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[RFA] Remove restrictions on expanding GLR stacks in C++.
From: |
Paul Hilfinger |
Subject: |
[RFA] Remove restrictions on expanding GLR stacks in C++. |
Date: |
Thu, 29 Jul 2010 15:07:48 -0700 |
Following discussions with Akim and Paul Eggert, I propose the following
patch.
P. Hilfinger
* data/glr.c: Remove tests for __cplusplus related to definition of
YYSTACKEXPANDABLE.
* doc/bison.texinfo: Remove paragraph saying C++ stacks are not
expandable. Reorganize section on GLR semantic values a bit. Remove
discussion of YYLLOC_DEFAULT. Mention restrictions to POD data.
---
data/glr.c | 6 ------
doc/bison.texinfo | 32 ++++++++++++++++++--------------
2 files changed, 18 insertions(+), 20 deletions(-)
diff --git a/data/glr.c b/data/glr.c
index b72aef7..e1c8a45 100644
--- a/data/glr.c
+++ b/data/glr.c
@@ -576,13 +576,7 @@ int yydebug;
#define YYHEADROOM 2
#ifndef YYSTACKEXPANDABLE
-# if (! defined __cplusplus \
- || (]b4_locations_if([[defined YYLTYPE_IS_TRIVIAL && YYLTYPE_IS_TRIVIAL \
- && ]])[defined YYSTYPE_IS_TRIVIAL && YYSTYPE_IS_TRIVIAL))
# define YYSTACKEXPANDABLE 1
-# else
-# define YYSTACKEXPANDABLE 0
-# endif
#endif
#if YYSTACKEXPANDABLE
diff --git a/doc/bison.texinfo b/doc/bison.texinfo
index 6d9d1be..354b733 100644
--- a/doc/bison.texinfo
+++ b/doc/bison.texinfo
@@ -135,7 +135,7 @@ Writing @acronym{GLR} Parsers
* Simple GLR Parsers:: Using @acronym{GLR} parsers on unambiguous grammars.
* Merging GLR Parses:: Using @acronym{GLR} parsers to resolve ambiguities.
-* GLR Semantic Actions:: Deferred semantic actions have special concerns.
+* GLR Semantic Actions:: Considerations for semantic values and deferred
actions.
* Semantic Predicates:: Controlling a parse with arbitrary computations.
* Compiler Requirements:: @acronym{GLR} parsers require a modern C compiler.
@@ -758,7 +758,7 @@ merged result.
@menu
* Simple GLR Parsers:: Using @acronym{GLR} parsers on unambiguous grammars.
* Merging GLR Parses:: Using @acronym{GLR} parsers to resolve ambiguities.
-* GLR Semantic Actions:: Deferred semantic actions have special concerns.
+* GLR Semantic Actions:: Considerations for semantic values and deferred
actions.
* Semantic Predicates:: Controlling a parse with arbitrary computations.
* Compiler Requirements:: @acronym{GLR} parsers require a modern C compiler.
@end menu
@@ -1119,6 +1119,10 @@ the offending merge.
@node GLR Semantic Actions
@subsection GLR Semantic Actions
+The nature of @acronym{GLR} parsing and the structure of the generated
+parsers give rise to certain restrictions on semantic values and actions.
+
address@hidden Deferred semantic actions
@cindex deferred semantic actions
By definition, a deferred semantic action is not performed at the same time as
the associated reduction.
@@ -1152,6 +1156,7 @@ For example, if a semantic action might be deferred, you
should never write it
to invoke @code{yyclearin} (@pxref{Action Features}) or to attempt to free
memory referenced by @code{yylval}.
address@hidden YYERROR
@findex YYERROR
@cindex @acronym{GLR} parsers and @code{YYERROR}
Another Bison feature requiring special consideration is @code{YYERROR}
@@ -1159,11 +1164,17 @@ Another Bison feature requiring special consideration
is @code{YYERROR}
initiate error recovery.
During deterministic @acronym{GLR} operation, the effect of @code{YYERROR} is
the same as its effect in a deterministic parser.
-In a deferred semantic action, its effect is undefined.
address@hidden The effect is probably a syntax error at the split point.
-
-Also, see @ref{Location Default Action, ,Default Action for Locations}, which
-describes a special usage of @code{YYLLOC_DEFAULT} in @acronym{GLR} parsers.
+The effect in a deferred action is similar, but the precise point of the
+error is undefined; instead, the parser reverts to deterministic operation,
+selecting an unspecified stack on which to continue with a syntax error.
+In a semantic predicate (see @ref{Semantic Predicates}) during nondeterministic
+parsing, @code{YYERROR} silently prunes
+the parse that invoked the test.
+
address@hidden Restrictions on semantic values and locations
address@hidden parsers require that you use POD (Plain Old Data) types for
+semantic values and location types when using the generated parsers as
+C++ code.
@node Semantic Predicates
@subsection Controlling a Parse with Arbitrary Predicates
@@ -7388,13 +7399,6 @@ that allows variable-length arrays. The default is 200.
Do not allow @code{YYINITDEPTH} to be greater than @code{YYMAXDEPTH}.
address@hidden FIXME: C++ output.
-Because of semantic differences between C and C++, the deterministic
-parsers in C produced by Bison cannot grow when compiled
-by C++ compilers. In this precise case (compiling a C parser as C++) you are
-suggested to grow @code{YYINITDEPTH}. The Bison maintainers hope to fix
-this deficiency in a future release.
-
@node Error Recovery
@chapter Error Recovery
@cindex error recovery
--
1.7.0.6
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