SQLite

the type of the third argument is integer, but the grammar will
usually redefine this type to be some kind of structure.
Typically the second argument will be a broad category of tokens
such as ``identifier'' or ``number'' and the third argument will
be the name of the identifier or the value of the number.</p>

<p>The Parse() function may have either three or four arguments,
depending on the grammar.  If the grammar specification file requests
it (via the <a href='#extraarg'><tt>extra_argument</tt> directive</a>),
the Parse() function will have a fourth parameter that can be
of any type chosen by the programmer.  The parser doesn't do anything
with this argument except to pass it through to action routines.
This is a convenient mechanism for passing state information down
to the action routines without having to use global variables.</p>

<p>A typical use of a Lemon parser might look something like the
following:

<li>Lemon allows multiple parsers to be running simultaneously.  Yacc
    and bison do not.
</ul>
These differences may cause some initial confusion for programmers
with prior yacc and bison experience.
But after years of experience using Lemon, I firmly
believe that the Lemon way of doing things is better.</p>

<p><i>Updated as of 2016-02-16:</i>
The text above was written in the 1990s.
We are told that Bison has lately been enhanced to support the
tokenizer-calls-parser paradigm used by Lemon, and to obviate the
need for global variables.</p>

<h2>Input File Syntax</h2>

<p>The main purpose of the grammar specification file for Lemon is
to define the grammar for the parser.  But the input file also
specifies additional information Lemon requires to do its job.
Most of the work in using Lemon is in writing an appropriate

the destructor is not called in this circumstance.</p>

<p>By appropriate use of destructors, it is possible to
build a parser using Lemon that can be used within a long-running
program, such as a GUI, that will not leak memory or other resources.
To do the same using yacc or bison is much more difficult.</p>

<a name="extraarg"></a>
<h4>The <tt>%extra_argument</tt> directive</h4>

The %extra_argument directive instructs Lemon to add a 4th parameter
to the parameter list of the Parse() function it generates.  Lemon
doesn't do anything itself with this extra argument, but it does
make the argument available to C-code action routines, destructors,
and so forth.  For example, if the grammar file contains:</p>

%syntax_error {
  UNUSED_PARAM(yymajor); /* Silence a compiler warning */
  sqlite3Fts5ParseError(
    pParse, "fts5: syntax error near \"%.*s\"",TOKEN.n,TOKEN.p
  );
}
%stack_overflow {

  sqlite3Fts5ParseError(pParse, "fts5: parser stack overflow");
}

// The name of the generated procedure that implements the parser
// is as follows:
%name sqlite3Fts5Parser

//
%syntax_error {
  UNUSED_PARAMETER(yymajor);  /* Silence some compiler warnings */
  assert( TOKEN.z[0] );  /* The tokenizer always gives us a token */
  sqlite3ErrorMsg(pParse, "near \"%T\": syntax error", &TOKEN);
}
%stack_overflow {

  sqlite3ErrorMsg(pParse, "parser stack overflow");
}

// The name of the generated procedure that implements the parser
// is as follows:
%name sqlite3Parser

#endif
  return yy_action[i];
}

/*
** The following routine is called if the stack overflows.
*/
static void yyStackOverflow(yyParser *yypParser){
   ParseARG_FETCH;
   yypParser->yyidx--;
#ifndef NDEBUG
   if( yyTraceFILE ){
     fprintf(yyTraceFILE,"%sStack Overflow!\n",yyTracePrompt);
   }
#endif

/*
** Perform a shift action.
*/
static void yy_shift(
  yyParser *yypParser,          /* The parser to be shifted */
  int yyNewState,               /* The new state to shift in */
  int yyMajor,                  /* The major token to shift in */
  ParseTOKENTYPE yyMinor        /* The minor token to shift in */
){
  yyStackEntry *yytos;
  yypParser->yyidx++;
#ifdef YYTRACKMAXSTACKDEPTH
  if( yypParser->yyidx>yypParser->yyidxMax ){
    yypParser->yyidxMax = yypParser->yyidx;
  }
#endif
#if YYSTACKDEPTH>0 
  if( yypParser->yyidx>=YYSTACKDEPTH ){
    yyStackOverflow(yypParser);
    return;
  }
#else
  if( yypParser->yyidx>=yypParser->yystksz ){
    yyGrowStack(yypParser);
    if( yypParser->yyidx>=yypParser->yystksz ){
      yyStackOverflow(yypParser);
      return;
    }
  }
#endif
  yytos = &yypParser->yystack[yypParser->yyidx];
  yytos->stateno = (YYACTIONTYPE)yyNewState;
  yytos->major = (YYCODETYPE)yyMajor;
  yytos->minor.yy0 = yyMinor;
  yyTraceShift(yypParser, yyNewState);
}

/* The following table contains information about every rule that
** is used during the reduce.
*/
static const struct {

  if( yyTraceFILE && yyruleno>=0 
        && yyruleno<(int)(sizeof(yyRuleName)/sizeof(yyRuleName[0])) ){
    yysize = yyRuleInfo[yyruleno].nrhs;
    fprintf(yyTraceFILE, "%sReduce [%s], go to state %d.\n", yyTracePrompt,
      yyRuleName[yyruleno], yymsp[-yysize].stateno);
  }
#endif /* NDEBUG */
  /*  yygotominor = yyzerominor; */

  /* Check that the stack is large enough to grow by a single entry
  ** if the RHS of the rule is empty.  This ensures that there is room
  ** enough on the stack to push the LHS value */
  if( yyRuleInfo[yyruleno].nrhs==0 ){
#ifdef YYTRACKMAXSTACKDEPTH
    if( yypParser->yyidx>yypParser->yyidxMax ){
      yypParser->yyidxMax = yypParser->yyidx;
    }
#endif
#if YYSTACKDEPTH>0 
    if( yypParser->yyidx>=YYSTACKDEPTH ){
      yyStackOverflow(yypParser);
      return;
    }
#else
    if( yypParser->yyidx>=yypParser->yystksz ){
      yyGrowStack(yypParser);
      if( yypParser->yyidx>=yypParser->yystksz ){
        yyStackOverflow(yypParser);
        return;
      }
    }
#endif
  }

  switch( yyruleno ){
  /* Beginning here are the reduction cases.  A typical example
  ** follows:
  **   case 0:
  **  #line <lineno> <grammarfile>
  **     { ... }           // User supplied code
  **  #line <lineno> <thisfile>
  **     break;
  */
/********** Begin reduce actions **********************************************/
%%
/********** End reduce actions ************************************************/
  };
  assert( yyruleno>=0 && yyruleno<sizeof(yyRuleInfo)/sizeof(yyRuleInfo[0]) );
  yygoto = yyRuleInfo[yyruleno].lhs;
  yysize = yyRuleInfo[yyruleno].nrhs;

  yyact = yy_find_reduce_action(yymsp[-yysize].stateno,(YYCODETYPE)yygoto);
  if( yyact <= YY_MAX_SHIFTREDUCE ){
    if( yyact>YY_MAX_SHIFT ) yyact += YY_MIN_REDUCE - YY_MIN_SHIFTREDUCE;





    yypParser->yyidx -= yysize - 1;
    yymsp -= yysize-1;
    yymsp->stateno = (YYACTIONTYPE)yyact;
    yymsp->major = (YYCODETYPE)yygoto;
    yymsp->minor = yygotominor;
    yyTraceShift(yypParser, yyact);
  }else{



    assert( yyact == YY_ACCEPT_ACTION );
    yypParser->yyidx -= yysize;
    yy_accept(yypParser);
  }
}

/*
** The following code executes when the parse fails
*/

/*
** The following code executes when a syntax error first occurs.
*/
static void yy_syntax_error(
  yyParser *yypParser,           /* The parser */
  int yymajor,                   /* The major type of the error token */
  ParseTOKENTYPE yyminor         /* The minor type of the error token */
){
  ParseARG_FETCH;
#define TOKEN yyminor
/************ Begin %syntax_error code ****************************************/
%%
/************ End %syntax_error code ******************************************/
  ParseARG_STORE; /* Suppress warning about unused %extra_argument variable */
}

/*

  yyParser *yypParser;  /* The parser */

  /* (re)initialize the parser, if necessary */
  yypParser = (yyParser*)yyp;
  if( yypParser->yyidx<0 ){
#if YYSTACKDEPTH<=0
    if( yypParser->yystksz <=0 ){


      yyStackOverflow(yypParser);
      return;
    }
#endif
    yypParser->yyidx = 0;
#ifndef YYNOERRORRECOVERY
    yypParser->yyerrcnt = -1;
#endif
    yypParser->yystack[0].stateno = 0;
    yypParser->yystack[0].major = 0;
#ifndef NDEBUG
    if( yyTraceFILE ){
      fprintf(yyTraceFILE,"%sInitialize. Empty stack. State 0\n",
              yyTracePrompt);
    }
#endif
  }

#if !defined(YYERRORSYMBOL) && !defined(YYNOERRORRECOVERY)
  yyendofinput = (yymajor==0);
#endif
  ParseARG_STORE;

#ifndef NDEBUG
  if( yyTraceFILE ){
    fprintf(yyTraceFILE,"%sInput '%s'\n",yyTracePrompt,yyTokenName[yymajor]);
  }
#endif

  do{
    yyact = yy_find_shift_action(yypParser,(YYCODETYPE)yymajor);
    if( yyact <= YY_MAX_SHIFTREDUCE ){
      if( yyact > YY_MAX_SHIFT ) yyact += YY_MIN_REDUCE - YY_MIN_SHIFTREDUCE;
      yy_shift(yypParser,yyact,yymajor,yyminor);
#ifndef YYNOERRORRECOVERY
      yypParser->yyerrcnt--;
#endif
      yymajor = YYNOCODE;
    }else if( yyact <= YY_MAX_REDUCE ){
      yy_reduce(yypParser,yyact-YY_MIN_REDUCE);
    }else{
      assert( yyact == YY_ERROR_ACTION );
      yyminorunion.yy0 = yyminor;
#ifdef YYERRORSYMBOL
      int yymx;
#endif
#ifndef NDEBUG
      if( yyTraceFILE ){
        fprintf(yyTraceFILE,"%sSyntax Error!\n",yyTracePrompt);
      }

      **
      **  * Begin accepting and shifting new tokens.  No new error
      **    processing will occur until three tokens have been
      **    shifted successfully.
      **
      */
      if( yypParser->yyerrcnt<0 ){
        yy_syntax_error(yypParser,yymajor,yyminor);
      }
      yymx = yypParser->yystack[yypParser->yyidx].major;
      if( yymx==YYERRORSYMBOL || yyerrorhit ){
#ifndef NDEBUG
        if( yyTraceFILE ){
          fprintf(yyTraceFILE,"%sDiscard input token %s\n",
             yyTracePrompt,yyTokenName[yymajor]);
        }
#endif
        yy_destructor(yypParser, (YYCODETYPE)yymajor, &yyminorunion);
        yymajor = YYNOCODE;
      }else{
        while(
          yypParser->yyidx >= 0 &&
          yymx != YYERRORSYMBOL &&
          (yyact = yy_find_reduce_action(
                        yypParser->yystack[yypParser->yyidx].stateno,
                        YYERRORSYMBOL)) >= YY_MIN_REDUCE
        ){
          yy_pop_parser_stack(yypParser);
        }
        if( yypParser->yyidx < 0 || yymajor==0 ){
          yy_destructor(yypParser,(YYCODETYPE)yymajor,&yyminorunion);
          yy_parse_failed(yypParser);
          yymajor = YYNOCODE;
        }else if( yymx!=YYERRORSYMBOL ){


          yy_shift(yypParser,yyact,YYERRORSYMBOL,yyminor);
        }
      }
      yypParser->yyerrcnt = 3;
      yyerrorhit = 1;
#elif defined(YYNOERRORRECOVERY)
      /* If the YYNOERRORRECOVERY macro is defined, then do not attempt to
      ** do any kind of error recovery.  Instead, simply invoke the syntax
      ** error routine and continue going as if nothing had happened.
      **
      ** Applications can set this macro (for example inside %include) if
      ** they intend to abandon the parse upon the first syntax error seen.
      */
      yy_syntax_error(yypParser,yymajor, yyminor);
      yy_destructor(yypParser,(YYCODETYPE)yymajor,&yyminorunion);
      yymajor = YYNOCODE;
      
#else  /* YYERRORSYMBOL is not defined */
      /* This is what we do if the grammar does not define ERROR:
      **
      **  * Report an error message, and throw away the input token.
      **
      **  * If the input token is $, then fail the parse.
      **
      ** As before, subsequent error messages are suppressed until
      ** three input tokens have been successfully shifted.
      */
      if( yypParser->yyerrcnt<=0 ){
        yy_syntax_error(yypParser,yymajor, yyminor);
      }
      yypParser->yyerrcnt = 3;
      yy_destructor(yypParser,(YYCODETYPE)yymajor,&yyminorunion);
      if( yyendofinput ){
        yy_parse_failed(yypParser);
      }
      yymajor = YYNOCODE;