maint: avoid "magic number exit".

[bison.git] / doc / bison.texinfo

diff --git a/doc/bison.texinfo b/doc/bison.texinfo
index 8fdac074ae066d11ce0fe3833d178dcd631b3e90..329d81d0d864c16dfe1c211bb684db44c86e445c 100644 (file)
--- a/doc/bison.texinfo
+++ b/doc/bison.texinfo
@@ -33,7 +33,7 @@
 This manual (@value{UPDATED}) is for GNU Bison (version
 @value{VERSION}), the GNU parser generator.
 
 This manual (@value{UPDATED}) is for GNU Bison (version
 @value{VERSION}), the GNU parser generator.
 

-Copyright @copyright{} 1988-1993, 1995, 1998-2011 Free Software
+Copyright @copyright{} 1988-1993, 1995, 1998-2012 Free Software

 Foundation, Inc.
 
 @quotation
 Foundation, Inc.
 
 @quotation


@@ -125,7 +125,7 @@ The Concepts of Bison
                            the name of an identifier, etc.).
 * Semantic Actions::     Each rule can have an action containing C code.
 * GLR Parsers::          Writing parsers for general context-free languages.
                            the name of an identifier, etc.).
 * Semantic Actions::     Each rule can have an action containing C code.
 * GLR Parsers::          Writing parsers for general context-free languages.

-* Locations Overview::   Tracking Locations.
+* Locations::            Overview of location tracking.

 * Bison Parser::         What are Bison's input and output,
                            how is the output used?
 * Stages::               Stages in writing and running Bison grammars.
 * Bison Parser::         What are Bison's input and output,
                            how is the output used?
 * Stages::               Stages in writing and running Bison grammars.


@@ -180,15 +180,15 @@ Multi-Function Calculator: @code{mfcalc}
 
 Bison Grammar Files
 
 
 Bison Grammar Files
 

-* Grammar Outline::   Overall layout of the grammar file.
-* Symbols::           Terminal and nonterminal symbols.
-* Rules::             How to write grammar rules.
-* Recursion::         Writing recursive rules.
-* Semantics::         Semantic values and actions.
-* Locations::         Locations and actions.
-* Named References::  Using named references in actions.
-* Declarations::      All kinds of Bison declarations are described here.
-* Multiple Parsers::  Putting more than one Bison parser in one program.
+* Grammar Outline::    Overall layout of the grammar file.
+* Symbols::            Terminal and nonterminal symbols.
+* Rules::              How to write grammar rules.
+* Recursion::          Writing recursive rules.
+* Semantics::          Semantic values and actions.
+* Tracking Locations:: Locations and actions.
+* Named References::   Using named references in actions.
+* Declarations::       All kinds of Bison declarations are described here.
+* Multiple Parsers::   Putting more than one Bison parser in one program.

 
 Outline of a Bison Grammar
 
 
 Outline of a Bison Grammar
 


@@ -449,7 +449,7 @@ use Bison or Yacc, we suggest you start by reading this chapter carefully.
                            the name of an identifier, etc.).
 * Semantic Actions::     Each rule can have an action containing C code.
 * GLR Parsers::          Writing parsers for general context-free languages.
                            the name of an identifier, etc.).
 * Semantic Actions::     Each rule can have an action containing C code.
 * GLR Parsers::          Writing parsers for general context-free languages.

-* Locations Overview::   Tracking Locations.
+* Locations::            Overview of location tracking.

 * Bison Parser::         What are Bison's input and output,
                            how is the output used?
 * Stages::               Stages in writing and running Bison grammars.
 * Bison Parser::         What are Bison's input and output,
                            how is the output used?
 * Stages::               Stages in writing and running Bison grammars.


@@ -1205,7 +1205,7 @@ will suffice.  Otherwise, we suggest
 %@}
 @end example
 
 %@}
 @end example
 

-@node Locations Overview
+@node Locations

 @section Locations
 @cindex location
 @cindex textual location
 @section Locations
 @cindex location
 @cindex textual location


@@ -1217,9 +1217,10 @@ the @dfn{textual location}, or @dfn{location}, of each syntactic construct.
 Bison provides a mechanism for handling these locations.
 
 Each token has a semantic value.  In a similar fashion, each token has an
 Bison provides a mechanism for handling these locations.
 
 Each token has a semantic value.  In a similar fashion, each token has an

-associated location, but the type of locations is the same for all tokens and
-groupings.  Moreover, the output parser is equipped with a default data
-structure for storing locations (@pxref{Locations}, for more details).
+associated location, but the type of locations is the same for all tokens
+and groupings.  Moreover, the output parser is equipped with a default data
+structure for storing locations (@pxref{Tracking Locations}, for more
+details).

 
 Like semantic values, locations can be reached in actions using a dedicated
 set of constructs.  In the example above, the location of the whole grouping
 
 Like semantic values, locations can be reached in actions using a dedicated
 set of constructs.  In the example above, the location of the whole grouping


@@ -2621,15 +2622,15 @@ The Bison grammar file conventionally has a name ending in @samp{.y}.
 @xref{Invocation, ,Invoking Bison}.
 
 @menu
 @xref{Invocation, ,Invoking Bison}.
 
 @menu

-* Grammar Outline::   Overall layout of the grammar file.
-* Symbols::           Terminal and nonterminal symbols.
-* Rules::             How to write grammar rules.
-* Recursion::         Writing recursive rules.
-* Semantics::         Semantic values and actions.
-* Locations::         Locations and actions.
-* Named References::  Using named references in actions.
-* Declarations::      All kinds of Bison declarations are described here.
-* Multiple Parsers::  Putting more than one Bison parser in one program.
+* Grammar Outline::    Overall layout of the grammar file.
+* Symbols::            Terminal and nonterminal symbols.
+* Rules::              How to write grammar rules.
+* Recursion::          Writing recursive rules.
+* Semantics::          Semantic values and actions.
+* Tracking Locations:: Locations and actions.
+* Named References::   Using named references in actions.
+* Declarations::       All kinds of Bison declarations are described here.
+* Multiple Parsers::   Putting more than one Bison parser in one program.

 @end menu
 
 @node Grammar Outline
 @end menu
 
 @node Grammar Outline


@@ -3509,8 +3510,8 @@ the addition-expression just recognized by the rule.  If there were a
 useful semantic value associated with the @samp{+} token, it could be
 referred to as @code{$2}.
 
 useful semantic value associated with the @samp{+} token, it could be
 referred to as @code{$2}.
 

-@xref{Named References,,Using Named References}, for more information
-about using the named references construct.
+@xref{Named References}, for more information about using the named
+references construct.

 
 Note that the vertical-bar character @samp{|} is really a rule
 separator, and actions are attached to a single rule.  This is a
 
 Note that the vertical-bar character @samp{|} is really a rule
 separator, and actions are attached to a single rule.  This is a


@@ -3806,7 +3807,7 @@ compound: subroutine
 Now Bison can execute the action in the rule for @code{subroutine} without
 deciding which rule for @code{compound} it will eventually use.
 
 Now Bison can execute the action in the rule for @code{subroutine} without
 deciding which rule for @code{compound} it will eventually use.
 

-@node Locations
+@node Tracking Locations

 @section Tracking Locations
 @cindex location
 @cindex textual location
 @section Tracking Locations
 @cindex location
 @cindex textual location


@@ -3876,8 +3877,8 @@ The location of the @var{n}th component of the right hand side is
 
 In addition, the named references construct @code{@@@var{name}} and
 @code{@@[@var{name}]} may also be used to address the symbol locations.
 
 In addition, the named references construct @code{@@@var{name}} and
 @code{@@[@var{name}]} may also be used to address the symbol locations.

-@xref{Named References,,Using Named References}, for more information
-about using the named references construct.
+@xref{Named References}, for more information about using the named
+references construct.

 
 Here is a basic example using the default data type for locations:
 
 
 Here is a basic example using the default data type for locations:
 


@@ -4015,13 +4016,19 @@ statement when it is followed by a semicolon.
 @end itemize
 
 @node Named References
 @end itemize
 
 @node Named References

-@section Using Named References
+@section Named References

 @cindex named references
 
 @cindex named references
 

-While every semantic value can be accessed with positional references
-@code{$@var{n}} and @code{$$}, it's often much more convenient to refer to
-them by name.  First of all, original symbol names may be used as named
-references.  For example:
+As described in the preceding sections, the traditional way to refer to any
+semantic value or location is a @dfn{positional reference}, which takes the
+form @code{$@var{n}}, @code{$$}, @code{@@@var{n}}, and @code{@@$}.  However,
+such a reference is not very descriptive.  Moreover, if you later decide to
+insert or remove symbols in the right-hand side of a grammar rule, the need
+to renumber such references can be tedious and error-prone.
+
+To avoid these issues, you can also refer to a semantic value or location
+using a @dfn{named reference}.  First of all, original symbol names may be
+used as named references.  For example:

 
 @example
 @group
 
 @example
 @group


@@ -4031,8 +4038,7 @@ invocation: op '(' args ')'
 @end example
 
 @noindent
 @end example
 
 @noindent

-The positional @code{$$}, @code{@@$}, @code{$n}, and @code{@@n} can be
-mixed with @code{$name} and @code{@@name} arbitrarily.  For example:
+Positional and named references can be mixed arbitrarily.  For example:

 
 @example
 @group
 
 @example
 @group


@@ -4070,10 +4076,9 @@ exp[result]: exp[left] '/' exp[right]
 @end example
 
 @noindent
 @end example
 
 @noindent

-Explicit names may be declared for RHS and for LHS symbols as well.  In order
-to access a semantic value generated by a mid-rule action, an explicit name
-may also be declared by putting a bracketed name after the closing brace of
-the mid-rule action code:
+In order to access a semantic value generated by a mid-rule action, an
+explicit name may also be declared by putting a bracketed name after the
+closing brace of the mid-rule action code:

 @example
 @group
 exp[res]: exp[x] '+' @{$left = $x;@}[left] exp[right]
 @example
 @group
 exp[res]: exp[x] '+' @{$left = $x;@}[left] exp[right]


@@ -4094,11 +4099,14 @@ if-stmt: IF '(' expr ')' THEN then.stmt ';'
 
 It often happens that named references are followed by a dot, dash or other
 C punctuation marks and operators.  By default, Bison will read
 
 It often happens that named references are followed by a dot, dash or other
 C punctuation marks and operators.  By default, Bison will read

-@code{$name.suffix} as a reference to symbol value @code{$name} followed by
-@samp{.suffix}, i.e., an access to the @samp{suffix} field of the semantic
-value.  In order to force Bison to recognize @code{name.suffix} in its entirety
-as the name of a semantic value, bracketed syntax @code{$[name.suffix]}
-must be used.
+@samp{$name.suffix} as a reference to symbol value @code{$name} followed by
+@samp{.suffix}, i.e., an access to the @code{suffix} field of the semantic
+value.  In order to force Bison to recognize @samp{name.suffix} in its
+entirety as the name of a semantic value, the bracketed syntax
+@samp{$[name.suffix]} must be used.
+
+The named references feature is experimental.  More user feedback will help
+to stabilize it.

 
 @node Declarations
 @section Bison Declarations
 
 @node Declarations
 @section Bison Declarations


@@ -4540,12 +4548,12 @@ redefine it from @code{$end} to, for example, @code{END}:
 @cindex mid-rule actions
 Finally, Bison will never invoke a @code{%destructor} for an unreferenced
 mid-rule semantic value (@pxref{Mid-Rule Actions,,Actions in Mid-Rule}).
 @cindex mid-rule actions
 Finally, Bison will never invoke a @code{%destructor} for an unreferenced
 mid-rule semantic value (@pxref{Mid-Rule Actions,,Actions in Mid-Rule}).

-That is, Bison does not consider a mid-rule to have a semantic value if you do
-not reference @code{$$} in the mid-rule's action or @code{$@var{n}} (where
-@var{n} is the RHS symbol position of the mid-rule) in any later action in that
-rule.
-However, if you do reference either, the Bison-generated parser will invoke the
-@code{<>} @code{%destructor} whenever it discards the mid-rule symbol.
+That is, Bison does not consider a mid-rule to have a semantic value if you
+do not reference @code{$$} in the mid-rule's action or @code{$@var{n}}
+(where @var{n} is the right-hand side symbol position of the mid-rule) in
+any later action in that rule.  However, if you do reference either, the
+Bison-generated parser will invoke the @code{<>} @code{%destructor} whenever
+it discards the mid-rule symbol.

 
 @ignore
 @noindent
 
 @ignore
 @noindent


@@ -4911,9 +4919,8 @@ Unless your parser is pure, the parser header file declares
 (Reentrant) Parser}.
 
 If you have also used locations, the parser header file declares
 (Reentrant) Parser}.
 
 If you have also used locations, the parser header file declares

-@code{YYLTYPE} and @code{yylloc} using a protocol similar to that of
-the @code{YYSTYPE} macro and @code{yylval}.  @xref{Locations,
-,Tracking Locations}.
+@code{YYLTYPE} and @code{yylloc} using a protocol similar to that of the
+@code{YYSTYPE} macro and @code{yylval}.  @xref{Tracking Locations}.

 
 This parser header file is normally essential if you wish to put the
 definition of @code{yylex} in a separate source file, because
 
 This parser header file is normally essential if you wish to put the
 definition of @code{yylex} in a separate source file, because


@@ -5752,12 +5759,12 @@ then the code in @code{yylex} might look like this:
 @subsection Textual Locations of Tokens
 
 @vindex yylloc
 @subsection Textual Locations of Tokens
 
 @vindex yylloc

-If you are using the @samp{@@@var{n}}-feature (@pxref{Locations, ,
-Tracking Locations}) in actions to keep track of the textual locations
-of tokens and groupings, then you must provide this information in
-@code{yylex}.  The function @code{yyparse} expects to find the textual
-location of a token just parsed in the global variable @code{yylloc}.
-So @code{yylex} must store the proper data in that variable.
+If you are using the @samp{@@@var{n}}-feature (@pxref{Tracking Locations})
+in actions to keep track of the textual locations of tokens and groupings,
+then you must provide this information in @code{yylex}.  The function
+@code{yyparse} expects to find the textual location of a token just parsed
+in the global variable @code{yylloc}.  So @code{yylex} must store the proper
+data in that variable.

 
 By default, the value of @code{yylloc} is a structure and you need only
 initialize the members that are going to be used by the actions.  The
 
 By default, the value of @code{yylloc} is a structure and you need only
 initialize the members that are going to be used by the actions.  The


@@ -6083,9 +6090,9 @@ Actions}).
 
 @deffn {Value} @@$
 @findex @@$
 
 @deffn {Value} @@$
 @findex @@$

-Acts like a structure variable containing information on the textual location
-of the grouping made by the current rule.  @xref{Locations, ,
-Tracking Locations}.
+Acts like a structure variable containing information on the textual
+location of the grouping made by the current rule.  @xref{Tracking
+Locations}.

 
 @c Check if those paragraphs are still useful or not.
 
 
 @c Check if those paragraphs are still useful or not.
 


@@ -6109,9 +6116,9 @@ Tracking Locations}.
 
 @deffn {Value} @@@var{n}
 @findex @@@var{n}
 
 @deffn {Value} @@@var{n}
 @findex @@@var{n}

-Acts like a structure variable containing information on the textual location
-of the @var{n}th component of the current rule.  @xref{Locations, ,
-Tracking Locations}.
+Acts like a structure variable containing information on the textual
+location of the @var{n}th component of the current rule.  @xref{Tracking
+Locations}.

 @end deffn
 
 @node Internationalization
 @end deffn
 
 @node Internationalization


@@ -8753,10 +8760,10 @@ Symbols}.
 @c - %define filename_type "const symbol::Symbol"
 
 When the directive @code{%locations} is used, the C++ parser supports
 @c - %define filename_type "const symbol::Symbol"
 
 When the directive @code{%locations} is used, the C++ parser supports

-location tracking, see @ref{Locations, , Locations Overview}.  Two
-auxiliary classes define a @code{position}, a single point in a file,
-and a @code{location}, a range composed of a pair of
-@code{position}s (possibly spanning several files).
+location tracking, see @ref{Tracking Locations}.  Two auxiliary classes
+define a @code{position}, a single point in a file, and a @code{location}, a
+range composed of a pair of @code{position}s (possibly spanning several
+files).

 
 @deftypemethod {position} {std::string*} file
 The name of the file.  It will always be handled as a pointer, the
 
 @deftypemethod {position} {std::string*} file
 The name of the file.  It will always be handled as a pointer, the


@@ -9359,8 +9366,8 @@ calcxx_driver::scan_begin ()
     yyin = stdin;
   else if (!(yyin = fopen (file.c_str (), "r")))
     @{
     yyin = stdin;
   else if (!(yyin = fopen (file.c_str (), "r")))
     @{

-      error (std::string ("cannot open ") + file);
-      exit (1);
+      error (std::string ("cannot open ") + file + ": " + strerror(errno));
+      exit (EXIT_FAILURE);

     @}
 @}
 
     @}
 @}
 


@@ -9508,14 +9515,13 @@ can be used to print the semantic values.  This however may change
 @c - class Position
 @c - class Location
 
 @c - class Position
 @c - class Location
 

-When the directive @code{%locations} is used, the Java parser
-supports location tracking, see @ref{Locations, , Locations Overview}.
-An auxiliary user-defined class defines a @dfn{position}, a single point
-in a file; Bison itself defines a class representing a @dfn{location},
-a range composed of a pair of positions (possibly spanning several
-files).  The location class is an inner class of the parser; the name
-is @code{Location} by default, and may also be renamed using
-@code{%define location_type "@var{class-name}"}.
+When the directive @code{%locations} is used, the Java parser supports
+location tracking, see @ref{Tracking Locations}.  An auxiliary user-defined
+class defines a @dfn{position}, a single point in a file; Bison itself
+defines a class representing a @dfn{location}, a range composed of a pair of
+positions (possibly spanning several files).  The location class is an inner
+class of the parser; the name is @code{Location} by default, and may also be
+renamed using @code{%define location_type "@var{class-name}"}.

 
 The location class treats the position as a completely opaque value.
 By default, the class name is @code{Position}, but this can be changed
 
 The location class treats the position as a completely opaque value.
 By default, the class name is @code{Position}, but this can be changed


@@ -10039,11 +10045,17 @@ yyparse (char const *file)
 {
   yyin = fopen (file, "r");
   if (!yyin)
 {
   yyin = fopen (file, "r");
   if (!yyin)

-    exit (2);
+  {
+    perror ("fopen");
+    exit (EXIT_FAILURE);
+  }

   /* One token only.  */
   yylex ();
   if (fclose (yyin) != 0)
   /* One token only.  */
   yylex ();
   if (fclose (yyin) != 0)

-    exit (3);
+  {
+    perror ("fclose");
+    exit (EXIT_FAILURE);
+  }

   return 0;
 }
 
   return 0;
 }
 


@@ -10302,7 +10314,7 @@ transcript of the build session, starting with the invocation of
 send additional files as well (such as `config.h' or `config.cache').
 
 Patches are most welcome, but not required.  That is, do not hesitate to
 send additional files as well (such as `config.h' or `config.cache').
 
 Patches are most welcome, but not required.  That is, do not hesitate to

-send a bug report just because you can not provide a fix.
+send a bug report just because you cannot provide a fix.

 
 Send bug reports to @email{bug-bison@@gnu.org}.
 
 
 Send bug reports to @email{bug-bison@@gnu.org}.
 


@@ -10355,22 +10367,22 @@ See @url{http://lists.gnu.org/}.
 
 @deffn {Variable} @@$
 In an action, the location of the left-hand side of the rule.
 
 @deffn {Variable} @@$
 In an action, the location of the left-hand side of the rule.

-@xref{Locations, , Locations Overview}.
+@xref{Tracking Locations}.

 @end deffn
 
 @deffn {Variable} @@@var{n}
 @end deffn
 
 @deffn {Variable} @@@var{n}

-In an action, the location of the @var{n}-th symbol of the right-hand
-side of the rule.  @xref{Locations, , Locations Overview}.
+In an action, the location of the @var{n}-th symbol of the right-hand side
+of the rule.  @xref{Tracking Locations}.

 @end deffn
 
 @deffn {Variable} @@@var{name}
 @end deffn
 
 @deffn {Variable} @@@var{name}

-In an action, the location of a symbol addressed by name.
-@xref{Locations, , Locations Overview}.
+In an action, the location of a symbol addressed by name.  @xref{Tracking
+Locations}.

 @end deffn
 
 @deffn {Variable} @@[@var{name}]
 @end deffn
 
 @deffn {Variable} @@[@var{name}]

-In an action, the location of a symbol addressed by name.
-@xref{Locations, , Locations Overview}.
+In an action, the location of a symbol addressed by name.  @xref{Tracking
+Locations}.

 @end deffn
 
 @deffn {Variable} $$
 @end deffn
 
 @deffn {Variable} $$