diff -r 47f86885d481 -r e85600529ca5 regexp.scala
--- a/regexp.scala	Sun Dec 23 00:38:56 2012 +0000
+++ /dev/null	Thu Jan 01 00:00:00 1970 +0000
@@ -1,106 +0,0 @@
-// regular expressions
-abstract class Rexp
-
-case object NULL extends Rexp
-case object EMPTY 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
-def charlist2rexp(s : List[Char]) : Rexp = s match {
-  case Nil => EMPTY
-  case c::Nil => CHAR(c)
-  case c::s => SEQ(CHAR(c), charlist2rexp(s))
-}
-implicit def string2rexp(s : String) : Rexp = charlist2rexp(s.toList)
-
-
-// for example
-println(STAR("abc"))
-
-// produces STAR(SEQ(CHAR(a),SEQ(CHAR(b),SEQ(CHAR(c),EMPTY))))
-
-
-
-// a simple-minded regular expression matcher:
-// it loops for examples like STAR(EMPTY) with
-// strings this regular expression does not match
-
-def smatchers(rs: List[Rexp], s: List[Char]) : Boolean = (rs, s) match {
-  case (NULL::rs, s) => false
-  case (EMPTY::rs, s) => smatchers(rs, s)
-  case (CHAR(c)::rs, Nil) => false
-  case (CHAR(c)::rs, d::s) => (c ==d) && smatchers(rs, s) 
-  case (ALT(r1, r2)::rs, s) => smatchers(r1::rs, s) || smatchers(r2::rs, s)
-  case (SEQ(r1, r2)::rs, s) => smatchers(r1::r2::rs, s) 
-  case (STAR(r)::rs, s) => smatchers(rs, s) || smatchers(r::STAR(r)::rs, s) 
-  case (Nil, s) => s == Nil
-}
-
-def smatcher(r: Rexp, s: String) = smatchers(List(r), s.toList)
-
-// regular expression: a
-println(smatcher(CHAR('a'), "ab")) 
-
-// regular expression: a + (b o c)
-println(smatcher(ALT(CHAR('a'), SEQ(CHAR('b'), CHAR('c'))), "ab")) 
-
-// regular expression: a + (b o c)
-println(smatcher(ALT(CHAR('a'), SEQ(CHAR('b'), CHAR('c'))), "bc")) 
-
-// loops for regular expression epsilon* 
-//println(smatcher(STAR(EMPTY), "a"))
-
-
-
-// Regular expression matcher that works properly
-//================================================
-
-// nullable function: tests whether the regular 
-// expression can recognise the empty string
-def nullable (r: Rexp) : Boolean = r match {
-  case NULL => false
-  case EMPTY => true
-  case CHAR(_) => false
-  case ALT(r1, r2) => nullable(r1) || nullable(r2)
-  case SEQ(r1, r2) => nullable(r1) && nullable(r2)
-  case STAR(_) => true
-}
-
-// derivative of a regular expression w.r.t. a character
-def der (c: Char, r: Rexp) : Rexp = r match {
-  case NULL => NULL
-  case EMPTY => NULL
-  case CHAR(d) => if (c == d) EMPTY else NULL
-  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))
-}
-
-// derivative w.r.t. a string (iterates der)
-def ders (s: List[Char], r: Rexp) : Rexp = s match {
-  case Nil => r
-  case c::s => ders(s, der(c, r))
-}
-
-// main matcher function
-def matcher(r: Rexp, s: String) : Boolean = nullable(ders(s.toList, r))
-
-
-//examples
-
-println(matcher(SEQ(STAR("a"), STAR("b")), "bbaaa"))
-println(matcher(ALT(STAR("a"), STAR("b")), ""))
-println(matcher("abc", ""))
-println(matcher(STAR(ALT(EMPTY, "a")), ""))
-println(matcher(STAR(EMPTY), "a"))
-println(matcher("cab","cab"))
-println(matcher(STAR("a"),"aaa"))
-println(matcher("cab" ,"cab"))
-println(matcher(STAR("a"),"aaa"))
-
-