--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/progs/re2.scala	Wed Nov 30 10:07:05 2016 +0000
@@ -0,0 +1,68 @@
+// Part 2 about Regular Expression Matching
+//==========================================
+
+// copy over all code from re.scala
+
+// (2a) Complete the function iterT which needs to
+// be tail-recursive(!) and takes an integer n, a 
+// function f and an x as arguments. This function 
+// should iterate f n-times starting with the 
+// argument x.
+
+import scala.annotation.tailrec
+
+@tailrec
+def iterT[A](n: Int, f: A => A, x: A): A = ...
+
+
+
+// (2b) Complete the size function for regular
+// expressions 
+
+def size(r: Rexp): Int = ...
+
+// two testcases about the sizes of simplified and 
+// un-simplified derivatives
+
+//val EVIL = SEQ(STAR(STAR(CHAR('a'))), CHAR('b'))
+//size(iterT(20, (r: Rexp) => der('a', r), EVIL))        // should produce 7340068
+//size(iterT(20, (r: Rexp) => simp(der('a', r)), EVIL))  // should produce 8
+
+
+
+// (2c) Complete the fixpoint function below.
+
+@tailrec
+def fixpT[A](f: A => A, x: A): A = ...
+
+
+/* testcases
+
+//the Collatz function from CW 6 defined as fixpoint
+
+def ctest(n: Long): Long =
+  if (n == 1) 1 else
+    if (n % 2 == 0) n / 2 else 3 * n + 1
+
+// should all produce 1 
+fixpT(ctest, 97L)
+fixpT(ctest, 871L)
+fixpT(ctest, 77031L)
+
+*/
+
+/*
+// the same function on strings using the regular expression
+// matcher
+   
+def foo(s: String): String = {
+  if (matcher("a", s)) "a" else
+  if (matcher("aa" ~ STAR("aa"), s)) s.take(s.length / 2) 
+  else "a" ++ s * 3
+}
+
+// should all produce "a" 
+fixpT(foo, "a" * 97)
+fixpT(foo, "a" * 871)
+
+*/