Syntax 4.2

---

• Introduction
• Sample Output
• Concepts
  • Lexic
  • Syntax
  • Context Free Languages
  • Top-down, Bottom-up
  • Context Free Grammar
  • Algorithms
• File Structure
  • Structure
  • Meta Symbols
  • Java Example
  • C Example
  • Pascal Example
  • Javascript Example
• Lexer
  • Token Definitions
  • Lexer Code
  • Code Symbols
  • Lexer Modes
  • Disambiguation
  • Writing Your Own Lexer
  • Getting Characters
  • Regular Expressions
• Production Rules
  • Learn by Example
  • Code Generation
  • Intermediate Code
  • Empty Rules
  • Rules Precedence
• Error Management
  • Error Tokens
  • Errors: C Example
  • Errors: Pascal Example
• Lexer Driven Parsing
  • Javascript Example

---

• Syntax Maven Plugin
  • Usage
  • Reference

File Structure

---

• Structure
• Meta Symbols
• Java Example
• C Example
• Pascal Example
• Javascript Example

Structure

%{
  Program declarations
%}

Syntax declarations

%%

Rules

%%

Additional code

The %% markers are present in every syntax file. They delimit the three sections of the file. %{ …%} markers (matched) are completelly optional, and can appear multiple times.

• The program declarations are fragments of code for the native language being used for the output. For example, java files may have the package, import and class declarations. For javascript, it could be the top part of an IIFE (Immediately-Invoked Function Expression.) For Pascal it can be the module or program declaration.
• The syntax declarations declare the terminals, non terminals, error definitions, lexer and other components of the grammar.
• The rules specify the grammar rules by declaring how non terminals are to be constructed.
• The additional code can be anything on the desired target language.
• File extension is usually .sy.

Declaration Meta Symbols

When in the program declaration section, you can use the following meta symbols

Symbol	Description
$$b	The output filename without extensions, no path.
$$n	The output filename with extension, no path
$$f	The output filename with extension and path
$$e	The output filename extension
$$p	The output file’s path, no filename nor extension

Java example

%{
public class TestParser {
%}

%class {
  int number;
    
  public StackElement () {
    this.number = 0;
  }
    
  public String toString() {
    return "n=" + number;
  }
  
  public void setNumber(int number) {
    this.number = number;
  }
}

%lexer = {
  while ($c <= ' ' && $c > '\0') {
    $+;
  }
}

%left             TOK_AND      256:"AND" =  if ($c == '&') {$+; return TOK_AND;};
%left             TOK_OR       257:"OR" =   if ($c == '|') {$+; return TOK_OR;}; 
%right            TOK_NOT      258:"NOT" =  if ($c == '!') {$+; return TOK_NOT;};
%left             TOK_LE       259:"'<='",
                  TOK_LT       260:"'<'",
                  TOK_GE       261:"'>='",
                  TOK_GT       262:"'>'",
                  TOK_NE       263:"'<>'",
                  TOK_EQ       264:"'=='" = {
  if ($c == '=') {
    $+; 
    return TOK_EQ;
  }
  if ($c == '<') {
    $+;
    if ($c == '=') {
      $+;
      return TOK_LE;
    }
    if ($c == '>') {
      $+;
      return TOK_NE;
    }
    return TOK_LT;
  }
  if ($c == '>') {
    $+;
    if ($c == '=') {
      $+;
      return TOK_GE;
    }
    return TOK_GT;
  }  
}

%left             '+' : "plus" =  if ($c == '+') {$+; return '+';};
                , '-' : '"minus"'=  if ($c == '-') {$+; return '-';};
%left             '*' =  if ($c == '*') {$+; return '*';};
                , '/' =  if ($c == '/') {$+; return '/';};

%right            TOK_UMINUS:"unary minus"  

%token            '(' =  if ($c == '(') {$+; return '(';};
                , ')' =  if ($c == ')') {$+; return ')';};

%token   <number> TOK_NUMBER:"number" = {
  if ($c >= '0' && $c <= '9') {
    int number = 0;
    while ($c >= '0' && $c <= '9') {
      number = number * 10 + $c - '0';
      $+;
    }
    lexicalValue.number = number;
    return TOK_NUMBER;
  }
}

%type    <number> Expression

%name Expression : "expression";

%start Expression

%lexer = {
}

%group OPS : "operator" TOK_AND, TOK_OR, TOK_LT, TOK_LE, TOK_GT, TOK_GE, TOK_NE, TOK_EQ, '+', '-', '*', '/';

%%
Expression   :  Expression TOK_AND Expression = $$ = ($1 != 0) && ($3 != 0) ? 1 : 0;
             |  Expression TOK_OR Expression  = $$ = ($1 != 0) || ($3 != 0) ? 1 : 0;
             |  TOK_NOT Expression            = $$ = ($2 != 0) ? 0 : 1;
             |  Expression TOK_LE Expression  = $$ = $1 <= $3 ? 1 : 0;
             |  Expression TOK_LT Expression  = $$ = $1 < $3 ? 1 : 0;
             |  Expression TOK_GE Expression  = $$ = $1 >= $3 ? 1 : 0;
             |  Expression TOK_GT Expression  = $$ = $1 > $3 ? 1 : 0;
             |  Expression TOK_NE Expression  = $$ = $1 != $3 ? 1 : 0;
             |  Expression TOK_EQ Expression  = $$ = $1 == $3 ? 1 : 0;
             |  Expression '+' Expression     = $$ = $1 + $3;
             |  Expression '-' Expression     = $$ = $1 - $3;
             |  Expression '*' Expression     = $$ = $1 * $3;
             |  Expression '/' Expression     = $$ = $1 / $3;
             |  '-' Expression %prec TOK_UMINUS = $$ = -$2;
             |  '(' Expression ')'            = $$ = $2;
             |  TOK_NUMBER
             ;
%%

// END OF GRAMMAR

  int charNum = 0;
  String expression = "(1 + 3) *4 / 5 + -20";
  private char getNextChar(boolean initialize) {
    if (initialize) {
      charNum = 0;
    }
    if (charNum < expression.length()) {
      return expression.charAt(charNum++);
    }
    return EOS;
  }

  private void ungetChar(char c) {
    charNum --;
    if (charNum < 0 || expression.charAt(charNum) != c) {
      throw new RuntimeException("Error putting a character back");
    }
  }

  private int parserError(int state, int token, int top, String message) {
    System.out.println("An error occurred in state " + state + " with token " + token + " on the position " + top);
    System.out.println(message);
    parserPrintStack();
    return ERROR_RE_ATTEMPT;
  }
  
  private String toString(StackElement value) {
    if(value == null) {
      return "";
    } else {
      return value.toString();
    }
  }
  
  public int getTotal() {
    StackElement result = getResult();
    if (result != null) {
      return result.number;
    } else {
      return 0;
    }
  }
  
}

C example

%{
#include <stdio.h>
#include "$$b.h"
%}

%union {
  int number;
}

%lexer = {
  while ($c <= ' ' && $c > '\0') {
    $+;
  }
}

%left             TOK_AND      256:"AND" =  if ($c == '&') {$+; return TOK_AND;};
%left             TOK_OR       257:"OR" =  if ($c == '|') {$+; return TOK_OR;}; 
%right            TOK_NOT      258:"NOT" =  if ($c == '!') {$+; return TOK_NOT;};
%left             TOK_LE       259:"'<='",
                  TOK_LT       260:"'<'",
                  TOK_GE       261:"'>='",
                  TOK_GT       262:"'>'",
                  TOK_NE       263:"'<>'",
                  TOK_EQ       264:"'=='" = {
  if ($c == '=') {
    $+; 
    return TOK_EQ;
  }
  if ($c == '<') {
    $+;
    if ($c == '=') {
      $+;
      return TOK_LE;
    }
    if ($c == '>') {
      $+;
      return TOK_NE;
    }
    return TOK_LT;
  }
  if ($c == '>') {
    $+;
    if ($c == '=') {
      $+;
      return TOK_GE;
    }
    return TOK_GT;
  }  
}

%left             '+' : "plus" =  if ($c == '+') {$+; return '+';};
                , '-' : '"minus"'=  if ($c == '-') {$+; return '-';};
%left             '*' =  if ($c == '*') {$+; return '*';};
                , '/' =  if ($c == '/') {$+; return '/';};

%right            TOK_UMINUS:"unary minus";

%token            '(' =  if ($c == '(') {$+; return '(';};
                , ')' =  if ($c == ')') {$+; return ')';};

%token   <number> TOK_NUMBER:"number" = {
  if ($c >= '0' && $c <= '9') {
    int number = 0;
    while ($c >= '0' && $c <= '9') {
      number = number * 10 + $c - '0';
      $+;
    }
    $v.number = number;
    return TOK_NUMBER;
  }
}

%type    <number> Expression

%start Expression

%lexer = {
}


%%
Expression   :  Expression TOK_AND Expression = $$ = ($1 != 0) && ($3 != 0) ? 1 : 0;
             |  Expression TOK_OR Expression  = $$ = ($1 != 0) || ($3 != 0) ? 1 : 0;
             |  TOK_NOT Expression            = $$ = ($2 != 0) ? 0 : 1;
             |  Expression TOK_LE Expression  = $$ = $1 <= $3 ? 1 : 0;
             |  Expression TOK_LT Expression  = $$ = $1 < $3 ? 1 : 0;
             |  Expression TOK_GE Expression  = $$ = $1 >= $3 ? 1 : 0;
             |  Expression TOK_GT Expression  = $$ = $1 > $3 ? 1 : 0;
             |  Expression TOK_NE Expression  = $$ = $1 != $3 ? 1 : 0;
             |  Expression TOK_EQ Expression  = $$ = $1 == $3 ? 1 : 0;
             |  Expression '+' Expression     = $$ = $1 + $3;
             |  Expression '-' Expression     = $$ = $1 - $3;
             |  Expression '*' Expression     = $$ = $1 * $3;
             |  Expression '/' Expression     = $$ = $1 / $3;
             |  '-' Expression %prec TOK_UMINUS = $$ = -$2;
             |  '(' Expression ')'            = $$ = $2;
             |  TOK_NUMBER
             ;
%%

// END OF GRAMMAR

int charNum = 0;
char * expression = "(1 + 3) *4 / 5 + -20";

char StxNextChar()
{
    if (charNum < strlen(expression)) {
      printf("Char %c\n", expression[charNum]);
      return expression[charNum++];
    }
    return EOS;
}

void StxUngetChar(char c) {
    charNum --;
}

int StxError(int state, int token, int top, char * message)
{
    printf("An error occurred in state %d with token %d on the position %d\n", state, token, top);
    printf("%s\n", message);
#ifdef DEBUG
    StxPrintStack();
#endif
    return ERROR_RE_ATTEMPT;
}

#ifdef DEBUG
char staticToStringValue[1024];

char * StxToString(TSTACK value)
{
    sprintf(staticToStringValue, "%d", value.number);
    return staticToStringValue;
}
#endif
  
int GetTotal() {
    return StxGetResult().number;
}

#ifdef SCANNER_MODE
typedef struct {
    int token;
    int value;
    int result;
    
} PARAMETER, *PPARAMETER;

PARAMETER parameters[] = {
    {'(', 0, 0},
    {TOK_NUMBER, 1, 1},
    {'+', 0, 0},
    {TOK_NUMBER, 3, 3},
    {')', 0, 0},
    {'*', 0, 0},
    {TOK_NUMBER, 4, 4},
    {'/', 0, 0},
    {TOK_NUMBER, 5, 5},
    {'+', 0, 0},
    {'-', 0, 0},
    {TOK_NUMBER, 20, 20},
    {0, 0, -17},
    {-1,0,0}
};

int arrayContains(int *array, int value, int count) {
    int i;
    for (i = 0; i < count; i++) {
        if (array[i] == value) {
            return 1;
        }
    }
    return 0;
}
  
int main(char *argv) 
{
    PPARAMETER p = parameters;
    int count;
    int t;
    TSTACK value;
    
    StxInit();
    
    while (p->token != -1) {
        int *tokens = StxValidTokens(&count);
        if (!arrayContains(tokens, p->token, count)) {
            printf("Token %d ain't there\n", p->token);
            exit (1);
        }
        value.number = p->value;
        if (!StxParse(p->token, value)) {
            printf("Error when parsing symbol %d\n", p->token);
            exit (1);
        }
        t = GetTotal();
        if (t != p->result) {
            printf("Result is not %d\n", p->result);
            exit (1);
        }
        p++;
    }
    t = GetTotal();
    printf("Total: %d\n", t);
    if (t != -17) {
        printf("total does not match\n");
        exit (1);
     }
    exit (0);
}
#else

int main(char *argv) 
{
    if (StxParse()) {
        printf("Total=%d\n", GetTotal());
    }
    exit (0);
}
#endif

Pascal example

%{
{Program that gets compiled and executed by free pascal}
PROGRAM pascaltest;
USES sysutils;
{$I $$b.inc}
{$DEFINE DEBUG}
VAR
    number : LONGINT;
%}

%union
  number:LONGINT;
%

%lexer =
  WHILE ($c = ' ') OR ($c = CHR(9)) DO $+;
  writeln('Char is "', $c, '"');
%

%left             TOK_AND      256:"AND" =  if $c = '&' THEN BEGIN $+; $x(TOK_AND); END;%
%left             TOK_OR       257:"OR"  =  if $c = '|' THEN BEGIN $+; $x(TOK_OR); END;% 
%right            TOK_NOT      258:"NOT" =  if $c = '!' THEN BEGIN $+; $x(TOK_NOT); END;%
%left             TOK_LE       259:"'<='",
                  TOK_LT       260:"'<'",
                  TOK_GE       261:"'>='",
                  TOK_GT       262:"'>'",
                  TOK_NE       263:"'<>'",
                  TOK_EQ       264:"'='" = 
  IF   $c = '='
  THEN BEGIN 
       $+; 
       $x (TOK_EQ);
       END
  ELSE 
  IF   $c = '<'
  THEN BEGIN 
       $+;
       IF   $c = '='
       THEN BEGIN 
            $+;
            $x(TOK_LE);
       END
       ELSE
       IF   $c = '>'
       THEN BEGIN 
            $+;
            $x(TOK_NE);
       END;
       $x(TOK_LT);
  END
  ELSE
  IF   $c = '>'
  THEN BEGIN 
       $+;
       IF   $c = '='
       THEN BEGIN 
            $+;
            $x(TOK_GE);
       END;
       $x(TOK_GT);
       END;
%

%left             '+' : "plus"   =  IF   $c = '+' THEN BEGIN $+; $x(ORD('+')); END;%
                , '-' : '"minus"'=  IF   $c = '-' THEN BEGIN $+; $x(ORD('-')); END;%
%left             '*' =  IF   $c = '*' THEN BEGIN $+; $x(ORD('*')); END;%
                , '/' =  IF   $c = '/' THEN BEGIN $+; $x(ORD('/')); END;%

%right            TOK_UMINUS:"unary minus"  

%token            '(' =  IF   $c = '(' THEN BEGIN $+; $x(ORD('(')); END;%
                , ')' =  IF   $c = ')' THEN BEGIN $+; $x(ORD(')')); END;%

%token   <number> TOK_NUMBER:"number" = 
  IF   ($c >= '0') AND ($c <= '9')
  THEN BEGIN 
       number := 0;
       WHILE ($c >= '0') AND ($c <= '9') DO
             BEGIN 
             number := number * 10 + ORD($c) - ORD('0');
             $+;
             END;
       $v.number := number;
       $x(TOK_NUMBER);
       END;
%

%type    <number> Expression

%start Expression

%lexer = 
%


%%
Expression   :  Expression TOK_AND Expression = IF ($1 <> 0) AND ($3 <> 0) THEN $$ := 1 ELSE $$ := 0;%
             |  Expression TOK_OR Expression  = IF ($1 <> 0) OR ($3 <> 0) THEN $$ := 1 ELSE $$ := 0;%
             |  TOK_NOT Expression            = IF ($2 <> 0) THEN $$ := 0 ELSE $$ := 1;%
             |  Expression TOK_LE Expression  = IF $1 <= $3 THEN $$ := 1 ELSE $$ := 0;%
             |  Expression TOK_LT Expression  = IF $1 < $3 THEN $$ := 1 ELSE $$ := 0;%
             |  Expression TOK_GE Expression  = IF $1 >= $3 THEN $$ := 1 ELSE $$ := 0;%
             |  Expression TOK_GT Expression  = IF $1 > $3 THEN $$ := 1 ELSE $$ := 0;%
             |  Expression TOK_NE Expression  = IF $1 <> $3 THEN $$ := 1 ELSE $$ := 0;%
             |  Expression TOK_EQ Expression  = IF $1 = $3 THEN $$ := 1 ELSE $$ := 0;%
             |  Expression '+' Expression     = $$ := $1 + $3;%
             |  Expression '-' Expression     = $$ := $1 - $3;%
             |  Expression '*' Expression     = $$ := $1 * $3;%
             |  Expression '/' Expression     = $$ := $1 DIV $3;%
             |  '-' Expression %prec TOK_UMINUS = $$ := -$2;%
             |  '(' Expression ')'            = $$ := $2;%
             |  TOK_NUMBER
             ;
%%

// END OF GRAMMAR

VAR
    charNum : INTEGER = 1;

CONST
    expression = '(1 + 3) *4 / 5 + -20';

FUNCTION StxNextChar: CHAR;
BEGIN
    IF   charNum <= LENGTH(expression) 
    THEN BEGIN
         writeln('Char ', expression[charNum]);
         StxNextChar := expression[charNum];
         charNum := charNum + 1;
         END
    ELSE StxNextChar := CHR(EOS);
END;

PROCEDURE StxUngetChar(c:char);
BEGIN
    charNum := charNum - 1;
END;

FUNCTION StxError(StxState:INTEGER; StxSym: INTEGER; pStxStack: INTEGER; aMessage:STRING):INTEGER;
BEGIN
    writeln('An error occurred in state ', StxState, ' with token ', StxSym, ' on the position ', pStxStack);
    writeln(aMessage);
{$IFDEF DEBUG}
    StxPrintStack();
{$ENDIF}
    StxError := ERROR_RE_ATTEMPT;
END;
  
FUNCTION StxToString(value:TSTACK):STRING;
BEGIN
  StxToString := IntToStr(value.number);
END;

FUNCTION GetTotal() :INTEGER; 
BEGIN
    EXIT(StxGetResult().number);
END;

{$IFDEF SCANNER_MODE}
TYPE
  PPARAMETER = ^PARAMETER;
  PARAMETER = RECORD
    token: LongInt;
    value: integer;
    result: integer;
  END;

VAR
  parameters: ARRAY[0..13] OF PARAMETER = (
    (token:ORD('(')  ; value:0; result:0),
    (token:TOK_NUMBER; value:1; result:1),
    (token:ORD('+')  ; value:0; result:0),
    (token:TOK_NUMBER; value:3; result:3),
    (token:ORD(')')  ; value:0; result:0),
    (token:ORD('*')  ; value:0; result:0),
    (token:TOK_NUMBER; value:4; result:4),
    (token:ORD('/')  ; value:0; result:0),
    (token:TOK_NUMBER; value:5; result:5),
    (token:ORD('+')  ; value:0; result:0),
    (token:ORD('-')  ; value:0; result:0),
    (token:TOK_NUMBER; value:20;result: 20),
    (token:0         ; value:0; result:-17),
    (token:-1        ; value:0; result:0));

FUNCTION arrayContains(tokenArray: StxTokenArray; value: INTEGER; count: INTEGER): BOOLEAN; 
VAR
    i: INTEGER;
BEGIN
    FOR i := 0 TO count-1 DO
        IF  tokenArray[i] = value THEN EXIT(TRUE);
    arrayContains := FALSE;
END;

VAR
    count : INTEGER;
    t:INTEGER;
    value:TSTACK;
    validTokens: StxTokenArray;
    i: INTEGER;
BEGIN
    
    StxInit;
    
    i := 0;
    while parameters[i].token <> -1 do
          BEGIN
          validTokens := StxValidTokens(count);
          IF   NOT arrayContains(validTokens, parameters[i].token, count)
          THEN BEGIN
               writeln('Token ', parameters[i].token, ' ain''t there');
               HALT (1);
               END;
          value.number := parameters[i].value;
          IF   StxParse(parameters[i].token, value) = INTERNAL_ERROR
          THEN BEGIN
               writeln('Error when parsing symbol ', parameters[i].token);
               HALT (2);
               END;
          t := GetTotal();
          IF   t <> parameters[i].result
          THEN BEGIN
               writeln('Result is not ', parameters[i].result);
               HALT (3);
               END;
          i := i + 1;
          END;
    t := GetTotal();
    writeln('Total=', t);
    IF   t <> -17 
    THEN BEGIN
         writeln('total does not match');
         HALT (4);
         END;
END.
{$ELSE}
BEGIN
    IF   StxParse() THEN writeln('Total=', GetTotal);
END.
{$ENDIF}

Javascript example

%{
if (!console) { // i.e. nashorn
    var console = { log: print };
}

var calc = (function() {
%}

%class {
    this.number = 0;
    
    this.toString = function() {
        return "number=" + this.number;
    }
}

%lexer = {
    while ($c <= ' ' && $c > '\0') {
        $+;
    }
}

%left             TOK_AND      256:"AND"       = if ($c == '&') {$+; return TOK_AND.charCodeAt(0);};
%left             TOK_OR       257:"OR"        = if ($c == '|') {$+; return TOK_OR.charCodeAt(0);}; 
%right            TOK_NOT      258:"NOT"       = if ($c == '!') {$+; return TOK_NOT.charCodeAt(0);};
%left             TOK_LE       259:"'<='" /<=/ = return TOK_LE.charCodeAt(0);
     ,            TOK_LT       260:"'<'"  /</  = return TOK_LT.charCodeAt(0);
     ,            TOK_GE       261:"'>='" />=/ = return TOK_GE.charCodeAt(0);
     ,            TOK_GT       262:"'>'"  />/  = return TOK_GT.charCodeAt(0);
     ,            TOK_NE       263:"'<>'" /<>/ = return TOK_NE.charCodeAt(0);
     ,            TOK_EQ       264:"'='"  /=/  = return TOK_EQ.charCodeAt(0);

%left             '+' : "plus"                 = if ($c == '+') {$+; return '+'.charCodeAt(0);};
                , '-' : '"minus"'              = if ($c == '-') {$+; return '-'.charCodeAt(0);};
%left             '*'                          = if ($c == '*') {$+; return '*'.charCodeAt(0);};
                , '/'                          = if ($c == '/') {$+; return '/'.charCodeAt(0);};

%right            TOK_UMINUS:"unary minus"  

%token            '('                          = if ($c == '(') {$+; return '('.charCodeAt(0);};
                , ')'                          = if ($c == ')') {$+; return ')'.charCodeAt(0);};

%token <number> TOK_NUMBER : "number" /[0-9]*/ = {
    $v.number = parseInt($r);
    return TOK_NUMBER;
}

%type    <number> Expression

%name Expression : "expression";

%start Expression

%lexer = {
}

%group OPS : "operator" TOK_AND, TOK_OR, TOK_LT, TOK_LE, TOK_GT, TOK_GE, TOK_NE, TOK_EQ, '+', '-', '*', '/';

%%
Expression   :  Expression TOK_AND Expression = $$ = ($1 != 0) && ($3 != 0) ? 1 : 0;
             |  Expression TOK_OR Expression  = $$ = ($1 != 0) || ($3 != 0) ? 1 : 0;
             |  TOK_NOT Expression            = $$ = ($2 != 0) ? 0 : 1;
             |  Expression TOK_LE Expression  = $$ = $1 <= $3 ? 1 : 0;
             |  Expression TOK_LT Expression  = $$ = $1 < $3 ? 1 : 0;
             |  Expression TOK_GE Expression  = $$ = $1 >= $3 ? 1 : 0;
             |  Expression TOK_GT Expression  = $$ = $1 > $3 ? 1 : 0;
             |  Expression TOK_NE Expression  = $$ = $1 != $3 ? 1 : 0;
             |  Expression TOK_EQ Expression  = $$ = $1 == $3 ? 1 : 0;
             |  Expression '+' Expression     = $$ = $1 + $3;
             |  Expression '-' Expression     = $$ = $1 - $3;
             |  Expression '*' Expression     = $$ = $1 * $3;
             |  Expression '/' Expression     = $$ = $1 / $3;
             |  '-' Expression %prec TOK_UMINUS = $$ = -$2;
             |  '(' Expression ')'            = $$ = $2;
             |  TOK_NUMBER
             ;
%%

// END OF GRAMMAR

    var charNum = 0;
    var expression = "(1 + 3) *4 / 5 + 20";

    function getNextChar(initialize) {
        if (initialize) {
            charNum = 0;
        }
        if (charNum < expression.length) {
            return expression.charAt(charNum++);
        }
        return '\0';
    }

    function ungetChar(c) {
        charNum --;
        if (charNum < 0 || expression.charAt(charNum) != c) {
            throw new Error("Error putting a character back");
        }
    }

    function parserError(state, token, top, message) {
        console.log("An error occurred in position " + charNum + " with token " + getTokenName(token));
        console.log(message);
        return ERROR_RE_ATTEMPT;
    }

    return {
        setVerbose: setVerbose,
        getTokenName: getTokenName,
        getTokenFullName: getTokenFullName,
        getTokenIndex: getTokenIndex,
        scanner: parserElement,
        parse: parse,
        scanner: function (token, value) {
            var lexicalValue = new StackElement();
            lexicalValue.number = value;
            var numericToken;
        
            if (typeof token == 'number') {
                numericToken = token;
            }
            else {
                numericToken = token.charCodeAt(0);
            }
            return parse(numericToken, lexicalValue);
        },
        dumpTokens: dumpTokens,
        init: init,
        getValidTokens: getValidTokens,
        getResult: getResult
    }
 
})();

var calculate = function () {
    calc.parse();
    return 'The result is ' + calc.getResult().number;
}

// Scanner based routines
var init = function () {
    calc.init();
}

var parse = function(token, value) {
    return calc.scanner(token, value);
}

var getValidTokens = function() {
    return calc.getValidTokens().sort(function (a, b) {
        return a - b;
    }).join(",");
}

var getResult = function() {
    return calc.getResult().number;
}