added assignment 4 ex 1

src/Assignment4/Ex1_Expressions.sc

@@ -0,0 +1,60 @@
+sealed abstract class Expr
+case class Number(n: Int) extends Expr
+case class Sum(e1: Expr, e2: Expr) extends Expr
+case class Product(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)
+  case Product(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)
+  case Product(e1, e2) => {
+    val left: String = e1 match {
+      case Sum(e1a, e1b) => "(" + show(e1) + ")"
+      case _ => show(e1)
+    }
+    val right: String = e2 match {
+      case Sum(e2a, e2b) => "(" + show(e2) + ")"
+      case _ => show(e2)
+    }
+    left + " * " + right
+  }
+}
+
+val e1: Expr = Sum(Number(1), Sum(Number(2), Number(3)))
+eval(e1)
+show(e1)
+
+val e2: Expr = Sum(
+  Number(2),
+  Product(
+    Number(3),
+    Sum(
+      Number(4),
+      Number(5)
+    )
+  )
+)
+eval(e2)
+show(e2)
+
+
+val expr0 = Sum(Product(Number(2), Number(3)), Number(4))
+println("Expr0: " + show(expr0))  // Expr0: 2*3+4
+assert(eval(expr0) == 10)
+
+val expr1 = Product(Number(4), Number(12))
+println("Expr1: " + show(expr1))  // Expr1: 4*12
+assert(eval(expr1) == 48)
+
+val expr2 = Product(Sum(Number(2), Number(3)), Number(4))
+println("Expr2: " + show(expr2))  // Expr2: (2+3)*4
+assert(eval(expr2) == 20)
+
+val expr3 = Product(Number(2), Sum(Number(3), Number(4)))
+println("Expr3: " + show(expr3))  // Expr3: 2*(3+4)
+assert(eval(expr3) == 14)