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Introduce the concept of "weak fallback" in the parser. A weak fallback

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only occurs if a syntax error would result otherwise.

FossilOrigin-Name: c41d7079fb63831bd2f009b64cbf5a423e8119e6b841bfd9bd5a2d85fba3b142
This commit is contained in:
drh
2018-06-28 03:38:49 +00:00
parent 01e1229063
commit 3773c25f16
5 changed files with 54 additions and 29 deletions
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35
tool/lempar.c
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@ -90,6 +90,7 @@
/************* Begin control #defines *****************************************/
%%
/************* End control #defines *******************************************/
#define YY_NLOOKAHEAD ((int)(sizeof(yy_lookahead)/sizeof(yy_lookahead[0])))
/* Define the yytestcase() macro to be a no-op if is not already defined
** otherwise.
@ -172,7 +173,7 @@
** it appears.
*/
#ifdef YYFALLBACK
static const YYCODETYPE yyFallback[] = {
static const int yyFallback[] = {
%%
};
#endif /* YYFALLBACK */
@ -519,24 +520,34 @@ static YYACTIONTYPE yy_find_shift_action(
do{
i = yy_shift_ofst[stateno];
assert( i>=0 );
assert( i+YYNTOKEN<=(int)sizeof(yy_lookahead)/sizeof(yy_lookahead[0]) );
/*assert( i+YYNTOKEN<=YY_NLOOKAHEAD );*/
assert( iLookAhead!=YYNOCODE );
assert( iLookAhead < YYNTOKEN );
i += iLookAhead;
if( yy_lookahead[i]!=iLookAhead ){
if( i>=YY_NLOOKAHEAD || yy_lookahead[i]!=iLookAhead
){
#ifdef YYFALLBACK
YYCODETYPE iFallback; /* Fallback token */
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]);
&& (iFallback = yyFallback[iLookAhead])!=0
){
if( iFallback<0 && yy_default[stateno]==YY_ERROR_ACTION ){
/* A weak fallback only happens if current lookahead is a
** syntax error */
iFallback = -iFallback;
}
if( iFallback>0 ){
/* A strong fallback happens regardless */
#ifndef NDEBUG
if( yyTraceFILE ){
fprintf(yyTraceFILE, "%sFALLBACK %s => %s\n",
yyTracePrompt, yyTokenName[iLookAhead], yyTokenName[iFallback]);
}
#endif
assert( yyFallback[iFallback]==0 ); /* Fallback loop must terminate */
iLookAhead = iFallback;
continue;
assert( yyFallback[iFallback]==0 ); /* Fallback loop must terminate */
iLookAhead = iFallback;
continue;
}
}
#endif
#ifdef YYWILDCARD