completed rationals + added IntSet base

src/Assignment3/IntSet.sc

@@ -0,0 +1,27 @@
+abstract class IntSet() {
+  def add(x: Int): IntSet
+  def contains(x: Int): Boolean
+}
+
+class NonEmpty(elem: Int, left: IntSet, right: IntSet) extends IntSet() {
+  def add(x: Int): IntSet = {
+    if (x < elem) new NonEmpty(elem, left add x, right)
+    else if (x > elem) new NonEmpty(elem, left, right add x)
+    else this
+  }
+
+  def contains(x: Int): Boolean =
+    if (x < elem) left contains x
+    else if (x > elem) right contains x
+    else true
+}
+
+class Empty extends IntSet() {
+  def add(x: Int): IntSet = new NonEmpty(x, new Empty(), new Empty)
+  def contains(x: Int): Boolean = false
+}
+
+val t1 = new Empty()
+val t2 = t1 add 3
+val t3 = t1 add 4 add 5 add 2 add 6
+t3 contains 4