diff -r 663c2a9108d1 -r 4de31fdc0d67 testing4/re.scala
--- a/testing4/re.scala Sun Nov 01 01:21:31 2020 +0000
+++ /dev/null Thu Jan 01 00:00:00 1970 +0000
@@ -1,196 +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 // alternative
-case class SEQ(r1: Rexp, r2: Rexp) extends Rexp // sequence
-case class STAR(r: Rexp) extends Rexp // star
-
-
-// some convenience for typing 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)
-}
-
-// (5) 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(c) => false
- case ALT(r1, r2) => (nullable(r1) || nullable(r2))
- case SEQ(r1, r2) => (nullable(r1) && nullable(r2))
- case STAR(r) => true
- }
-}
-
-// (6) 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(d == c) 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(r) => SEQ(der(c, r), STAR(r))
- }
-}
-
-
-// (7) 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 STAR(r) => STAR(r) // does not process r star
- case SEQ(r1, r2) => {
- val x = (simp(r1), simp(r2))
- if(x._1 == ZERO) ZERO else
- if(x._2 == ZERO) ZERO else
- if(x._1 == ONE) simp(x._2) else
- if(x._2 == ONE) simp(x._1) else
- if(x._1 == x._2) simp(x._2) else
- SEQ(simp(x._1), simp(x._2))
- }
- case ALT(r1, r2) => {
- val x = (simp(r1), simp(r2))
- if(x._1 == ZERO) simp(x._2) else
- if(x._2 == ZERO) simp(x._1) else
- if(x._1 == x._2) simp(x._2) else
- ALT(simp(x._1), simp(x._2))
- }
- case r => r // if single regex, return it
- }
-}
-
-
-// (8) 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 :: cs => ders(cs, simp(der(c,r)))
- }
-}
-
-def matcher(r: Rexp, s: String): Boolean = {
- val listOfCharacters = s.toList
- val result = ders(listOfCharacters, r)
- nullable(result)
-}
-
-
-// (9) 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(c) => 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)
- }
-}
-
-// 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
-// 30 seconds.
-//
-// Lets see how long it really 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))))
-}
-
-// another "power" test case
-simp(Iterator.iterate(ONE:Rexp)(r => SEQ(r, ONE | ONE)).drop(50).next) == ONE
-
-// the Iterator produces the rexp
-//
-// SEQ(SEQ(SEQ(..., ONE | ONE) , ONE | ONE), ONE | ONE)
-//
-// where SEQ is nested 50 times.
-
-*/
-
-}