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Remove restrictions on expanding GLR stacks in C++.

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* data/glr.c:  Remove tests for __cplusplus related to definition of
    YYSTACKEXPANDABLE.
    * doc/bison.texinfo: Rewrite paragraph saying C++ stacks are not
    expandable to instead indicate conditions that prevent their expansion
    in C++.  Reorganize section on GLR semantic values a bit. Remove
    discussion of YYLLOC_DEFAULT. Mention restrictions to POD data.
This commit is contained in:
Paul Hilfinger
2010-07-29 01:43:37 -07:00
parent c61d4fa1d0
commit 20be2f9227
2 changed files with 25 additions and 18 deletions
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37
doc/bison.texinfo
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@@ -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.
@subsubsection 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}.
@subsubsection 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.
@c The effect is probably a syntax error at the split point.
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.
Also, see @ref{Location Default Action, ,Default Action for Locations}, which
describes a special usage of @code{YYLLOC_DEFAULT} in @acronym{GLR} parsers.
@subsubsection Restrictions on semantic values and locations
@acronym{GLR} 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
@@ -7388,12 +7399,14 @@ that allows variable-length arrays. The default is 200.
Do not allow @code{YYINITDEPTH} to be greater than @code{YYMAXDEPTH}.
@c 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.
You can generate a deterministic parser containing C++ user code from
the default (C) skeleton, as well as from the C++ skeleton
(@pxref{C++ Parsers}). However, if you do use the default skeleton
and want to allow the parsing stack to grow,
be careful not to use semantic types or location types that require
non-trivial copy constructors.
The C skeleton bypasses these constructors when copying data to
new, larger stacks.
@node Error Recovery
@chapter Error Recovery