--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/progs/app7.scala	Sat Jun 15 09:23:18 2013 -0400
@@ -0,0 +1,16 @@
+abstract class Parser[I, T] {
+  def parse(ts: I): Set[(T, I)]
+
+  def parse_all(ts: I) : Set[T] =
+    for ((head, tail) <- parse(ts); if (tail.isEmpty)) 
+      yield head
+
+  def || (right : => Parser[I, T]) : Parser[I, T] = 
+      new AltParser(this, right)
+  def ==>[S] (f: => T => S) : Parser [I, S] = 
+      new FunParser(this, f)
+   def ~[S] (right : => Parser[I, S]) : Parser[I, (T, S)] = 
+      new SeqParser(this, right)
+}
+
+