Script started on Mon Mar 29 09:07:07 1999
vestavia% cat PL0.jlex
%%
%{
  private void echo () { 
    System . out . print (yytext ()); 
  }

  public int position () { return yychar; }
%}

%function nextToken
%type      Token
%char
%eofval{
  { return new Token (Token . EOF); }
%eofval}

digit  = [0-9]
letter = [A-Za-z]

%%
[\ \t\n\r] { echo (); }
";"  { echo (); 
       return new Token (Token.SEMICOLON); }
"."  { echo (); 
       return new Token (Token.PERIOD); }
","  { echo (); 
       return new Token (Token.COMMA); }
"<"  { echo (); 
       return new Token (Token.LT); }
"<=" { echo (); 
       return new Token (Token.LE); }
">"  { echo (); 
       return new Token (Token.GT); }
">=" { echo (); 
       return new Token (Token.GE); }
"="  { echo (); 
       return new Token (Token.EQ); }
"<>" { echo (); 
       return new Token (Token.NE); }
"("  { echo (); 
       return new Token (Token.LPAREN); }
")"  { echo (); 
       return new Token (Token.RPAREN); }
"+"  { echo (); 
       return new Token (Token.PLUS); }
"-"  { echo (); 
       return new Token (Token.MINUS); }
"*"  { echo (); 
       return new Token (Token.TIMES); }
"/"  { echo (); 
       return new Token (Token.SLASH); }
":=" { echo (); 
       return new Token (Token.ASSIGN); }
begin { echo (); 
       return new Token (Token.BEGIN); }
call { echo (); 
       return new Token (Token.CALL); }
const { echo (); 
       return new Token (Token.CONST); }
do   { echo (); 
       return new Token (Token.DO); }
end  { echo (); 
       return new Token (Token.END); }
if   { echo (); 
       return new Token (Token.IF); }
odd  { echo (); 
       return new Token (Token.ODD); }
procedure { echo (); 
       return new Token (Token.PROC); }
then { echo (); 
       return new Token (Token.THEN); }
var  { echo (); 
       return new Token (Token.VAR); }
while { echo (); 
       return new Token (Token.WHILE); }
{digit}+ { echo (); 
       return new Token (Token.INTEGER, 
         yytext ()); }
{letter}({letter}|{digit})*  { echo (); 
       return new Token (Token.ID, 
         yytext ()); }
.    { echo (); 
       ErrorMessage.print (yychar, 
         "Illegal character"); }

vestavia% java JLex.Main PL0.jlex
Processing first section -- user code.
Processing second section -- JLex declarations.
Processing third section -- lexical rules.
Creating NFA machine representation.
NFA comprised of 141 states.
Creating DFA transition table.
Working on DFA states.......................................................................
Minimizing DFA transition table.
66 states after removal of redundant states.
Outputting lexical analyzer code.
46.0u 1.0s 0:51 91% 0+0k 0+0io 0pf+0w

vestavia% cat Token.java
// Token class definition
// Token is a class to represent lexical tokens 
// in the PL/0 programming language, described 
// in Algorithms + Data Structures = Programs by
// Niklaus Wirth, Prentice-Hall, 1976.

public class Token {    // token classes

  public static final int EOF       = -1;
  public static final int BEGIN     = 0;
  public static final int CALL      = 1;
  public static final int CONST     = 2;
  public static final int DO        = 3;
  public static final int END       = 4;
  public static final int IF        = 5;
  public static final int ODD       = 6;
  public static final int PROC      = 7;
  public static final int THEN      = 8;
  public static final int VAR       = 9;
  public static final int WHILE     = 10;
  public static final int ID        = 11;
  public static final int INTEGER   = 12;
  public static final int ASSIGN    = 13;
  public static final int PLUS      = '+';
  public static final int MINUS     = '-';
  public static final int TIMES     = '*';
  public static final int SLASH     = '/';
  public static final int EQ        = '=';
  public static final int LT        = '<';
  public static final int GT        = '>';
  public static final int NE        = GT + 1;
  public static final int LE        = NE + 1;
  public static final int GE        = LE + 1;
  public static final int LPAREN    = '(';
  public static final int RPAREN    = ')';
  public static final int COMMA     = ',';
  public static final int PERIOD    = '.';
  public static final int SEMICOLON = ';';

  private int symbol;        // current token
  private String lexeme;     // lexeme

  public Token () { }

  public Token (int symbol) 
  { this (symbol, null); }

  public Token (int symbol, String lexeme) {
    this . symbol = symbol;
    this . lexeme  = lexeme;
  }
  public int symbol () { return symbol; }

  public String lexeme () { return lexeme; }

  public String toString () {
    switch (symbol) {
      case BEGIN :  return "(keyword, begin) ";
      case CALL :   return "(keyword, call) ";
      case CONST :  return "(keyword, const) ";
      case DO :     return "(keyword, do) ";
      case END :    return "(keyword, end) ";
      case IF :     return "(keyword, if) ";
      case ODD :    return "(keyword, odd) ";
      case PROC :   return "(keyword, proc) ";
      case THEN :   return "(keyword, then) ";
      case VAR :    return "(keyword, var) ";
      case WHILE :  return "(keyword, while) ";
      case ASSIGN : return "(operator, :=) ";
      case PLUS :   return "(operator, +) ";
      case MINUS :  return "(operator, -) ";
      case TIMES :  return "(operator, *) ";
      case SLASH :  return "(operator, /) ";
      case EQ :     return "(operator, =) ";
      case LT :     return "(operator, <) ";
      case GT :     return "(operator, >) ";
      case NE :     return "(operator, <>) ";
      case LE :     return "(operator, <=) ";
      case GE :     return "(operator, >=) ";
      case LPAREN : return "(operator, () ";
      case RPAREN : return "(operator, )) ";
      case COMMA :  return "(punctuation, ,) ";
      case PERIOD : return "(punctuation, .) ";
      case SEMICOLON : 
        return "(punctuation, ;) ";
      case ID :
        return "(identifier, " + lexeme + ") ";
      case INTEGER :
        return "(integer, " + lexeme + ") ";
      default :
        ErrorMessage . print (0, 
          "Unrecognized token");
        return null;
    }
  }

}

vestavia% cat ErrorMessage.java
// ErrorMessage class
// This class prints error messages.

public class ErrorMessage {

  public static void print (String message) {
    System . out . println ("***** Error: " + 
      message + " *****");
    System . exit (0);
  }

  public static void print (int position, 
      String message) {
    System . out . println ("");
    for (int i = 0; i < position; i++) 
      System . out . print (" ");
    System . out . println ("^");
    print (message);
  }

}

vestavia% cat PL0Lex.java
// PL0Lex class
// This class is a PL/0 lexical analyzer which 
// reads a PL/0 source program and outputs the 
// list of tokens comprising that program.

public class PL0Lex {

  private static final int MAX_TOKENS = 100;

  public static void main (String [] args) 
      throws java.io.IOException {

    int i, n;
    Token [] token = new Token [MAX_TOKENS];
    Yylex lexer = new Yylex (System . in);

    System . out . println ("Source Program");
    System . out . println ("--------------");
    System . out . println ("");
    n = -1;
    do {
      if (n < MAX_TOKENS)
        token [++n] = lexer . nextToken ();
      else
        ErrorMessage . print (0, 
          "Maximum number of tokens exceeded");
    } while (token[n].symbol() != Token.EOF);

    System . out . println ("");
    System . out . println ("List of Tokens");
    System . out . println ("--------------");
    System . out . println ("");
    for (i = 0; i < n; i++)
      System . out . println (token [i]);
    System . out . println ("");
  }

}

vestavia% java PL0Lex < quotrem.pl0
Source Program
--------------

var q, r, x, y;
begin
    x := 32; y := 5;
    q := 0; r := x;
    while r >= y do begin
        q := q + 1; 
        r := r - y
    end
end.

List of Tokens
--------------

(keyword, var) 
(identifier, q) 
(punctuation, ,) 
(identifier, r) 
(punctuation, ,) 
(identifier, x) 
(punctuation, ,) 
(identifier, y) 
(punctuation, ;) 
(keyword, begin) 
(identifier, x) 
(operator, :=) 
(number, 32) 
(punctuation, ;) 
(identifier, y) 
(operator, :=) 
(number, 5) 
(punctuation, ;) 
(identifier, q) 
(operator, :=) 
(number, 0) 
(punctuation, ;) 
(identifier, r) 
(operator, :=) 
(identifier, x) 
(punctuation, ;) 
(keyword, while) 
(identifier, r) 
(operator, >=) 
(identifier, y) 
(keyword, do)
(keyword, begin) 
(identifier, q) 
(operator, :=) 
(identifier, q) 
(operator, +) 
(integer, 1) 
(punctuation, ;) 
(identifier, r) 
(operator, :=) 
(identifier, r) 
(operator, -) 
(identifier, y) 
(keyword, end) 
(keyword, end) 
(punctuation, .) 
vestavia% exit
script done on Mon Mar 29 09:39:26 1999