@ifinfo
This file documents the Bison parser generator.
-Copyright (C) 1988, 1989, 1990, 1991, 1992, 1993, 1995, 1998, 1999, 2000
+Copyright (C) 1988, 1989, 1990, 1991, 1992, 1993, 1995, 1998, 1999,
+2000, 2001
Free Software Foundation, Inc.
Permission is granted to make and distribute verbatim copies of
@page
@vskip 0pt plus 1filll
Copyright @copyright{} 1988, 1989, 1990, 1991, 1992, 1993, 1995, 1998,
-1999, 2000
+1999, 2000, 2001
Free Software Foundation, Inc.
@sp 2
practical conditions for using Bison match the practical conditions for
using the other GNU tools.
-@node Copying, Concepts, Conditions, Top
-@unnumbered GNU GENERAL PUBLIC LICENSE
-@center Version 2, June 1991
-
-@display
-Copyright @copyright{} 1989, 1991 Free Software Foundation, Inc.
-59 Temple Place - Suite 330, Boston, MA 02111-1307, USA
-
-Everyone is permitted to copy and distribute verbatim copies
-of this license document, but changing it is not allowed.
-@end display
-
-@unnumberedsec Preamble
-
- The licenses for most software are designed to take away your
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-License is intended to guarantee your freedom to share and change free
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-@iftex
-@unnumberedsec TERMS AND CONDITIONS FOR COPYING, DISTRIBUTION AND MODIFICATION
-@end iftex
-@ifinfo
-@center TERMS AND CONDITIONS FOR COPYING, DISTRIBUTION AND MODIFICATION
-@end ifinfo
-
-@enumerate 0
-@item
-This License applies to any program or other work which contains
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-@enumerate a
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-@enumerate a
-@item
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-If, as a consequence of a court judgment or allegation of patent
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-@heading NO WARRANTY
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-@ifinfo
-@center NO WARRANTY
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-BECAUSE THE PROGRAM IS LICENSED FREE OF CHARGE, THERE IS NO WARRANTY
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-
-@iftex
-@heading END OF TERMS AND CONDITIONS
-@end iftex
-@ifinfo
-@center END OF TERMS AND CONDITIONS
-@end ifinfo
-
-@page
-@unnumberedsec How to Apply These Terms to Your New Programs
-
- If you develop a new program, and you want it to be of the greatest
-possible use to the public, the best way to achieve this is to make it
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-@end smallexample
-
-Also add information on how to contact you by electronic and paper mail.
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-Gnomovision comes with ABSOLUTELY NO WARRANTY; for details
-type `show w'.
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-@end smallexample
-
-The hypothetical commands @samp{show w} and @samp{show c} should show
-the appropriate parts of the General Public License. Of course, the
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-
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-@smallexample
-Yoyodyne, Inc., hereby disclaims all copyright interest in the program
-`Gnomovision' (which makes passes at compilers) written by James Hacker.
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-@var{signature of Ty Coon}, 1 April 1989
-Ty Coon, President of Vice
-@end smallexample
-
-This General Public License does not permit incorporating your program into
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-consider it more useful to permit linking proprietary applications with the
-library. If this is what you want to do, use the GNU Library General
-Public License instead of this License.
+@include gpl.texi
@node Concepts, Examples, Copying, Top
@chapter The Concepts of Bison
a semantic value (the value of an integer,
the name of an identifier, etc.).
* Semantic Actions:: Each rule can have an action containing C code.
+* Locations Overview:: Tracking Locations.
* Bison Parser:: What are Bison's input and output,
how is the output used?
* Stages:: Stages in writing and running Bison grammars.
language, an expression typically has a semantic value that is a tree
structure describing the meaning of the expression.
-@node Semantic Actions, Bison Parser, Semantic Values, Concepts
+@node Semantic Actions, Locations Overview, Semantic Values, Concepts
@section Semantic Actions
@cindex semantic actions
@cindex actions, semantic
The action says how to produce the semantic value of the sum expression
from the values of the two subexpressions.
-@node Bison Parser, Stages, Semantic Actions, Concepts
+@node Locations Overview, Bison Parser, Semantic Actions, Concepts
+@section Locations
+@cindex location
+@cindex textual position
+@cindex position, textual
+
+Many applications, like interpreters or compilers, have to produce verbose
+and useful error messages. To achieve this, one must be able to keep track of
+the @dfn{textual position}, 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
+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).
+
+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
+is @code{@@$}, while the locations of the subexpressions are @code{@@1} and
+@code{@@3}.
+
+When a rule is matched, a default action is used to compute the semantic value
+of its left hand side (@pxref{Actions}). In the same way, another default
+action is used for locations. However, the action for locations is general
+enough for most cases, meaning there is usually no need to describe for each
+rule how @code{@@$} should be formed. When building a new location for a given
+grouping, the default behavior of the output parser is to take the beginning
+of the first symbol, and the end of the last symbol.
+
+@node Bison Parser, Stages, Locations Overview, Concepts
@section Bison Output: the Parser File
@cindex Bison parser
@cindex Bison utility
C-language function that recognizes correct instances of the grammar.
The Bison grammar input file conventionally has a name ending in @samp{.y}.
+@xref{Invocation, ,Invoking Bison}.
@menu
* Grammar Outline:: Overall layout of the grammar file.
* Rules:: How to write grammar rules.
* Recursion:: Writing recursive rules.
* Semantics:: Semantic values and actions.
+* Locations:: Locations and actions.
* Declarations:: All kinds of Bison declarations are described here.
* Multiple Parsers:: Putting more than one Bison parser in one program.
@end menu
defines two mutually-recursive nonterminals, since each refers to the
other.
-@node Semantics, Declarations, Recursion, Grammar File
+@node Semantics, Locations, Recursion, Grammar File
@section Defining Language Semantics
@cindex defining language semantics
@cindex language semantics, defining
its value with an assignment to @code{$$}, and actions later in the rule
can refer to the value using @code{$@var{n}}. Since there is no symbol
to name the action, there is no way to declare a data type for the value
-in advance, so you must use the @samp{$<@dots{}>} construct to specify a
-data type each time you refer to this value.
+in advance, so you must use the @samp{$<@dots{}>@var{n}} construct to
+specify a data type each time you refer to this value.
There is no way to set the value of the entire rule with a mid-rule
action, because assignments to @code{$$} do not have that effect. The
converted to an end-of-rule action in this way, and this is what Bison
actually does to implement mid-rule actions.
-@node Declarations, Multiple Parsers, Semantics, Grammar File
+@node Locations, Declarations, Semantics, Grammar File
+@section Tracking Locations
+@cindex location
+@cindex textual position
+@cindex position, textual
+
+Though grammar rules and semantic actions are enough to write a fully
+functional parser, it can be useful to process some additionnal informations,
+especially symbol locations.
+
+@c (terminal or not) ?
+
+The way locations are handled is defined by providing a data type, and actions
+to take when rules are matched.
+
+@menu
+* Location Type:: Specifying a data type for locations.
+* Actions and Locations:: Using locations in actions.
+* Location Default Action:: Defining a general way to compute locations.
+@end menu
+
+@node Location Type, Actions and Locations, , Locations
+@subsection Data Type of Locations
+@cindex data type of locations
+@cindex default location type
+
+Defining a data type for locations is much simpler than for semantic values,
+since all tokens and groupings always use the same type.
+
+The type of locations is specified by defining a macro called @code{YYLTYPE}.
+When @code{YYLTYPE} is not defined, Bison uses a default structure type with
+four members:
+
+@example
+struct
+@{
+ int first_line;
+ int first_column;
+ int last_line;
+ int last_column;
+@}
+@end example
+
+@node Actions and Locations, Location Default Action, Location Type, Locations
+@subsection Actions and Locations
+@cindex location actions
+@cindex actions, location
+@vindex @@$
+@vindex @@@var{n}
+
+Actions are not only useful for defining language semantics, but also for
+describing the behavior of the output parser with locations.
+
+The most obvious way for building locations of syntactic groupings is very
+similar to the way semantic values are computed. In a given rule, several
+constructs can be used to access the locations of the elements being matched.
+The location of the @var{n}th component of the right hand side is
+@code{@@@var{n}}, while the location of the left hand side grouping is
+@code{@@$}.
+
+Here is a basic example using the default data type for locations:
+
+@example
+@group
+exp: @dots{}
+ | exp '/' exp
+ @{
+ @@$.first_column = @@1.first_column;
+ @@$.first_line = @@1.first_line;
+ @@$.last_column = @@3.last_column;
+ @@$.last_line = @@3.last_line;
+ if ($3)
+ $$ = $1 / $3;
+ else
+ @{
+ $$ = 1;
+ printf("Division by zero, l%d,c%d-l%d,c%d",
+ @@3.first_line, @@3.first_column,
+ @@3.last_line, @@3.last_column);
+ @}
+ @}
+@end group
+@end example
+
+As for semantic values, there is a default action for locations that is
+run each time a rule is matched. It sets the beginning of @code{@@$} to the
+beginning of the first symbol, and the end of @code{@@$} to the end of the
+last symbol.
+
+With this default action, the location tracking can be fully automatic. The
+example above simply rewrites this way:
+
+@example
+@group
+exp: @dots{}
+ | exp '/' exp
+ @{
+ if ($3)
+ $$ = $1 / $3;
+ else
+ @{
+ $$ = 1;
+ printf("Division by zero, l%d,c%d-l%d,c%d",
+ @@3.first_line, @@3.first_column,
+ @@3.last_line, @@3.last_column);
+ @}
+ @}
+@end group
+@end example
+
+@node Location Default Action, , Actions and Locations, Locations
+@subsection Default Action for Locations
+@vindex YYLLOC_DEFAULT
+
+Actually, actions are not the best place to compute locations. Since locations
+are much more general than semantic values, there is room in the output parser
+to redefine the default action to take for each rule. The
+@code{YYLLOC_DEFAULT} macro is called each time a rule is matched, before the
+associated action is run.
+
+Most of the time, this macro is general enough to suppress location
+dedicated code from semantic actions.
+
+The @code{YYLLOC_DEFAULT} macro takes three parameters. The first one is
+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:
+
+@example
+@group
+#define YYLLOC_DEFAULT(Current, Rhs, N) \
+ Current.last_line = Rhs[N].last_line; \
+ Current.last_column = Rhs[N].last_column;
+@end group
+@end example
+
+When defining @code{YYLLOC_DEFAULT}, you should consider that:
+
+@itemize @bullet
+@item
+All arguments are free of side-effects. However, only the first one (the
+result) should be modified by @code{YYLLOC_DEFAULT}.
+
+@item
+Before @code{YYLLOC_DEFAULT} is executed, the output parser sets @code{@@$}
+to @code{@@1}.
+
+@item
+For consistency with semantic actions, valid indexes for the location array
+range from 1 to @var{n}.
+@end itemize
+
+@node Declarations, Multiple Parsers, Locations, Grammar File
@section Bison Declarations
@cindex declarations, Bison
@cindex Bison declarations
@subsection Textual Positions of Tokens
@vindex yylloc
-If you are using the @samp{@@@var{n}}-feature (@pxref{Action Features,
-,Special Features for Use in Actions}) in actions to keep track of the
+If you are using the @samp{@@@var{n}}-feature (@pxref{Locations, ,
+Tracking Locations}) in actions to keep track of the
textual locations of tokens and groupings, then you must provide this
information in @code{yylex}. The function @code{yyparse} expects to
find the textual location of a token just parsed in the global variable
@code{yylloc}. So @code{yylex} must store the proper data in that
-variable. The value of @code{yylloc} is a structure and you need only
+variable.
+
+By default, the value of @code{yylloc} is a structure and you need only
initialize the members that are going to be used by the actions. The
four members are called @code{first_line}, @code{first_column},
@code{last_line} and @code{last_column}. Note that the use of this
errors. This is useful primarily in error rules.
@xref{Error Recovery}.
-@item @@@var{n}
-@findex @@@var{n}
-Acts like a structure variable containing information on the line
-numbers and column numbers of the @var{n}th component of the current
-rule. The structure has four members, like this:
+@item @@$
+@findex @@$
+Acts like a structure variable containing information on the textual position
+of the grouping made by the current rule. @xref{Locations, ,
+Tracking Locations}.
-@example
-struct @{
- int first_line, last_line;
- int first_column, last_column;
-@};
-@end example
+@c Check if those paragraphs are still useful or not.
+
+@c @example
+@c struct @{
+@c int first_line, last_line;
+@c int first_column, last_column;
+@c @};
+@c @end example
-Thus, to get the starting line number of the third component, you would
-use @samp{@@3.first_line}.
+@c Thus, to get the starting line number of the third component, you would
+@c use @samp{@@3.first_line}.
-In order for the members of this structure to contain valid information,
-you must make @code{yylex} supply this information about each token.
-If you need only certain members, then @code{yylex} need only fill in
-those members.
+@c In order for the members of this structure to contain valid information,
+@c you must make @code{yylex} supply this information about each token.
+@c If you need only certain members, then @code{yylex} need only fill in
+@c those members.
+
+@c The use of this feature makes the parser noticeably slower.
+
+@item @@@var{n}
+@findex @@@var{n}
+Acts like a structure variable containing information on the textual position
+of the @var{n}th component of the current rule. @xref{Locations, ,
+Tracking Locations}.
-The use of this feature makes the parser noticeably slower.
@end table
@node Algorithm, Error Recovery, Interface, Top
@samp{.y}. The parser file's name is made by replacing the @samp{.y}
with @samp{.tab.c}. Thus, the @samp{bison foo.y} filename yields
@file{foo.tab.c}, and the @samp{bison hack/foo.y} filename yields
-@file{hack/foo.tab.c}.@refill
+@file{hack/foo.tab.c}. It's is also possible, in case you are writting
+C++ code instead of C in your grammar file, to name it @file{foo.ypp}
+or @file{foo.y++}. Then, the output files will take an extention like
+the given one as input (repectively @file{foo.tab.cpp} and @file{foo.tab.c++}).
+This feature takes effect with all options that manipulate filenames like
+@samp{-o} or @samp{-d}.
+
+For example :
+
+@example
+bison -d @var{infile.yxx}
+@end example
+@noindent
+will produce @file{infile.tab.cxx} and @file{infile.tab.hxx}. and
+
+@example
+bison -d @var{infile.y} -o @var{output.c++}
+@end example
+@noindent
+will produce @file{output.c++} and @file{outfile.h++}.
+
@menu
* Bison Options:: All the options described in detail,
@item YYLTYPE
Macro for the data type of @code{yylloc}; a structure with four
-members. @xref{Token Positions, ,Textual Positions of Tokens}.
+members. @xref{Location Type, , Data Types of Locations}.
@item yyltype
Default value for YYLTYPE.
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