diff options
Diffstat (limited to 'NEWS')
| -rw-r--r-- | NEWS | 44 |
1 files changed, 22 insertions, 22 deletions
@@ -57,27 +57,27 @@ Bison News %define lr.type ielr %define lr.type canonical-lr - The default reduction optimization in the parser tables can also be - adjusted using `%define lr.default-reductions'. See the documentation - for `%define lr.type' and `%define lr.default-reductions' in the - section `Bison Declaration Summary' in the Bison manual for the - details. + The default-reduction optimization in the parser tables can also be + adjusted using `%define lr.default-reductions'. For details on both + of these features, see the new section `Tuning LR' in the Bison + manual. These features are experimental. More user feedback will help to stabilize them. -** LAC (lookahead correction) for syntax error handling: +** LAC (Lookahead Correction) for syntax error handling: Canonical LR, IELR, and LALR can suffer from a couple of problems upon encountering a syntax error. First, the parser might perform additional parser stack reductions before discovering the syntax - error. Such reductions perform user semantic actions that are + error. Such reductions can perform user semantic actions that are unexpected because they are based on an invalid token, and they cause error recovery to begin in a different syntactic context than the one in which the invalid token was encountered. Second, when - verbose error messages are enabled (with %error-verbose or `#define - YYERROR_VERBOSE'), the expected token list in the syntax error - message can both contain invalid tokens and omit valid tokens. + verbose error messages are enabled (with %error-verbose or the + obsolete `#define YYERROR_VERBOSE'), the expected token list in the + syntax error message can both contain invalid tokens and omit valid + tokens. The culprits for the above problems are %nonassoc, default reductions in inconsistent states, and parser state merging. Thus, @@ -85,11 +85,11 @@ Bison News %nonassoc is used or if default reductions are enabled for inconsistent states. - LAC is a new mechanism within the parsing algorithm that completely - solves these problems for canonical LR, IELR, and LALR without - sacrificing %nonassoc, default reductions, or state mering. When - LAC is in use, canonical LR and IELR behave exactly the same for - both syntactically acceptable and syntactically unacceptable input. + LAC is a new mechanism within the parsing algorithm that solves + these problems for canonical LR, IELR, and LALR without sacrificing + %nonassoc, default reductions, or state merging. When LAC is in + use, canonical LR and IELR behave almost exactly the same for both + syntactically acceptable and syntactically unacceptable input. While LALR still does not support the full language-recognition power of canonical LR and IELR, LAC at least enables LALR's syntax error handling to correctly reflect LALR's language-recognition @@ -100,8 +100,8 @@ Bison News %define parse.lac full - See the documentation for `%define parse.lac' in the section `Bison - Declaration Summary' in the Bison manual for additional details. + See the new section `LAC' in the Bison manual for additional + details including a few caveats. LAC is an experimental feature. More user feedback will help to stabilize it. @@ -255,11 +255,11 @@ Bison News ** Verbose syntax error message fixes: - When %error-verbose or `#define YYERROR_VERBOSE' is specified, - syntax error messages produced by the generated parser include the - unexpected token as well as a list of expected tokens. The effect - of %nonassoc on these verbose messages has been corrected in two - ways, but a complete fix requires LAC, described above: + When %error-verbose or the obsolete `#define YYERROR_VERBOSE' is + specified, syntax error messages produced by the generated parser + include the unexpected token as well as a list of expected tokens. + The effect of %nonassoc on these verbose messages has been corrected + in two ways, but a more complete fix requires LAC, described above: *** When %nonassoc is used, there can exist parser states that accept no tokens, and so the parser does not always require a lookahead token |