diff -r 19b75e899d37 -r 9c03b5e89a2a marking4/re.scala
--- a/marking4/re.scala	Fri Apr 26 17:29:30 2024 +0100
+++ /dev/null	Thu Jan 01 00:00:00 1970 +0000
@@ -1,176 +0,0 @@
-// Core Part about Regular Expression Matching
-//=============================================
-
-object CW9c {
-
-// Regular Expressions
-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 
-
-// some convenience for typing in regular expressions
-
-import scala.language.implicitConversions    
-import scala.language.reflectiveCalls 
-
-
-def charlist2rexp(s: List[Char]): Rexp = s match {
-  case Nil => ONE
-  case c::Nil => CHAR(c)
-  case c::s => SEQ(CHAR(c), charlist2rexp(s))
-}
-implicit def string2rexp(s: String): Rexp = charlist2rexp(s.toList)
-
-implicit def RexpOps (r: Rexp) = new {
-  def | (s: Rexp) = ALT(r, s)
-  def % = STAR(r)
-  def ~ (s: Rexp) = SEQ(r, s)
-}
-
-implicit def stringOps (s: String) = new {
-  def | (r: Rexp) = ALT(s, r)
-  def | (r: String) = ALT(s, r)
-  def % = STAR(s)
-  def ~ (r: Rexp) = SEQ(s, r)
-  def ~ (r: String) = SEQ(s, r)
-}
-
-// (1) Complete the function nullable according to
-// the definition given in the coursework; this 
-// function checks whether a regular expression
-// can match the empty string and Returns a boolean
-// accordingly.
-
-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
-}
-
-// (2) Complete the function der according to
-// the definition given in the coursework; this
-// function calculates the derivative of a 
-// regular expression w.r.t. a character.
-
-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))
-}
-
-// (3) Complete the simp function according to
-// the specification given in the coursework; this
-// function simplifies a regular expression from
-// the inside out, like you would simplify arithmetic 
-// expressions; however it does not simplify inside 
-// STAR-regular expressions.
-
-def simp(r: Rexp) : Rexp = r match {
-  case ALT(r1, r2) => (simp(r1), simp(r2)) match {
-    case (ZERO, r2s) => r2s
-    case (r1s, ZERO) => r1s
-    case (r1s, r2s) => if (r1s == r2s) r1s else ALT (r1s, r2s)
-  }
-  case SEQ(r1, r2) =>  (simp(r1), simp(r2)) match {
-    case (ZERO, _) => ZERO
-    case (_, ZERO) => ZERO
-    case (ONE, r2s) => r2s
-    case (r1s, ONE) => r1s
-    case (r1s, r2s) => SEQ(r1s, r2s)
-  }
-  case r => r
-}
-
-
-// (4) Complete the two functions below; the first 
-// calculates the derivative w.r.t. a string; the second
-// is the regular expression matcher taking a regular
-// expression and a string and checks whether the
-// string matches the regular expression.
-
-def ders (s: List[Char], r: Rexp) : Rexp = s match {
-  case Nil => r
-  case c::s => ders(s, simp(der(c, r)))
-}
-
-// main matcher function
-def matcher(r: Rexp, s: String) = nullable(ders(s.toList, r))
-
-// (5) Complete the size function for regular
-// expressions according to the specification 
-// given in the coursework.
-
-
-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(r1) => 1 + size(r1)
-}
-
-
-
-// some testing data
-
-//matcher(("a" ~ "b") ~ "c", "abc")  // => true
-//matcher(("a" ~ "b") ~ "c", "ab")   // => false
-
-// the supposedly 'evil' regular expression (a*)* b
-val EVIL = SEQ(STAR(STAR(CHAR('a'))), CHAR('b'))
-
-//matcher(EVIL, "a" * 1000 ++ "b")   // => true
-//matcher(EVIL, "a" * 1000)          // => false
-
-// size without simplifications
-//size(der('a', der('a', EVIL)))             // => 28
-//size(der('a', der('a', der('a', EVIL))))   // => 58
-
-// size with simplification
-//size(simp(der('a', der('a', EVIL))))           // => 8
-//size(simp(der('a', der('a', der('a', EVIL))))) // => 8
-
-// Python needs around 30 seconds for matching 28 a's with EVIL. 
-// Java 9 and later increase this to an "astonishing" 40000 a's in
-// around 30 seconds.
-//
-// Lets see how long it takes to match strings with 
-// 5 Million a's...it should be in the range of a 
-// couple of seconds.
-
-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)
-}
-
-//for (i <- 0 to 5000000 by 500000) {
-//  println(i + " " + "%.5f".format(time_needed(2, matcher(EVIL, "a" * i))) + " secs.") 
-//}
-
-// another "power" test case 
-//simp(Iterator.iterate(ONE:Rexp)(r => SEQ(r, ONE | ONE)).drop(100).next) == ONE
-
-// the Iterator produces the rexp
-//
-//      SEQ(SEQ(SEQ(..., ONE | ONE) , ONE | ONE), ONE | ONE)
-//
-//    where SEQ is nested 100 times.
- 
-
-
-}