diff -r e7d0157f0471 -r 16742bf62365 progs/app05.scala
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/progs/app05.scala	Sat Oct 08 16:44:11 2016 +0100
@@ -0,0 +1,21 @@
+def simp(r: Rexp): (Rexp, Val => Val) = r match {
+  case ALT(r1, r2) => {
+    val (r1s, f1s) = simp(r1)
+    val (r2s, f2s) = simp(r2)
+    (r1s, r2s) match {
+      case (NULL, _) => (r2s, F_RIGHT(f2s))
+      case (_, NULL) => (r1s, F_LEFT(f1s))
+      case _ => 
+         if (r1s == r2s) (r1s, F_LEFT(f1s))
+         else (ALT (r1s, r2s), F_ALT(f1s, f2s)) 
+    }
+  }
+  ...
+}
+
+def F_RIGHT(f: Val => Val) = (v:Val) => Right(f(v))
+def F_LEFT(f: Val => Val) = (v:Val) => Left(f(v))
+def F_ALT(f1: Val => Val, f2: Val => Val) = 
+  (v:Val) => v match {
+    case Right(v) => Right(f2(v))
+    case Left(v) => Left(f1(v)) }