added lesson 4

src/Lesson4/Lists.sc

@@ -0,0 +1,13 @@
+def insert(x: Int, xs: List[Int]): List[Int] = {
+  if (xs.isEmpty) x::Nil
+  else if (x < xs.head) x::xs
+  else xs.head::insert(x, xs.tail)
+}
+
+def isort(xs: List[Int]): List[Int] = {
+  if (xs.isEmpty) Nil
+  else insert(xs.head, isort(xs.tail))
+}
+
+
+isort(7::3::9::2::Nil)

src/Lesson4/PatternMatching.sc

@@ -0,0 +1,35 @@
+def patFoo(value: Any): Boolean = {
+  value match {
+    case a: Int => a % 4 == 0
+    case c: Char => c.isUpper
+    case b: Boolean => true
+    case _ => false
+  }
+}
+
+abstract class Expr
+case class Number(n: Int) extends Expr
+case class Sum(e1: Expr, e2: Expr) extends Expr
+
+def eval(e: Expr): Int = e match {
+  case Number(n) => n
+  case Sum(e1, e2) => eval(e1) + eval(e2)
+}
+
+def show(e: Expr): String = e match {
+  case Number(n) => n.toString
+  case Sum(e1, e2) => "(" + show(e1) + " + " + show(e2) + ")"
+}
+
+patFoo(23)
+patFoo(24)
+patFoo('a')
+patFoo('A')
+patFoo(false)
+patFoo(true)
+patFoo("Hello")
+patFoo(null)
+
+val e: Expr = Sum(Number(3), Sum(Number(4), Number(5)))
+eval(e)
+show(e)

src/Lesson4/Types.sc

@@ -0,0 +1,4 @@
+val a: String = "Hell" + "o" * 50
+def b(s: String): String = "Hell" + s
+
+a == b("o" * 50)