@@ -1,6 +1,7 @@
 abstract class IntSet() {
   def add(x: Int): IntSet
   def contains(x: Int): Boolean
+  def foreach(f: Int => Unit): Unit
 }
 
 class NonEmpty(elem: Int, left: IntSet, right: IntSet) extends IntSet() {
@@ -16,12 +17,20 @@ class NonEmpty(elem: Int, left: IntSet, right: IntSet) extends IntSet() {
     else true
 
   override def toString = "(" + left + "|" + elem + "|" + right + ")"
+
+  def foreach(f: Int => Unit): Unit = {
+    left.foreach(f)
+    f(elem)
+    right.foreach(f)
+  }
 }
 
 object Empty extends IntSet() {
   def add(x: Int): IntSet = new NonEmpty(x, Empty, Empty)
   def contains(x: Int): Boolean = false
   override def toString = "-"
+
+  def foreach(f: Int => Unit): Unit = {}
 }
 
 val t1 = Empty
@@ -32,3 +41,11 @@ t3 contains 4
 println(Empty)                  // prints -
 println(Empty.add(3))           // prints (-|3|-)
 println(Empty.add(3).add(2))    // prints ((-|2|-)|3|-)
+
+val s = Empty.add(3).add(2).add(7).add(1)
+s.foreach(println)
+
+(Empty.add(3).add(2).add(6).add(1)) foreach (x => print(x+1 + ", "))
+// 2, 3, 4, 7,
+// Because a BST is always sorted
+