33     else SEQ(der(c, r1), r2)

    33     else SEQ(der(c, r1), r2)

    34   case STAR(r1) => SEQ(der(c, r1), STAR(r1))

    34   case STAR(r1) => SEQ(der(c, r1), STAR(r1))

    35   case NTIMES(r1, i) => 

    35   case NTIMES(r1, i) => 

    36     if (i == 0) ZERO else

    36     if (i == 0) ZERO else

    37     if (nullable(r1)) SEQ(der(c, r1), UPNTIMES(r1, i - 1))

    37     if (nullable(r1)) SEQ(der(c, r1), UPNTIMES(r1, i - 1))

    39   case UPNTIMES(r1, i) => 

    39   case UPNTIMES(r1, i) => 

    40     if (i == 0) ZERO

    40     if (i == 0) ZERO

    41     else SEQ(der(c, r1), UPNTIMES(r1, i - 1)) 

    41     else SEQ(der(c, r1), UPNTIMES(r1, i - 1)) 

    42 }

    42 }

    43 

    43 

    65 }

    65 }

    66 

    66 

    67 

    67 

    68 // main matcher function

    68 // main matcher function

    69 def matcher(r: Rexp, s: String) : Boolean = nullable(ders(s.toList, r))

    69 def matcher(r: Rexp, s: String) : Boolean = nullable(ders(s.toList, r))

    71 

    70 

    72 //one or zero

    71 //one or zero

    73 def OPT(r: Rexp) = ALT(r, ONE)

    72 def OPT(r: Rexp) = ALT(r, ONE)

    74 

    73 

    75 //evil regular expressions

    74 //evil regular expressions