--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/parser3.scala	Mon Nov 19 14:18:42 2012 +0000
@@ -0,0 +1,32 @@
+
+// parser combinators with input type I and return type T
+
+abstract class Parser[I <% Seq[_], 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)
+  def ~>[S] (right : => Parser[I, S]) : Parser[I, S] = this ~ right ==> (_._2)
+  def <~[S] (right : => Parser[I, S]) : Parser[I, T] = this ~ right ==> (_._1)
+}
+
+class SeqParser[I <% Seq[_], T, S](p: => Parser[I, T], q: => Parser[I, S]) extends Parser[I, (T, S)] {
+  def parse(sb: I) = 
+    for ((head1, tail1) <- p.parse(sb); 
+         (head2, tail2) <- q.parse(tail1)) yield ((head1, head2), tail2)
+}
+
+class AltParser[I <% Seq[_], T](p: => Parser[I, T], q: => Parser[I, T]) extends Parser[I, T] {
+  def parse(sb: I) = p.parse(sb) ++ q.parse(sb)   
+}
+
+class FunParser[I <% Seq[_], T, S](p: => Parser[I, T], f: T => S) extends Parser[I, S] {
+  def parse(sb: I) = 
+    for ((head, tail) <- p.parse(sb)) yield (f(head), tail)
+}
+
+