[antlr-interest] whether antlr supports the yyfallback function to reuse the keyword as identifier
service
service at sharpplus.com
Wed Apr 18 07:34:26 PDT 2007
Dear friends
I am a newbaby of antlr, now I want to know whether antlr supports the yyfallback function to reuse the keyword as identifier, like the following sqlite parser:
/* The next table maps tokens into fallback tokens. If a construct
** like the following:
**
** %fallback ID X Y Z.
**
** appears in the grammer, then ID becomes a fallback token for X, Y,
** and Z. Whenever one of the tokens X, Y, or Z is input to the parser
** but it does not parse, the type of the token is changed to ID and
** the parse is retried before an error is thrown.
*/
#ifdef YYFALLBACK
static const YYCODETYPE yyFallback[] = {
0, /* $ => nothing */
0, /* SEMI => nothing */
23, /* EXPLAIN => ID */
23, /* QUERY => ID */
23, /* PLAN => ID */
....
}
static int yy_find_shift_action(
yyParser *pParser, /* The parser */
YYCODETYPE iLookAhead /* The look-ahead token */
){
int i;
int stateno = pParser->yystack[pParser->yyidx].stateno;
if( stateno>YY_SHIFT_MAX || (i = yy_shift_ofst[stateno])==YY_SHIFT_USE_DFLT ){
return yy_default[stateno];
}
if( iLookAhead==YYNOCODE ){
return YY_NO_ACTION;
}
i += iLookAhead;
if( i<0 || i>=YY_SZ_ACTTAB || yy_lookahead[i]!=iLookAhead ){
if( iLookAhead>0 ){
#ifdef YYFALLBACK
int iFallback; /* Fallback token */
if( iLookAhead<sizeof(yyFallback)/sizeof(yyFallback[0])
&& (iFallback = yyFallback[iLookAhead])!=0 ){
#ifndef NDEBUG
if( yyTraceFILE ){
fprintf(yyTraceFILE, "%sFALLBACK %s => %s\n",
yyTracePrompt, yyTokenName[iLookAhead], yyTokenName[iFallback]);
}
#endif
return yy_find_shift_action(pParser, iFallback);
}
#endif
#ifdef YYWILDCARD
{
int j = i - iLookAhead + YYWILDCARD;
if( j>=0 && j<YY_SZ_ACTTAB && yy_lookahead[j]==YYWILDCARD ){
#ifndef NDEBUG
if( yyTraceFILE ){
fprintf(yyTraceFILE, "%sWILDCARD %s => %s\n",
yyTracePrompt, yyTokenName[iLookAhead], yyTokenName[YYWILDCARD]);
}
#endif /* NDEBUG */
return yy_action[j];
}
}
#endif /* YYWILDCARD */
}
return yy_default[stateno];
}else{
return yy_action[i];
}
}
Thanks in advance
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