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doc: update GLR sections

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Reported by Christian Schoenebeck.

* doc/bison.texi (GLR Parsers): Minor fixes.
(Compiler Requirements for GLR): Remove, quite useless today.
This commit is contained in:
Akim Demaille
2020-07-14 06:56:15 +02:00
parent 4f9ae5de07
commit 88bd814bf1
1 changed files with 11 additions and 43 deletions
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doc/bison.texi
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@@ -263,7 +263,6 @@ Writing GLR Parsers
* Merging GLR Parses:: Using GLR parsers to resolve ambiguities.
* GLR Semantic Actions:: Considerations for semantic values and deferred actions.
* Semantic Predicates:: Controlling a parse with arbitrary computations.
* Compiler Requirements for GLR:: GLR parsers require a modern C compiler.
Examples
@@ -943,7 +942,6 @@ on the resulting values to produce an arbitrary merged result.
* Merging GLR Parses:: Using GLR parsers to resolve ambiguities.
* GLR Semantic Actions:: Considerations for semantic values and deferred actions.
* Semantic Predicates:: Controlling a parse with arbitrary computations.
* Compiler Requirements for GLR:: GLR parsers require a modern C compiler.
@end menu
@node Simple GLR Parsers
@@ -1372,14 +1370,14 @@ widget:
@noindent
is one way to allow the same parser to handle two different syntaxes for
widgets. The clause preceded by @code{%?} is treated like an ordinary
action, except that its text is treated as an expression and is always
midrule action, except that its text is handled as an expression and is always
evaluated immediately (even when in nondeterministic mode). If the
expression yields 0 (false), the clause is treated as a syntax error,
which, in a nondeterministic parser, causes the stack in which it is reduced
to die. In a deterministic parser, it acts like YYERROR.
to die. In a deterministic parser, it acts like @code{YYERROR}.
As the example shows, predicates otherwise look like semantic actions, and
therefore you must be take them into account when determining the numbers
therefore you must take them into account when determining the numbers
to use for denoting the semantic values of right-hand side symbols.
Predicate actions, however, have no defined value, and may not be given
labels.
@@ -1393,7 +1391,7 @@ widget:
@{ if (!new_syntax) YYERROR; @}
"widget" id new_args @{ $$ = f($3, $4); @}
| @{ if (new_syntax) YYERROR; @}
"widget" id old_args @{ $$ = f($3, $4); @}
"widget" id old_args @{ $$ = f($3, $4); @}
;
@end example
@@ -1411,36 +1409,6 @@ reports an error.
Finally, be careful in writing predicates: deferred actions have not been
evaluated, so that using them in a predicate will have undefined effects.
@node Compiler Requirements for GLR
@subsection Considerations when Compiling GLR Parsers
@cindex @code{inline}
@cindex GLR parsers and @code{inline}
The GLR parsers require a compiler for ISO C89 or
later. In addition, they use the @code{inline} keyword, which is not
C89, but is C99 and is a common extension in pre-C99 compilers. It is
up to the user of these parsers to handle
portability issues. For instance, if using Autoconf and the Autoconf
macro @code{AC_C_INLINE}, a mere
@example
%@{
#include <config.h>
%@}
@end example
@noindent
will suffice. Otherwise, we suggest
@example
%@{
#if (__STDC_VERSION__ < 199901 && ! defined __GNUC__ \
&& ! defined inline)
# define inline
#endif
%@}
@end example
@node Locations
@section Locations
@cindex location
@@ -14824,13 +14792,13 @@ Bison. See the file @file{ABOUT-NLS} for more information.
I can't build Bison because my C compiler is too old.
@end quotation
Except for GLR parsers (@pxref{Compiler Requirements for GLR}), the C
code that Bison generates requires only C89 or later. However, Bison
itself requires common C99 features such as declarations after
statements. Bison's @code{configure} script attempts to enable C99 (or
later) support on compilers that default to pre-C99. If your compiler
lacks these C99 features entirely, GCC may well be a better choice; or
you can try upgrading to your compiler's latest version.
Except for GLR parsers (which require C99), the C code that Bison generates
requires only C89 or later. However, Bison itself requires common C99
features such as declarations after statements. Bison's @code{configure}
script attempts to enable C99 (or later) support on compilers that default
to pre-C99. If your compiler lacks these C99 features entirely, GCC may
well be a better choice; or you can try upgrading to your compiler's latest
version.
@node Where can I find help?
@section Where can I find help?