1 def matches(r: Rexp, s: String) : Boolean = 

     2   nullable(derivs(r, s.toList))

     3 

     4 

     5 /* Examples */

     6 

     7 println(matches(SEQ(SEQ(CHAR('c'), CHAR('a')), CHAR('b')),"cab"))

     8 println(matches(STAR(CHAR('a')),"aaa"))

     9 

    10 /* Convenience using implicits */

    11 implicit def string2rexp(s : String) : Rexp = {

    12   s.foldRight (EMPTY: Rexp) ( (c, r) => SEQ(CHAR(c), r) )

    13 }

    14 

    15 println(matches("cab" ,"cab"))

    16 println(matches(STAR("a"),"aaa"))

    17 println(matches(STAR("a"),"aaab"))