diff -r e66bd5c563eb -r b5b5583a3a08 progs/re2.scala
--- a/progs/re2.scala	Mon Jul 27 11:02:48 2020 +0100
+++ /dev/null	Thu Jan 01 00:00:00 1970 +0000
@@ -1,118 +0,0 @@
-// A Version with an explicit n-times regular expression;
-// this keeps the size of the regular expression in the
-// EVIL1 test-case quite small
-
-abstract class Rexp 
-case object ZERO extends Rexp
-case object ONE extends Rexp
-case class CHAR(c: Char) extends Rexp
-case class ALT(r1: Rexp, r2: Rexp) extends Rexp 
-case class SEQ(r1: Rexp, r2: Rexp) extends Rexp 
-case class STAR(r: Rexp) extends Rexp 
-case class NTIMES(r: Rexp, n: Int) extends Rexp   //explicit constructor for n-times
-
-
-def nullable (r: Rexp) : Boolean = r match {
-  case ZERO => false
-  case ONE => true
-  case CHAR(_) => false
-  case ALT(r1, r2) => nullable(r1) || nullable(r2)
-  case SEQ(r1, r2) => nullable(r1) && nullable(r2)
-  case STAR(_) => true
-  case NTIMES(r, i) => if (i == 0) true else nullable(r)
-}
-
-
-def der (c: Char, r: Rexp) : Rexp = r match {
-  case ZERO => ZERO
-  case ONE => ZERO
-  case CHAR(d) => if (c == d) ONE else ZERO
-  case ALT(r1, r2) => ALT(der(c, r1), der(c, r2))
-  case SEQ(r1, r2) => 
-    if (nullable(r1)) ALT(SEQ(der(c, r1), r2), der(c, r2))
-    else SEQ(der(c, r1), r2)
-  case STAR(r1) => SEQ(der(c, r1), STAR(r1))
-  case NTIMES(r1, i) => 
-    if (i == 0) ZERO else SEQ(der(c, r1), NTIMES(r1, i - 1))
-}
-
-def ders (s: List[Char], r: Rexp) : Rexp = s match {
-  case Nil => r
-  case c::s => ders(s, der(c, r))
-}
-
-def matcher(r: Rexp, s: String) : Boolean = nullable(ders(s.toList, r))
-
-
-// the optional regular expression: one or zero times
-// this regular expression is still defined in terms of ALT
-def OPT(r: Rexp) = ALT(r, ONE)
-
-
-// Test Cases
-
-// evil regular expressions
-def EVIL1(n: Int) = SEQ(NTIMES(OPT(CHAR('a')), n), NTIMES(CHAR('a'), n))
-val EVIL2 = SEQ(STAR(STAR(CHAR('a'))), CHAR('b'))
-
-def time_needed[T](i: Int, code: => T) = {
-  val start = System.nanoTime()
-  for (j <- 1 to i) code
-  val end = System.nanoTime()
-  (end - start) / (i * 1.0e9)
-}
-
-
-
-// test: (a?{n}) (a{n})
-for (i <- 0 to 1000 by 100) {
-  println(f"$i: ${time_needed(2, matcher(EVIL1(i), "a" * i))}%.5f")
-}
-
-// test: (a*)* b
-for (i <- 0 to 20) {
-  println(f"$i: ${time_needed(2, matcher(EVIL2, "a" * i))}%.5f")
-}
-
-
-// the size of a regular expressions - for testing purposes 
-def size(r: Rexp) : Int = r match {
-  case ZERO => 1
-  case ONE => 1
-  case CHAR(_) => 1
-  case ALT(r1, r2) => 1 + size(r1) + size(r2)
-  case SEQ(r1, r2) => 1 + size(r1) + size(r2)
-  case STAR(r) => 1 + size(r)
-  case NTIMES(r, _) => 1 + size(r)
-}
-
-// EVIL1(n) has now a constant size, no matter
-// what n is; also the derivative only grows 
-// moderately 
-
-size(EVIL1(1))  // 7
-size(EVIL1(3))  // 7
-size(EVIL1(5))  // 7
-size(EVIL1(7))  // 7
-size(EVIL1(20)) // 7
-
-size(ders("".toList, EVIL1(5)))       // 7
-size(ders("a".toList, EVIL1(5)))      // 16
-size(ders("aa".toList, EVIL1(5)))     // 35
-size(ders("aaa".toList, EVIL1(5)))    // 59
-size(ders("aaaa".toList, EVIL1(5)))   // 88
-size(ders("aaaaa".toList, EVIL1(5)))  // 122
-size(ders("aaaaaa".toList, EVIL1(5))) // 151
-
-// but the size of the derivatives can still grow 
-// quite dramatically in case of EVIL2
-
-size(ders("".toList, EVIL2))       // 5
-size(ders("a".toList, EVIL2))      // 12
-size(ders("aa".toList, EVIL2))     // 28
-size(ders("aaa".toList, EVIL2))    // 58
-size(ders("aaaa".toList, EVIL2))   // 116
-size(ders("aaaaa".toList, EVIL2))  // 230
-size(ders("aaaaaa".toList, EVIL2)) // 456
-
-size(ders(("a" * 20).toList, EVIL2)) // 7340068
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