Future/bison
1
0
Fork 0
mirror of https://git.savannah.gnu.org/git/bison.git synced 2026-03-09 20:33:03 +00:00
Code Issues Packages Projects Releases Wiki Activity

Minor spelling and typographical fixes. Use @acronym consistently.

Browse Source 
Standardize on "Yacc" instead of "YACC", "Algol" instead of "ALGOL".
Give a bit more history about BNF.
This commit is contained in:
Paul Eggert
2002-10-23 05:26:32 +00:00
parent 6db10d14be
commit c827f760f6
1 changed files with 153 additions and 127 deletions
Download Patch File Download Diff File Expand all files Collapse all files

280
doc/bison.texinfo
View File

@@ -36,30 +36,31 @@
@copying
This manual is for GNU Bison (version @value{VERSION}, @value{UPDATED}),
the GNU parser generator.
This manual is for @acronym{GNU} Bison (version @value{VERSION},
@value{UPDATED}), the @acronym{GNU} parser generator.
Copyright @copyright{} 1988, 1989, 1990, 1991, 1992, 1993, 1995, 1998,
1999, 2000, 2001, 2002 Free Software Foundation, Inc.
@quotation
Permission is granted to copy, distribute and/or modify this document
under the terms of the GNU Free Documentation License, Version 1.1 or
any later version published by the Free Software Foundation; with no
Invariant Sections, with the Front-Cover texts being ``A GNU Manual,''
and with the Back-Cover Texts as in (a) below. A copy of the
license is included in the section entitled ``GNU Free Documentation
License.''
under the terms of the @acronym{GNU} Free Documentation License,
Version 1.1 or any later version published by the Free Software
Foundation; with no Invariant Sections, with the Front-Cover texts
being ``A @acronym{GNU} Manual,'' and with the Back-Cover Texts as in
(a) below. A copy of the license is included in the section entitled
``@acronym{GNU} Free Documentation License.''
(a) The FSF's Back-Cover Text is: ``You have freedom to copy and modify
this GNU Manual, like GNU software. Copies published by the Free
Software Foundation raise funds for GNU development.''
(a) The @acronym{FSF}'s Back-Cover Text is: ``You have freedom to copy
and modify this @acronym{GNU} Manual, like @acronym{GNU} software.
Copies published by the Free Software Foundation raise funds for
@acronym{GNU} development.''
@end quotation
@end copying
@dircategory GNU programming tools
@direntry
* bison: (bison). GNU parser generator (yacc replacement).
* bison: (bison). @acronym{GNU} parser generator (Yacc replacement).
@end direntry
@ifset shorttitlepage-enabled
@@ -67,7 +68,7 @@ Software Foundation raise funds for GNU development.''
@end ifset
@titlepage
@title Bison
@subtitle The YACC-compatible Parser Generator
@subtitle The Yacc-compatible Parser Generator
@subtitle @value{UPDATED}, Bison Version @value{VERSION}
@author by Charles Donnelly and Richard Stallman
@@ -80,7 +81,7 @@ Published by the Free Software Foundation @*
59 Temple Place, Suite 330 @*
Boston, MA 02111-1307 USA @*
Printed copies are available from the Free Software Foundation.@*
ISBN 1-882114-44-2
@acronym{ISBN} 1-882114-44-2
@sp 2
Cover art by Etienne Suvasa.
@end titlepage
@@ -96,7 +97,7 @@ Cover art by Etienne Suvasa.
@menu
* Introduction::
* Conditions::
* Copying:: The GNU General Public License says
* Copying:: The @acronym{GNU} General Public License says
how you can copy and share Bison
Tutorial sections:
@@ -265,9 +266,9 @@ Understanding or Debugging Your Parser
Invoking Bison
* Bison Options:: All the options described in detail,
in alphabetical order by short options.
in alphabetical order by short options.
* Option Cross Key:: Alphabetical list of long options.
* VMS Invocation:: Bison command syntax on VMS.
* VMS Invocation:: Bison command syntax on @acronym{VMS}.
Frequently Asked Questions
@@ -285,7 +286,7 @@ Copying This Manual
@cindex introduction
@dfn{Bison} is a general-purpose parser generator that converts a
grammar description for an LALR(1) context-free grammar into a C
grammar description for an @acronym{LALR}(1) context-free grammar into a C
program to parse that grammar. Once you are proficient with Bison,
you may use it to develop a wide range of language parsers, from those
used in simple desk calculators to complex programming languages.
@@ -311,10 +312,11 @@ This edition corresponds to version @value{VERSION} of Bison.
As of Bison version 1.24, we have changed the distribution terms for
@code{yyparse} to permit using Bison's output in nonfree programs when
Bison is generating C code for LALR(1) parsers. Formerly, these
Bison is generating C code for @acronym{LALR}(1) parsers. Formerly, these
parsers could be used only in programs that were free software.
The other GNU programming tools, such as the GNU C compiler, have never
The other @acronym{GNU} programming tools, such as the @acronym{GNU} C
compiler, have never
had such a requirement. They could always be used for nonfree
software. The reason Bison was different was not due to a special
policy decision; it resulted from applying the usual General Public
@@ -324,7 +326,8 @@ The output of the Bison utility---the Bison parser file---contains a
verbatim copy of a sizable piece of Bison, which is the code for the
@code{yyparse} function. (The actions from your grammar are inserted
into this function at one point, but the rest of the function is not
changed.) When we applied the GPL terms to the code for @code{yyparse},
changed.) When we applied the @acronym{GPL} terms to the code for
@code{yyparse},
the effect was to restrict the use of Bison output to free software.
We didn't change the terms because of sympathy for people who want to
@@ -332,10 +335,11 @@ make software proprietary. @strong{Software should be free.} But we
concluded that limiting Bison's use to free software was doing little to
encourage people to make other software free. So we decided to make the
practical conditions for using Bison match the practical conditions for
using the other GNU tools.
using the other @acronym{GNU} tools.
This exception applies only when Bison is generating C code for a
LALR(1) parser; otherwise, the GPL terms operate as usual. You can
@acronym{LALR}(1) parser; otherwise, the @acronym{GPL} terms operate
as usual. You can
tell whether the exception applies to your @samp{.c} output file by
inspecting it to see whether it says ``As a special exception, when
this file is copied by Bison into a Bison output file, you may use
@@ -381,32 +385,35 @@ can be made of a minus sign and another expression''. Another would be,
recursive, but there must be at least one rule which leads out of the
recursion.
@cindex BNF
@cindex @acronym{BNF}
@cindex Backus-Naur form
The most common formal system for presenting such rules for humans to read
is @dfn{Backus-Naur Form} or ``BNF'', which was developed in order to
specify the language Algol 60. Any grammar expressed in BNF is a
context-free grammar. The input to Bison is essentially machine-readable
BNF.
is @dfn{Backus-Naur Form} or ``@acronym{BNF}'', which was developed in
order to specify the language Algol 60. Any grammar expressed in
@acronym{BNF} is a context-free grammar. The input to Bison is
essentially machine-readable @acronym{BNF}.
@cindex LALR(1) grammars
@cindex LR(1) grammars
@cindex @acronym{LALR}(1) grammars
@cindex @acronym{LR}(1) grammars
There are various important subclasses of context-free grammar. Although it
can handle almost all context-free grammars, Bison is optimized for what
are called LALR(1) grammars.
are called @acronym{LALR}(1) grammars.
In brief, in these grammars, it must be possible to
tell how to parse any portion of an input string with just a single
token of look-ahead. Strictly speaking, that is a description of an
LR(1) grammar, and LALR(1) involves additional restrictions that are
@acronym{LR}(1) grammar, and @acronym{LALR}(1) involves additional
restrictions that are
hard to explain simply; but it is rare in actual practice to find an
LR(1) grammar that fails to be LALR(1). @xref{Mystery Conflicts, ,
Mysterious Reduce/Reduce Conflicts}, for more information on this.
@acronym{LR}(1) grammar that fails to be @acronym{LALR}(1).
@xref{Mystery Conflicts, ,Mysterious Reduce/Reduce Conflicts}, for
more information on this.
@cindex GLR parsing
@cindex generalized LR (GLR) parsing
@cindex @acronym{GLR} parsing
@cindex generalized @acronym{LR} (@acronym{GLR}) parsing
@cindex ambiguous grammars
@cindex non-deterministic parsing
Parsers for LALR(1) grammars are @dfn{deterministic}, meaning roughly that
Parsers for @acronym{LALR}(1) grammars are @dfn{deterministic},
meaning roughly that
the next grammar rule to apply at any point in the input is uniquely
determined by the preceding input and a fixed, finite portion (called
a @dfn{look-ahead}) of the remaining input.
@@ -415,8 +422,9 @@ there are multiple ways to apply the grammar rules to get the some inputs.
Even unambiguous grammars can be @dfn{non-deterministic}, meaning that no
fixed look-ahead always suffices to determine the next grammar rule to apply.
With the proper declarations, Bison is also able to parse these more general
context-free grammars, using a technique known as GLR parsing (for
Generalized LR). Bison's GLR parsers are able to handle any context-free
context-free grammars, using a technique known as @acronym{GLR} parsing (for
Generalized @acronym{LR}). Bison's @acronym{GLR} parsers are able to
handle any context-free
grammar for which the number of possible parses of any given string
is finite.
@@ -518,7 +526,7 @@ for Bison, you must write a file expressing the grammar in Bison syntax:
a @dfn{Bison grammar} file. @xref{Grammar File, ,Bison Grammar Files}.
A nonterminal symbol in the formal grammar is represented in Bison input
as an identifier, like an identifier in C. By convention, it should be
as an identifier, like an identifier in C@. By convention, it should be
in lower case, such as @code{expr}, @code{stmt} or @code{declaration}.
The Bison representation for a terminal symbol is also called a @dfn{token
@@ -567,7 +575,8 @@ grammatical.
But the precise value is very important for what the input means once it is
parsed. A compiler is useless if it fails to distinguish between 4, 1 and
3989 as constants in the program! Therefore, each token in a Bison grammar
has both a token type and a @dfn{semantic value}. @xref{Semantics, ,Defining Language Semantics},
has both a token type and a @dfn{semantic value}. @xref{Semantics,
,Defining Language Semantics},
for details.
The token type is a terminal symbol defined in the grammar, such as
@@ -626,14 +635,14 @@ The action says how to produce the semantic value of the sum expression
from the values of the two subexpressions.
@node GLR Parsers
@section Writing GLR Parsers
@cindex GLR parsing
@cindex generalized LR (GLR) parsing
@section Writing @acronym{GLR} Parsers
@cindex @acronym{GLR} parsing
@cindex generalized @acronym{LR} (@acronym{GLR}) parsing
@findex %glr-parser
@cindex conflicts
@cindex shift/reduce conflicts
In some grammars, there will be cases where Bison's standard LALR(1)
In some grammars, there will be cases where Bison's standard @acronym{LALR}(1)
parsing algorithm cannot decide whether to apply a certain grammar rule
at a given point. That is, it may not be able to decide (on the basis
of the input read so far) which of two possible reductions (applications
@@ -642,14 +651,16 @@ of the input and apply a reduction later in the input. These are known
respectively as @dfn{reduce/reduce} conflicts (@pxref{Reduce/Reduce}),
and @dfn{shift/reduce} conflicts (@pxref{Shift/Reduce}).
To use a grammar that is not easily modified to be LALR(1), a more
To use a grammar that is not easily modified to be @acronym{LALR}(1), a more
general parsing algorithm is sometimes necessary. If you include
@code{%glr-parser} among the Bison declarations in your file
(@pxref{Grammar Outline}), the result will be a Generalized LR (GLR)
(@pxref{Grammar Outline}), the result will be a Generalized
@acronym{LR} (@acronym{GLR})
parser. These parsers handle Bison grammars that contain no unresolved
conflicts (i.e., after applying precedence declarations) identically to
LALR(1) parsers. However, when faced with unresolved shift/reduce and
reduce/reduce conflicts, GLR parsers use the simple expedient of doing
@acronym{LALR}(1) parsers. However, when faced with unresolved
shift/reduce and reduce/reduce conflicts, @acronym{GLR} parsers use
the simple expedient of doing
both, effectively cloning the parser to follow both possibilities. Each
of the resulting parsers can again split, so that at any given time,
there can be any number of possible parses being explored. The parsers
@@ -723,7 +734,8 @@ T (x) = y+z;
@noindent
parses as either an @code{expr} or a @code{stmt}
(assuming that @samp{T} is recognized as a TYPENAME and @samp{x} as an ID).
(assuming that @samp{T} is recognized as a @code{TYPENAME} and
@samp{x} as an @code{ID}).
Bison detects this as a reduce/reduce conflict between the rules
@code{expr : ID} and @code{declarator : ID}, which it cannot resolve at the
time it encounters @code{x} in the example above. The two @code{%dprec}
@@ -876,7 +888,7 @@ this manual.
In some cases the Bison parser file includes system headers, and in
those cases your code should respect the identifiers reserved by those
headers. On some non-@sc{gnu} hosts, @code{<alloca.h>},
headers. On some non-@acronym{GNU} hosts, @code{<alloca.h>},
@code{<stddef.h>}, and @code{<stdlib.h>} are included as needed to
declare memory allocators and related types. Other system headers may
be included if you define @code{YYDEBUG} to a nonzero value
@@ -1244,7 +1256,8 @@ or sequences of characters into tokens. The Bison parser gets its
tokens by calling the lexical analyzer. @xref{Lexical, ,The Lexical
Analyzer Function @code{yylex}}.
Only a simple lexical analyzer is needed for the RPN calculator. This
Only a simple lexical analyzer is needed for the @acronym{RPN}
calculator. This
lexical analyzer skips blanks and tabs, then reads in numbers as
@code{double} and returns them as @code{NUM} tokens. Any other character
that isn't part of a number is a separate token. Note that the token-code
@@ -1381,7 +1394,7 @@ bison @var{file_name}.y
@noindent
In this example the file was called @file{rpcalc.y} (for ``Reverse Polish
CALCulator''). Bison produces a file named @file{@var{file_name}.tab.c},
@sc{calc}ulator''). Bison produces a file named @file{@var{file_name}.tab.c},
removing the @samp{.y} from the original file name. The file output by
Bison contains the source code for @code{yyparse}. The additional
functions in the input file (@code{yylex}, @code{yyerror} and @code{main})
@@ -1451,7 +1464,7 @@ parentheses nested to arbitrary depth. Here is the Bison code for
#include <math.h>
%@}
/* BISON Declarations */
/* Bison Declarations */
%token NUM
%left '-' '+'
%left '*' '/'
@@ -2321,7 +2334,7 @@ There are three ways of writing terminal symbols in the grammar:
@itemize @bullet
@item
A @dfn{named token type} is written with an identifier, like an
identifier in C. By convention, it should be all upper case. Each
identifier in C@. By convention, it should be all upper case. Each
such name must be defined with a Bison declaration such as
@code{%token}. @xref{Token Decl, ,Token Type Names}.
@@ -2365,7 +2378,7 @@ Declarations}). If you don't do that, the lexical analyzer has to
retrieve the token number for the literal string token from the
@code{yytname} table (@pxref{Calling Convention}).
@strong{WARNING}: literal string tokens do not work in Yacc.
@strong{Warning}: literal string tokens do not work in Yacc.
By convention, a literal string token is used only to represent a token
that consists of that particular string. Thus, you should use the token
@@ -2404,7 +2417,7 @@ in the other source files that need it. @xref{Invocation, ,Invoking Bison}.
If you want to write a grammar that is portable to any Standard C
host, you must use only non-null character tokens taken from the basic
execution character set of Standard C. This set consists of the ten
execution character set of Standard C@. This set consists of the ten
digits, the 52 lower- and upper-case English letters, and the
characters in the following C-language string:
@@ -2414,14 +2427,14 @@ characters in the following C-language string:
The @code{yylex} function and Bison must use a consistent character
set and encoding for character tokens. For example, if you run Bison in an
@sc{ascii} environment, but then compile and run the resulting program
@acronym{ASCII} environment, but then compile and run the resulting program
in an environment that uses an incompatible character set like
@sc{ebcdic}, the resulting program may not work because the
tables generated by Bison will assume @sc{ascii} numeric values for
@acronym{EBCDIC}, the resulting program may not work because the
tables generated by Bison will assume @acronym{ASCII} numeric values for
character tokens. It is standard
practice for software distributions to contain C source files that
were generated by Bison in an @sc{ascii} environment, so installers on
platforms that are incompatible with @sc{ascii} must rebuild those
were generated by Bison in an @acronym{ASCII} environment, so installers on
platforms that are incompatible with @acronym{ASCII} must rebuild those
files before compiling them.
The symbol @code{error} is a terminal symbol reserved for error recovery
@@ -2627,7 +2640,7 @@ the numbers associated with @var{x} and @var{y}.
In a simple program it may be sufficient to use the same data type for
the semantic values of all language constructs. This was true in the
RPN and infix calculator examples (@pxref{RPN Calc, ,Reverse Polish
@acronym{RPN} and infix calculator examples (@pxref{RPN Calc, ,Reverse Polish
Notation Calculator}).
Bison's default is to use type @code{int} for all semantic values. To
@@ -2678,7 +2691,7 @@ is to compute a semantic value for the grouping built by the rule from the
semantic values associated with tokens or smaller groupings.
An action consists of C statements surrounded by braces, much like a
compound statement in C. It can be placed at any position in the rule;
compound statement in C@. It can be placed at any position in the rule;
it is executed at that position. Most rules have just one action at the
end of the rule, following all the components. Actions in the middle of
a rule are tricky and used only for special purposes (@pxref{Mid-Rule
@@ -3090,7 +3103,7 @@ the location of the grouping (the result of the computation). The second one
is an array holding locations of all right hand side elements of the rule
being matched. The last one is the size of the right hand side rule.
By default, it is defined this way for simple LALR(1) parsers:
By default, it is defined this way for simple @acronym{LALR}(1) parsers:
@example
@group
@@ -3103,7 +3116,7 @@ By default, it is defined this way for simple LALR(1) parsers:
@end example
@noindent
and like this for GLR parsers:
and like this for @acronym{GLR} parsers:
@example
@group
@@ -3419,8 +3432,8 @@ handler. In systems with multiple threads of control, a non-reentrant
program must be called only within interlocks.
Normally, Bison generates a parser which is not reentrant. This is
suitable for most uses, and it permits compatibility with YACC. (The
standard YACC interfaces are inherently nonreentrant, because they use
suitable for most uses, and it permits compatibility with Yacc. (The
standard Yacc interfaces are inherently nonreentrant, because they use
statically allocated variables for communication with @code{yylex},
including @code{yylval} and @code{yylloc}.)
@@ -4082,7 +4095,7 @@ Return immediately from @code{yyparse}, indicating success.
@findex YYBACKUP
Unshift a token. This macro is allowed only for rules that reduce
a single value, and only when there is no look-ahead token.
It is also disallowed in GLR parsers.
It is also disallowed in @acronym{GLR} parsers.
It installs a look-ahead token with token type @var{token} and
semantic value @var{value}; then it discards the value that was
going to be reduced by this rule.
@@ -4751,12 +4764,13 @@ name_list:
It would seem that this grammar can be parsed with only a single token
of look-ahead: when a @code{param_spec} is being read, an @code{ID} is
a @code{name} if a comma or colon follows, or a @code{type} if another
@code{ID} follows. In other words, this grammar is LR(1).
@code{ID} follows. In other words, this grammar is @acronym{LR}(1).
@cindex LR(1)
@cindex LALR(1)
@cindex @acronym{LR}(1)
@cindex @acronym{LALR}(1)
However, Bison, like most parser generators, cannot actually handle all
LR(1) grammars. In this grammar, two contexts, that after an @code{ID}
@acronym{LR}(1) grammars. In this grammar, two contexts, that after
an @code{ID}
at the beginning of a @code{param_spec} and likewise at the beginning of
a @code{return_spec}, are similar enough that Bison assumes they are the
same. They appear similar because the same set of rules would be
@@ -4765,11 +4779,12 @@ a @code{type}. Bison is unable to determine at that stage of processing
that the rules would require different look-ahead tokens in the two
contexts, so it makes a single parser state for them both. Combining
the two contexts causes a conflict later. In parser terminology, this
occurrence means that the grammar is not LALR(1).
occurrence means that the grammar is not @acronym{LALR}(1).
In general, it is better to fix deficiencies than to document them. But
this particular deficiency is intrinsically hard to fix; parser
generators that can handle LR(1) grammars are hard to write and tend to
generators that can handle @acronym{LR}(1) grammars are hard to write
and tend to
produce parsers that are very large. In practice, Bison is more useful
as it is now.
@@ -4819,9 +4834,9 @@ return_spec:
@end example
@node Generalized LR Parsing
@section Generalized LR (GLR) Parsing
@cindex GLR parsing
@cindex generalized LR (GLR) parsing
@section Generalized @acronym{LR} (@acronym{GLR}) Parsing
@cindex @acronym{GLR} parsing
@cindex generalized @acronym{LR} (@acronym{GLR}) parsing
@cindex ambiguous grammars
@cindex non-deterministic parsing
@@ -4841,16 +4856,18 @@ summarize the input seen so far loses necessary information.
When you use the @samp{%glr-parser} declaration in your grammar file,
Bison generates a parser that uses a different algorithm, called
Generalized LR (or GLR). A Bison GLR parser uses the same basic
Generalized @acronym{LR} (or @acronym{GLR}). A Bison @acronym{GLR}
parser uses the same basic
algorithm for parsing as an ordinary Bison parser, but behaves
differently in cases where there is a shift-reduce conflict that has not
been resolved by precedence rules (@pxref{Precedence}) or a
reduce-reduce conflict. When a GLR parser encounters such a situation, it
reduce-reduce conflict. When a @acronym{GLR} parser encounters such a
situation, it
effectively @emph{splits} into a several parsers, one for each possible
shift or reduction. These parsers then proceed as usual, consuming
tokens in lock-step. Some of the stacks may encounter other conflicts
and split further, with the result that instead of a sequence of states,
a Bison GLR parsing stack is what is in effect a tree of states.
a Bison @acronym{GLR} parsing stack is what is in effect a tree of states.
In effect, each stack represents a guess as to what the proper parse
is. Additional input may indicate that a guess was wrong, in which case
@@ -4866,7 +4883,7 @@ grammar symbol that produces the same segment of the input token
stream.
Whenever the parser makes a transition from having multiple
states to having one, it reverts to the normal LALR(1) parsing
states to having one, it reverts to the normal @acronym{LALR}(1) parsing
algorithm, after resolving and executing the saved-up actions.
At this transition, some of the states on the stack will have semantic
values that are sets (actually multisets) of possible actions. The
@@ -4878,9 +4895,10 @@ rules by the @samp{%merge} declaration,
Bison resolves and evaluates both and then calls the merge function on
the result. Otherwise, it reports an ambiguity.
It is possible to use a data structure for the GLR parsing tree that
permits the processing of any LALR(1) grammar in linear time (in the
size of the input), any unambiguous (not necessarily LALR(1)) grammar in
It is possible to use a data structure for the @acronym{GLR} parsing tree that
permits the processing of any @acronym{LALR}(1) grammar in linear time (in the
size of the input), any unambiguous (not necessarily
@acronym{LALR}(1)) grammar in
quadratic worst-case time, and any general (possibly ambiguous)
context-free grammar in cubic worst-case time. However, Bison currently
uses a simpler data structure that requires time proportional to the
@@ -4890,7 +4908,7 @@ grammars can require exponential time and space to process. Such badly
behaving examples, however, are not generally of practical interest.
Usually, non-determinism in a grammar is local---the parser is ``in
doubt'' only for a few tokens at a time. Therefore, the current data
structure should generally be adequate. On LALR(1) portions of a
structure should generally be adequate. On @acronym{LALR}(1) portions of a
grammar, in particular, it is only slightly slower than with the default
Bison parser.
@@ -4905,7 +4923,7 @@ not reduced. When this happens, the parser function @code{yyparse}
returns a nonzero value, pausing only to call @code{yyerror} to report
the overflow.
Becaue Bison parsers have growing stacks, hitting the upper limit
Because Bison parsers have growing stacks, hitting the upper limit
usually results from using a right recursion instead of a left
recursion, @xref{Recursion, ,Recursive Rules}.
@@ -4933,7 +4951,8 @@ macro @code{YYINITDEPTH}. This value too must be a compile-time
constant integer. The default is 200.
@c FIXME: C++ output.
Because of semantical differences between C and C++, the LALR(1) parsers
Because of semantical differences between C and C++, the
@acronym{LALR}(1) parsers
in C produced by Bison by compiled as C++ cannot grow. In this precise
case (compiling a C parser as C++) you are suggested to grow
@code{YYINITDEPTH}. In the near future, a C++ output output will be
@@ -5090,7 +5109,7 @@ This looks like a function call statement, but if @code{foo} is a typedef
name, then this is actually a declaration of @code{x}. How can a Bison
parser for C decide how to parse this input?
The method used in GNU C is to have two different token types,
The method used in @acronym{GNU} C is to have two different token types,
@code{IDENTIFIER} and @code{TYPENAME}. When @code{yylex} finds an
identifier, it looks up the current declaration of the identifier in order
to decide which token type to return: @code{TYPENAME} if the identifier is
@@ -5283,7 +5302,7 @@ As documented elsewhere (@pxref{Algorithm, ,The Bison Parser Algorithm})
Bison parsers are @dfn{shift/reduce automata}. In some cases (much more
frequent than one would hope), looking at this automaton is required to
tune or simply fix a parser. Bison provides two different
representation of it, either textually or graphically (as a @sc{vcg}
representation of it, either textually or graphically (as a @acronym{VCG}
file).
The textual file is generated when the options @option{--report} or
@@ -5582,7 +5601,7 @@ sentence @samp{NUM + NUM / NUM} can be parsed as @samp{NUM + (NUM /
NUM)}, which corresponds to shifting @samp{/}, or as @samp{(NUM + NUM) /
NUM}, which corresponds to reducing rule 1.
Because in LALR(1) parsing a single decision can be made, Bison
Because in @acronym{LALR}(1) parsing a single decision can be made, Bison
arbitrarily chose to disable the reduction, see @ref{Shift/Reduce, ,
Shift/Reduce Conflicts}. Discarded actions are reported in between
square brackets.
@@ -5687,21 +5706,22 @@ There are several means to enable compilation of trace facilities:
@item the macro @code{YYDEBUG}
@findex YYDEBUG
Define the macro @code{YYDEBUG} to a nonzero value when you compile the
parser. This is compliant with POSIX Yacc. You could use
parser. This is compliant with @acronym{POSIX} Yacc. You could use
@samp{-DYYDEBUG=1} as a compiler option or you could put @samp{#define
YYDEBUG 1} in the prologue of the grammar file (@pxref{Prologue, , The
Prologue}).
@item the option @option{-t}, @option{--debug}
Use the @samp{-t} option when you run Bison (@pxref{Invocation,
,Invoking Bison}). This is POSIX compliant too.
,Invoking Bison}). This is @acronym{POSIX} compliant too.
@item the directive @samp{%debug}
@findex %debug
Add the @code{%debug} directive (@pxref{Decl Summary, ,Bison
Declaration Summary}). This is a Bison extension, which will prove
useful when Bison will output parsers for languages that don't use a
preprocessor. Useless POSIX and Yacc portability matter to you, this is
preprocessor. Unless @acronym{POSIX} and Yacc portability matter to
you, this is
the preferred solution.
@end table
@@ -5819,9 +5839,9 @@ will produce @file{output.c++} and @file{outfile.h++}.
@menu
* Bison Options:: All the options described in detail,
in alphabetical order by short options.
in alphabetical order by short options.
* Option Cross Key:: Alphabetical list of long options.
* VMS Invocation:: Bison command syntax on VMS.
* VMS Invocation:: Bison command syntax on @acronym{VMS}.
@end menu
@node Bison Options
@@ -5931,7 +5951,7 @@ separated list of @var{things} among:
@table @code
@item state
Description of the grammar, conflicts (resolved and unresolved), and
LALR automaton.
@acronym{LALR} automaton.
@item lookahead
Implies @code{state} and augments the description of the automaton with
@@ -5958,8 +5978,9 @@ The other output files' names are constructed from @var{filename} as
described under the @samp{-v} and @samp{-d} options.
@item -g
Output a VCG definition of the LALR(1) grammar automaton computed by
Bison. If the grammar file is @file{foo.y}, the VCG output file will
Output a @acronym{VCG} definition of the @acronym{LALR}(1) grammar
automaton computed by Bison. If the grammar file is @file{foo.y}, the
@acronym{VCG} output file will
be @file{foo.vcg}.
@item --graph=@var{graph-file}
@@ -6013,30 +6034,30 @@ the corresponding short option.
@end ifinfo
@node VMS Invocation
@section Invoking Bison under VMS
@cindex invoking Bison under VMS
@cindex VMS
@section Invoking Bison under @acronym{VMS}
@cindex invoking Bison under @acronym{VMS}
@cindex @acronym{VMS}
The command line syntax for Bison on VMS is a variant of the usual
Bison command syntax---adapted to fit VMS conventions.
The command line syntax for Bison on @acronym{VMS} is a variant of the usual
Bison command syntax---adapted to fit @acronym{VMS} conventions.
To find the VMS equivalent for any Bison option, start with the long
To find the @acronym{VMS} equivalent for any Bison option, start with the long
option, and substitute a @samp{/} for the leading @samp{--}, and
substitute a @samp{_} for each @samp{-} in the name of the long option.
For example, the following invocation under VMS:
For example, the following invocation under @acronym{VMS}:
@example
bison /debug/name_prefix=bar foo.y
@end example
@noindent
is equivalent to the following command under POSIX.
is equivalent to the following command under @acronym{POSIX}.
@example
bison --debug --name-prefix=bar foo.y
@end example
The VMS file system does not permit filenames such as
The @acronym{VMS} file system does not permit filenames such as
@file{foo.tab.c}. In the above example, the output file
would instead be named @file{foo_tab.c}.
@@ -6243,14 +6264,16 @@ Bison declaration to create a header file meant for the scanner.
@item %dprec
Bison declaration to assign a precedence to a rule that is used at parse
time to resolve reduce/reduce conflicts. @xref{GLR Parsers}.
time to resolve reduce/reduce conflicts. @xref{GLR Parsers, ,Writing
@acronym{GLR} Parsers}.
@item %file-prefix="@var{prefix}"
Bison declaration to set the prefix of the output files. @xref{Decl
Summary}.
@item %glr-parser
Bison declaration to produce a GLR parser. @xref{GLR Parsers}.
Bison declaration to produce a @acronym{GLR} parser. @xref{GLR
Parsers, ,Writing @acronym{GLR} Parsers}.
@c @item %source-extension
@c Bison declaration to specify the generated parser output file extension.
@@ -6268,7 +6291,7 @@ Bison declaration to assign left associativity to token(s).
Bison declaration to assign a merging function to a rule. If there is a
reduce/reduce conflict with a rule having the same merging function, the
function is applied to the two semantic values to get a single result.
@xref{GLR Parsers}.
@xref{GLR Parsers, ,Writing @acronym{GLR} Parsers}.
@item %name-prefix="@var{prefix}"
Bison declaration to rename the external symbols. @xref{Decl Summary}.
@@ -6354,10 +6377,11 @@ Separates alternate rules for the same result nonterminal.
@cindex glossary
@table @asis
@item Backus-Naur Form (BNF)
Formal method of specifying context-free grammars. BNF was first used
in the @cite{ALGOL-60} report, 1963. @xref{Language and Grammar,
,Languages and Context-Free Grammars}.
@item Backus-Naur Form (@acronym{BNF}; also called ``Backus Normal Form'')
Formal method of specifying context-free grammars originally proposed
by John Backus, and slightly improved by Peter Naur in his 1960-01-02
committee document contributing to what became the Algol 60 report.
@xref{Language and Grammar, ,Languages and Context-Free Grammars}.
@item Context-free grammars
Grammars specified as rules that can be applied regardless of context.
@@ -6380,18 +6404,20 @@ each instant in time. As input to the machine is processed, the
machine moves from state to state as specified by the logic of the
machine. In the case of the parser, the input is the language being
parsed, and the states correspond to various stages in the grammar
rules. @xref{Algorithm, ,The Bison Parser Algorithm }.
rules. @xref{Algorithm, ,The Bison Parser Algorithm}.
@item Generalized LR (GLR)
@item Generalized @acronym{LR} (@acronym{GLR})
A parsing algorithm that can handle all context-free grammars, including those
that are not LALR(1). It resolves situations that Bison's usual LALR(1)
that are not @acronym{LALR}(1). It resolves situations that Bison's
usual @acronym{LALR}(1)
algorithm cannot by effectively splitting off multiple parsers, trying all
possible parsers, and discarding those that fail in the light of additional
right context. @xref{Generalized LR Parsing, ,Generalized LR Parsing}.
right context. @xref{Generalized LR Parsing, ,Generalized
@acronym{LR} Parsing}.
@item Grouping
A language construct that is (in general) grammatically divisible;
for example, `expression' or `declaration' in C.
for example, `expression' or `declaration' in C@.
@xref{Language and Grammar, ,Languages and Context-Free Grammars}.
@item Infix operator
@@ -6418,7 +6444,7 @@ Rules}.
@item Left-to-right parsing
Parsing a sentence of a language by analyzing it token by token from
left to right. @xref{Algorithm, ,The Bison Parser Algorithm }.
left to right. @xref{Algorithm, ,The Bison Parser Algorithm}.
@item Lexical analyzer (scanner)
A function that reads an input stream and returns tokens one by one.
@@ -6435,12 +6461,12 @@ A token which consists of two or more fixed characters. @xref{Symbols}.
A token already read but not yet shifted. @xref{Look-Ahead, ,Look-Ahead
Tokens}.
@item LALR(1)
@item @acronym{LALR}(1)
The class of context-free grammars that Bison (like most other parser
generators) can handle; a subset of LR(1). @xref{Mystery Conflicts, ,
Mysterious Reduce/Reduce Conflicts}.
generators) can handle; a subset of @acronym{LR}(1). @xref{Mystery
Conflicts, ,Mysterious Reduce/Reduce Conflicts}.
@item LR(1)
@item @acronym{LR}(1)
The class of context-free grammars in which at most one token of
look-ahead is needed to disambiguate the parsing of any piece of input.
@@ -6465,7 +6491,7 @@ performs some operation.
@item Reduction
Replacing a string of nonterminals and/or terminals with a single
nonterminal, according to a grammar rule. @xref{Algorithm, ,The Bison
Parser Algorithm }.
Parser Algorithm}.
@item Reentrant
A reentrant subprogram is a subprogram which can be in invoked any
@@ -6488,7 +6514,7 @@ each statement. @xref{Semantics, ,Defining Language Semantics}.
@item Shift
A parser is said to shift when it makes the choice of analyzing
further input from the stream rather than reducing immediately some
already-recognized rule. @xref{Algorithm, ,The Bison Parser Algorithm }.
already-recognized rule. @xref{Algorithm, ,The Bison Parser Algorithm}.
@item Single-character literal
A single character that is recognized and interpreted as is.