* 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.
@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
@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.
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}
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.
-
-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.
+
+@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
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