1 // A simple tokeniser based on the Sulzmann & Lu algorithm

     2 //=========================================================

     3 // 

     4 // call with 

     5 //

     6 //     scala tokenise.scala fib.while

     7 //

     8 //     scala tokenise.scala loops.while

     9 //

    10 // this will generate a .tks file that can be deserialised back

    11 // into a list of tokens

    12 // you can add -Xno-patmat-analysis in order to get rid of the

    13 // match-not-exhaustive warning

    14 

    15 object Tokenise {

    16 

    17 import scala.language.implicitConversions    

    18 import scala.language.reflectiveCalls

    19 

    20 // regular expressions including records

    21 abstract class Rexp 

    22 case object ZERO extends Rexp

    23 case object ONE extends Rexp

    24 case class CHAR(c: Char) extends Rexp

    25 case class ALT(r1: Rexp, r2: Rexp) extends Rexp 

    26 case class SEQ(r1: Rexp, r2: Rexp) extends Rexp 

    27 case class STAR(r: Rexp) extends Rexp 

    28 case class RECD(x: String, r: Rexp) extends Rexp

    29   

    30 // values  

    31 abstract class Val

    32 case object Empty extends Val

    33 case class Chr(c: Char) extends Val

    34 case class Sequ(v1: Val, v2: Val) extends Val

    35 case class Left(v: Val) extends Val

    36 case class Right(v: Val) extends Val

    37 case class Stars(vs: List[Val]) extends Val

    38 case class Rec(x: String, v: Val) extends Val

    39    

    40 // some convenience for typing in regular expressions

    41 def charlist2rexp(s : List[Char]): Rexp = s match {

    42   case Nil => ONE

    43   case c::Nil => CHAR(c)

    44   case c::s => SEQ(CHAR(c), charlist2rexp(s))

    45 }

    46 implicit def string2rexp(s : String) : Rexp = 

    47   charlist2rexp(s.toList)

    48 

    49 implicit def RexpOps(r: Rexp) = new {

    50   def | (s: Rexp) = ALT(r, s)

    51   def % = STAR(r)

    52   def ~ (s: Rexp) = SEQ(r, s)

    53 }

    54 

    55 implicit def stringOps(s: String) = new {

    56   def | (r: Rexp) = ALT(s, r)

    57   def | (r: String) = ALT(s, r)

    58   def % = STAR(s)

    59   def ~ (r: Rexp) = SEQ(s, r)

    60   def ~ (r: String) = SEQ(s, r)

    61   def $ (r: Rexp) = RECD(s, r)

    62 }

    63 

    64 def nullable(r: Rexp) : Boolean = r match {

    65   case ZERO => false

    66   case ONE => true

    67   case CHAR(_) => false

    68   case ALT(r1, r2) => nullable(r1) || nullable(r2)

    69   case SEQ(r1, r2) => nullable(r1) && nullable(r2)

    70   case STAR(_) => true

    71   case RECD(_, r1) => nullable(r1)

    72 }

    73 

    74 def der(c: Char, r: Rexp) : Rexp = r match {

    75   case ZERO => ZERO

    76   case ONE => ZERO

    77   case CHAR(d) => if (c == d) ONE else ZERO

    78   case ALT(r1, r2) => ALT(der(c, r1), der(c, r2))

    79   case SEQ(r1, r2) => 

    80     if (nullable(r1)) ALT(SEQ(der(c, r1), r2), der(c, r2))

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

    82   case STAR(r) => SEQ(der(c, r), STAR(r))

    83   case RECD(_, r1) => der(c, r1)

    84 }

    85 

    86 

    87 // extracts a string from value

    88 def flatten(v: Val) : String = v match {

    89   case Empty => ""

    90   case Chr(c) => c.toString

    91   case Left(v) => flatten(v)

    92   case Right(v) => flatten(v)

    93   case Sequ(v1, v2) => flatten(v1) + flatten(v2)

    94   case Stars(vs) => vs.map(flatten).mkString

    95   case Rec(_, v) => flatten(v)

    96 }

    97 

    98 

    99 // extracts an environment from a value;

   100 // used for tokenise a string

   101 def env(v: Val) : List[(String, String)] = v match {

   102   case Empty => Nil

   103   case Chr(c) => Nil

   104   case Left(v) => env(v)

   105   case Right(v) => env(v)

   106   case Sequ(v1, v2) => env(v1) ::: env(v2)

   107   case Stars(vs) => vs.flatMap(env)

   108   case Rec(x, v) => (x, flatten(v))::env(v)

   109 }

   110 

   111 // The Injection Part of the lexer

   112 

   113 def mkeps(r: Rexp) : Val = r match {

   114   case ONE => Empty

   115   case ALT(r1, r2) => 

   116     if (nullable(r1)) Left(mkeps(r1)) else Right(mkeps(r2))

   117   case SEQ(r1, r2) => Sequ(mkeps(r1), mkeps(r2))

   118   case STAR(r) => Stars(Nil)

   119   case RECD(x, r) => Rec(x, mkeps(r))

   120 }

   121 

   122 def inj(r: Rexp, c: Char, v: Val) : Val = (r, v) match {

   123   case (STAR(r), Sequ(v1, Stars(vs))) => Stars(inj(r, c, v1)::vs)

   124   case (SEQ(r1, r2), Sequ(v1, v2)) => Sequ(inj(r1, c, v1), v2)

   125   case (SEQ(r1, r2), Left(Sequ(v1, v2))) => Sequ(inj(r1, c, v1), v2)

   126   case (SEQ(r1, r2), Right(v2)) => Sequ(mkeps(r1), inj(r2, c, v2))

   127   case (ALT(r1, r2), Left(v1)) => Left(inj(r1, c, v1))

   128   case (ALT(r1, r2), Right(v2)) => Right(inj(r2, c, v2))

   129   case (CHAR(d), Empty) => Chr(c) 

   130   case (RECD(x, r1), _) => Rec(x, inj(r1, c, v))

   131 }

   132 

   133 // some "rectification" functions for simplification

   134 def F_ID(v: Val): Val = v

   135 def F_RIGHT(f: Val => Val) = (v:Val) => Right(f(v))

   136 def F_LEFT(f: Val => Val) = (v:Val) => Left(f(v))

   137 def F_ALT(f1: Val => Val, f2: Val => Val) = (v:Val) => v match {

   138   case Right(v) => Right(f2(v))

   139   case Left(v) => Left(f1(v))

   140 }

   141 def F_SEQ(f1: Val => Val, f2: Val => Val) = (v:Val) => v match {

   142   case Sequ(v1, v2) => Sequ(f1(v1), f2(v2))

   143 }

   144 def F_SEQ_Empty1(f1: Val => Val, f2: Val => Val) = 

   145   (v:Val) => Sequ(f1(Empty), f2(v))

   146 def F_SEQ_Empty2(f1: Val => Val, f2: Val => Val) = 

   147   (v:Val) => Sequ(f1(v), f2(Empty))

   148 def F_RECD(f: Val => Val) = (v:Val) => v match {

   149   case Rec(x, v) => Rec(x, f(v))

   150 }

   151 def F_ERROR(v: Val): Val = throw new Exception("error")

   152 

   153 def simp(r: Rexp): (Rexp, Val => Val) = r match {

   154   case ALT(r1, r2) => {

   155     val (r1s, f1s) = simp(r1)

   156     val (r2s, f2s) = simp(r2)

   157     (r1s, r2s) match {

   158       case (ZERO, _) => (r2s, F_RIGHT(f2s))

   159       case (_, ZERO) => (r1s, F_LEFT(f1s))

   160       case _ => if (r1s == r2s) (r1s, F_LEFT(f1s))

   161                 else (ALT (r1s, r2s), F_ALT(f1s, f2s)) 

   162     }

   163   }

   164   case SEQ(r1, r2) => {

   165     val (r1s, f1s) = simp(r1)

   166     val (r2s, f2s) = simp(r2)

   167     (r1s, r2s) match {

   168       case (ZERO, _) => (ZERO, F_ERROR)

   169       case (_, ZERO) => (ZERO, F_ERROR)

   170       case (ONE, _) => (r2s, F_SEQ_Empty1(f1s, f2s))

   171       case (_, ONE) => (r1s, F_SEQ_Empty2(f1s, f2s))

   172       case _ => (SEQ(r1s,r2s), F_SEQ(f1s, f2s))

   173     }

   174   }

   175   case r => (r, F_ID)

   176 }

   177 

   178 // lexing functions including simplification

   179 def lex_simp(r: Rexp, s: List[Char]) : Val = s match {

   180   case Nil => if (nullable(r)) mkeps(r) else 

   181     { throw new Exception("lexing error") } 

   182   case c::cs => {

   183     val (r_simp, f_simp) = simp(der(c, r))

   184     inj(r, c, f_simp(lex_simp(r_simp, cs)))

   185   }

   186 }

   187 

   188 def lexing_simp(r: Rexp, s: String) = 

   189   env(lex_simp(r, s.toList))

   190 

   191 

   192 // The Lexing Rules for the WHILE Language

   193 

   194 // inefficient representations for some extended regular

   195 // expressions

   196 def PLUS(r: Rexp) = r ~ r.%

   197 

   198 def Range(s : List[Char]) : Rexp = s match {

   199   case Nil => ZERO

   200   case c::Nil => CHAR(c)

   201   case c::s => ALT(CHAR(c), Range(s))

   202 }

   203 def RANGE(s: String) = Range(s.toList)

   204 

   205 val SYM = RANGE("ABCDEFGHIJKLMNOPQRSTUVXYZabcdefghijklmnopqrstuvwxyz_")

   206 val DIGIT = RANGE("0123456789")

   207 val ID = SYM ~ (SYM | DIGIT).% 

   208 val NUM = PLUS(DIGIT)

   209 val KEYWORD : Rexp = "skip" | "while" | "do" | "if" | "then" | "else" | "read" | "write" 

   210 val SEMI: Rexp = ";"

   211 val OP: Rexp = ":=" | "=" | "-" | "+" | "*" | "!=" | "<" | ">"

   212 val WHITESPACE = PLUS(" " | "\n" | "\t")

   213 val RPAREN: Rexp = "{"

   214 val LPAREN: Rexp = "}"

   215 val STRING: Rexp = "\"" ~ SYM.% ~ "\""

   216 

   217 

   218 val WHILE_REGS = (("k" $ KEYWORD) | 

   219                   ("i" $ ID) | 

   220                   ("o" $ OP) | 

   221                   ("n" $ NUM) | 

   222                   ("s" $ SEMI) | 

   223                   ("str" $ STRING) |

   224                   ("p" $ (LPAREN | RPAREN)) | 

   225                   ("w" $ WHITESPACE)).%

   226 

   227 

   228 

   229 // Generate tokens for the WHILE language

   230 // and serialise them into a .tks file

   231 

   232 import java.io._

   233 

   234 abstract class Token extends Serializable 

   235 case object T_SEMI extends Token

   236 case object T_LPAREN extends Token

   237 case object T_RPAREN extends Token

   238 case class T_ID(s: String) extends Token

   239 case class T_OP(s: String) extends Token

   240 case class T_NUM(n: Int) extends Token

   241 case class T_KWD(s: String) extends Token

   242 case class T_STR(s: String) extends Token

   243 

   244 // transforms pairs into tokens

   245 val token : PartialFunction[(String, String), Token] = {

   246   case ("s", _) => T_SEMI

   247   case ("p", "{") => T_LPAREN

   248   case ("p", "}") => T_RPAREN

   249   case ("i", s) => T_ID(s)

   250   case ("o", s) => T_OP(s)

   251   case ("n", s) => T_NUM(s.toInt)

   252   case ("k", s) => T_KWD(s)

   253   case ("str", s) => T_STR(s)

   254 }

   255 

   256 // filters out all un-interesting tokens

   257 def tokenise(s: String) : List[Token] = 

   258   lexing_simp(WHILE_REGS, s).collect(token)

   259 

   260 

   261 def serialise[T](fname: String, data: T) = {

   262   import scala.util.Using

   263   Using(new ObjectOutputStream(new FileOutputStream(fname))) {

   264     out => out.writeObject(data)

   265   }

   266 }

   267 

   268 def main(args: Array[String]) : Unit = {

   269   val fname = args(0)

   270   val tname = fname.stripSuffix(".while") ++ ".tks"

   271   val file = io.Source.fromFile(fname).mkString

   272   serialise(tname, tokenise(file))

   273 }

   274 

   275 

   276 }