Writing @acronym{GLR} Parsers
-* Simple GLR Parsers:: Using @acronym{GLR} parsers on unambiguous grammars
-* Merging GLR Parses:: Using @acronym{GLR} parsers to resolve ambiguities
-* Compiler Requirements:: @acronym{GLR} parsers require a modern C compiler
+* Simple GLR Parsers:: Using @acronym{GLR} parsers on unambiguous grammars
+* Merging GLR Parses:: Using @acronym{GLR} parsers to resolve ambiguities
+* Compiler Requirements:: @acronym{GLR} parsers require a modern C compiler
Examples
Bison Declarations
+* Require Decl:: Requiring a Bison version.
* Token Decl:: Declaring terminal symbols.
* Precedence Decl:: Declaring terminals with precedence and associativity.
* Union Decl:: Declaring the set of all semantic value types.
merged result.
@menu
-* Simple GLR Parsers:: Using @acronym{GLR} parsers on unambiguous grammars
-* Merging GLR Parses:: Using @acronym{GLR} parsers to resolve ambiguities
-* Compiler Requirements:: @acronym{GLR} parsers require a modern C compiler
+* Simple GLR Parsers:: Using @acronym{GLR} parsers on unambiguous grammars
+* Merging GLR Parses:: Using @acronym{GLR} parsers to resolve ambiguities
+* Compiler Requirements:: @acronym{GLR} parsers require a modern C compiler
@end menu
@node Simple GLR Parsers
Grammars}).
@menu
+* Require Decl:: Requiring a Bison version.
* Token Decl:: Declaring terminal symbols.
* Precedence Decl:: Declaring terminals with precedence and associativity.
* Union Decl:: Declaring the set of all semantic value types.
* Decl Summary:: Table of all Bison declarations.
@end menu
+@node Require Decl
+@subsection Require a Version of Bison
+@cindex version requirement
+@cindex requiring a version of Bison
+@findex %require
+
+You may require the minimum version of Bison to process the grammar. If
+the requirement is not met, @command{bison} exits with an error (exit
+status 63).
+
+@example
+%require "@var{version}"
+@end example
+
@node Token Decl
@subsection Token Type Names
@cindex declaring token type names
%parse-param @{ char const *file_name @};
%initial-action
@{
- @@$.begin.filename = @@$.end.filename = file_name;
+ @@$.initialize (file_name);
@};
@end example
@cindex freeing discarded symbols
@findex %destructor
-Some symbols can be discarded by the parser. During error
-recovery (@pxref{Error Recovery}), symbols already pushed
-on the stack and tokens coming from the rest of the file
-are discarded until the parser falls on its feet. If the parser
-runs out of memory, all the symbols on the stack must be discarded.
-Even if the parser succeeds, it must discard the start symbol.
+Some symbols can be discarded by the parser. During error recovery
+(@pxref{Error Recovery}), symbols already pushed on the stack and tokens
+coming from the rest of the file are discarded until the parser falls on
+its feet. If the parser runs out of memory, all the symbols on the
+stack must be discarded. Even if the parser succeeds, it must discard
+the start symbol.
When discarded symbols convey heap based information, this memory is
lost. While this behavior can be tolerable for batch parsers, such as
-in traditional compilers, it is unacceptable for programs like shells
-or protocol implementations that may parse and execute indefinitely.
+in traditional compilers, it is unacceptable for programs like shells or
+protocol implementations that may parse and execute indefinitely.
The @code{%destructor} directive defines code that
is called when a symbol is discarded.
@deffn {Directive} %destructor @{ @var{code} @} @var{symbols}
@findex %destructor
-Invoke @var{code} whenever the parser discards one of the
-@var{symbols}. Within @var{code}, @code{$$} designates the semantic
-value associated with the discarded symbol. The additional
-parser parameters are also available
-(@pxref{Parser Function, , The Parser Function @code{yyparse}}).
+Invoke @var{code} whenever the parser discards one of the @var{symbols}.
+Within @var{code}, @code{$$} designates the semantic value associated
+with the discarded symbol. The additional parser parameters are also
+available (@pxref{Parser Function, , The Parser Function
+@code{yyparse}}).
@strong{Warning:} as of Bison 2.1, this feature is still
experimental, as there has not been enough user feedback. In particular,
(Reentrant) Parser}).
@end deffn
+@deffn {Directive} %require "@var{version}"
+Require version @var{version} or higher of Bison. @xref{Require Decl, ,
+Require a Version of Bison}.
+@end deffn
+
@deffn {Directive} %token-table
Generate an array of token names in the parser file. The name of the
array is @code{yytname}; @code{yytname[@var{i}]} is the name of the
The @code{%union} directive works as for C, see @ref{Union Decl, ,The
Collection of Value Types}. In particular it produces a genuine
@code{union}@footnote{In the future techniques to allow complex types
-within pseudo-unions (variants) might be implemented to alleviate
-these issues.}, which have a few specific features in C++.
+within pseudo-unions (similar to Boost variants) might be implemented to
+alleviate these issues.}, which have a few specific features in C++.
@itemize @minus
@item
-The name @code{YYSTYPE} also denotes @samp{union YYSTYPE}. You may
-forward declare it just with @samp{union YYSTYPE;}.
+The type @code{YYSTYPE} is defined but its use is discouraged: rather
+you should refer to the parser's encapsulated type
+@code{yy::parser::semantic_type}.
@item
Non POD (Plain Old Data) types cannot be used. C++ forbids any
instance of classes with constructors in unions: only @emph{pointers}
The declaration of this driver class, @file{calc++-driver.hh}, is as
follows. The first part includes the CPP guard and imports the
-required standard library components.
+required standard library components, and the declaration of the parser
+class.
@comment file: calc++-driver.hh
@example
# define CALCXX_DRIVER_HH
# include <string>
# include <map>
+# include "calc++-parser.hh"
@end example
-@noindent
-Then come forward declarations. Because the parser uses the parsing
-driver and reciprocally, simple inclusions of header files will not
-do. Because the driver's declaration is the one that will be imported
-by the rest of the project, it is saner to forward declare the
-parser's information here.
-
-@comment file: calc++-driver.hh
-@example
-// Forward declarations.
-union YYSTYPE;
-namespace yy
-@{
- class location;
- class calcxx_parser;
-@}
-class calcxx_driver;
-@end example
@noindent
Then comes the declaration of the scanning function. Flex expects
@example
// Announce to Flex the prototype we want for lexing function, ...
# define YY_DECL \
- int yylex (YYSTYPE* yylval, yy::location* yylloc, calcxx_driver& driver)
+ int yylex (yy::calcxx_parser::semantic_type* yylval, \
+ yy::calcxx_parser::location_type* yylloc, \
+ calcxx_driver& driver)
// ... and declare it for the parser's sake.
YY_DECL;
@end example
@node Calc++ Parser
@subsection Calc++ Parser
-The parser definition file @file{calc++-parser.yy} starts by asking
-for the C++ skeleton, the creation of the parser header file, and
-specifies the name of the parser class. It then includes the required
-headers.
+The parser definition file @file{calc++-parser.yy} starts by asking for
+the C++ LALR(1) skeleton, the creation of the parser header file, and
+specifies the name of the parser class. Because the C++ skeleton
+changed several times, it is safer to require the version you designed
+the grammar for.
@comment file: calc++-parser.yy
@example
%skeleton "lalr1.cc" /* -*- C++ -*- */
-%define "parser_class_name" "calcxx_parser"
+%require "2.1a"
%defines
+%define "parser_class_name" "calcxx_parser"
+@end example
+
+@noindent
+Then come the declarations/inclusions needed to define the
+@code{%union}. Because the parser uses the parsing driver and
+reciprocally, both cannot include the header of the other. Because the
+driver's header needs detailed knowledge about the parser class (in
+particular its inner types), it is the parser's header which will simply
+use a forward declaration of the driver.
+
+@comment file: calc++-parser.yy
+@example
%@{
# include <string>
-# include "calc++-driver.hh"
+class calcxx_driver;
%@}
@end example
@};
@end example
+@noindent
+The code between @samp{%@{} and @samp{%@}} after the introduction of the
+@samp{%union} is output in the @file{*.cc} file; it needs detailed
+knowledge about the driver.
+
+@comment file: calc++-parser.yy
+@example
+%@{
+# include "calc++-driver.hh"
+%@}
+@end example
+
+
@noindent
The token numbered as 0 corresponds to end of file; the following line
allows for nicer error messages referring to ``end of file'' instead
@comment file: calc++-parser.yy
@example
-%token TOKEN_EOF 0 "end of file"
-%token TOKEN_ASSIGN ":="
-%token <sval> TOKEN_IDENTIFIER "identifier"
-%token <ival> TOKEN_NUMBER "number"
-%type <ival> exp "expression"
+%token END 0 "end of file"
+%token ASSIGN ":="
+%token <sval> IDENTIFIER "identifier"
+%token <ival> NUMBER "number"
+%type <ival> exp "expression"
@end example
@noindent
assignments: assignments assignment @{@}
| /* Nothing. */ @{@};
-assignment: TOKEN_IDENTIFIER ":=" exp @{ driver.variables[*$1] = $3; @};
+assignment: "identifier" ":=" exp @{ driver.variables[*$1] = $3; @};
%left '+' '-';
%left '*' '/';
| exp '-' exp @{ $$ = $1 - $3; @}
| exp '*' exp @{ $$ = $1 * $3; @}
| exp '/' exp @{ $$ = $1 / $3; @}
- | TOKEN_IDENTIFIER @{ $$ = driver.variables[*$1]; @}
- | TOKEN_NUMBER @{ $$ = $1; @};
+ | "identifier" @{ $$ = driver.variables[*$1]; @}
+ | "number" @{ $$ = $1; @};
%%
@end example
@end example
@noindent
-The rules are simple, just note the use of the driver to report
-errors.
+The rules are simple, just note the use of the driver to report errors.
+It is convenient to use a typedef to shorten
+@code{yy::calcxx_parser::token::identifier} into
+@code{token::identifier} for isntance.
@comment file: calc++-scanner.ll
@example
+%@{
+ typedef yy::calcxx_parser::token token;
+%@}
+
[-+*/] return yytext[0];
-":=" return TOKEN_ASSIGN;
+":=" return token::ASSIGN;
@{int@} @{
errno = 0;
long n = strtol (yytext, NULL, 10);
if (! (INT_MIN <= n && n <= INT_MAX && errno != ERANGE))
driver.error (*yylloc, "integer is out of range");
yylval->ival = n;
- return TOKEN_NUMBER;
+ return token::NUMBER;
@}
-@{id@} yylval->sval = new std::string (yytext); return TOKEN_IDENTIFIER;
+@{id@} yylval->sval = new std::string (yytext); return token::IDENTIFIER;
. driver.error (*yylloc, "invalid character");
%%
@end example
@xref{Pure Decl, ,A Pure (Reentrant) Parser}.
@end deffn
+@deffn {Directive} %require "@var{version}"
+Require version @var{version} or higher of Bison. @xref{Require Decl, ,
+Require a Version of Bison}.
+@end deffn
+
@deffn {Directive} %right
Bison declaration to assign right associativity to token(s).
@xref{Precedence Decl, ,Operator Precedence}.
projects / bison.git / blobdiff