by default (@pxref{Location Type, ,Data Types of Locations}), which is a
four member structure with the following integer fields:
@code{first_line}, @code{first_column}, @code{last_line} and
-@code{last_column}.
+@code{last_column}. By conventions, and in accordance with the GNU
+Coding Standards and common practice, the line and column count both
+start at 1.
@node Ltcalc Rules
@subsection Grammar Rules for @code{ltcalc}
@dots{}
@end smallexample
-@findex %before-definitions
+@findex %before-header
+@findex %start-header
+@findex %after-header
If you've instructed Bison to generate a header file (@pxref{Table of Symbols,
,%defines}), you probably want @code{#include "ptypes.h"} to appear
in that header file as well.
-In that case, use @code{%before-definitions} instead of a @var{Prologue}
-section (@pxref{Table of Symbols, ,%before-definitions}):
+In that case, use @code{%before-header}, @code{%start-header}, and
+@code{%after-header} instead of @var{Prologue} sections
+(@pxref{Table of Symbols, ,%start-header}):
@smallexample
-%@{
+%before-header @{
#include <stdio.h>
-%@}
+@}
-%before-definitions @{
+%start-header @{
#include "ptypes.h"
@}
%union @{
tree t; /* @r{@code{tree} is defined in @file{ptypes.h}.} */
@}
-%@{
+%after-header @{
static void print_token_value (FILE *, int, YYSTYPE);
#define YYPRINT(F, N, L) print_token_value (F, N, L)
-%@}
+@}
@dots{}
@end smallexample
@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
+Bison normally uses the type @code{int} for semantic values if your
+program uses the same data type for all language constructs. To
specify some other type, define @code{YYSTYPE} as a macro, like this:
@example
@itemize @bullet
@item
-Specify the entire collection of possible data types, with the
+Specify the entire collection of possible data types, either by using the
@code{%union} Bison declaration (@pxref{Union Decl, ,The Collection of
-Value Types}).
+Value Types}), or by using a @code{typedef} or a @code{#define} to
+define @code{YYSTYPE} to be a union type whose member names are
+the type tags.
@item
Choose one of those types for each symbol (terminal or nonterminal) for
You can specify the type of locations by defining a macro called
@code{YYLTYPE}, just as you can specify the semantic value type by
-defining @code{YYSTYPE} (@pxref{Value Type}).
+defining a @code{YYSTYPE} macro (@pxref{Value Type}).
When @code{YYLTYPE} is not defined, Bison uses a default structure type with
four members:
@} YYLTYPE;
@end example
+At the beginning of the parsing, Bison initializes all these fields to 1
+for @code{yylloc}.
+
@node Actions and Locations
@subsection Actions and Locations
@cindex location actions
Note that, unlike making a @code{union} declaration in C, you need not write
a semicolon after the closing brace.
+Instead of @code{%union}, you can define and use your own union type
+@code{YYSTYPE} if your grammar contains at least one
+@samp{<@var{type}>} tag. For example, you can put the following into
+a header file @file{parser.h}:
+
+@example
+@group
+union YYSTYPE @{
+ double val;
+ symrec *tptr;
+@};
+typedef union YYSTYPE YYSTYPE;
+@end group
+@end example
+
+@noindent
+and then your grammar can use the following
+instead of @code{%union}:
+
+@example
+@group
+%@{
+#include "parser.h"
+%@}
+%type <val> expr
+%token <tptr> ID
+@end group
+@end example
+
@node Type Decl
@subsection Nonterminal Symbols
@cindex declaring value types, nonterminals
If the parser output file is named @file{@var{name}.c} then this file
is named @file{@var{name}.h}.
-Unless @code{YYSTYPE} is already defined as a macro, the output header
-declares @code{YYSTYPE}. Therefore, if you are using a @code{%union}
+For C parsers, the output header declares @code{YYSTYPE} unless unless
+@code{YYSTYPE} is already defined as a macro or you have used a
+@code{<@var{type}>} tag without using @code{%union}.
+Therefore, if you are using a @code{%union}
(@pxref{Multiple Types, ,More Than One Value Type}) with components that
require other definitions, or if you have defined a @code{YYSTYPE} macro
+or type definition
(@pxref{Value Type, ,Data Types of Semantic Values}), you need to
arrange for these definitions to be propagated to all modules, e.g., by
putting them in a prerequisite header that is included both by your
If you have also used locations, the output header declares
@code{YYLTYPE} and @code{yylloc} using a protocol similar to that of
-@code{YYSTYPE} and @code{yylval}. @xref{Locations, ,Tracking
+the @code{YYSTYPE} macro and @code{yylval}. @xref{Locations, ,Tracking
Locations}.
This output file is normally essential if you wish to put the definition
and to the token type codes. @xref{Token Values, ,Semantic Values of
Tokens}.
-@findex %before-definitions
-@findex %after-definitions
-If you have declared @code{%before-definitions} or @code{%after-definitions},
-the output header also contains their code.
-@xref{Table of Symbols, ,%before-definitions}.
+@findex %start-header
+@findex %end-header
+If you have declared @code{%start-header} or @code{%end-header}, the output
+header also contains their code.
+@xref{Table of Symbols, ,%start-header}.
@end deffn
@deffn {Directive} %destructor
@end example
@noindent
-@findex %before-definitions
+@findex %start-header
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.
-@xref{Table of Symbols, ,%before-definitions}.
+@xref{Table of Symbols, ,%start-header}.
@comment file: calc++-parser.yy
@example
-%before-definitions @{
+%start-header @{
# include <string>
class calcxx_driver;
@}
@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.
+@findex %after-header
+The code between @samp{%after-header @{} and @samp{@}} is output in the
+@file{*.cc} file; it needs detailed knowledge about the driver.
@comment file: calc++-parser.yy
@example
-%@{
+%after-header @{
# include "calc++-driver.hh"
-%@}
+@}
@end example
Start-Symbol}. It cannot be used in the grammar.
@end deffn
-@deffn {Directive} %after-definitions @{@var{code}@}
+@deffn {Directive} %after-header @{@var{code}@}
+Specifies code to be inserted into the code file after the contents of the
+header file.
+@xref{Table of Symbols, ,%start-header}.
+@end deffn
+
+@deffn {Directive} %before-header @{@var{code}@}
+Specifies code to be inserted into the code file before the contents of the
+header file.
+@xref{Table of Symbols, ,%start-header}.
+@end deffn
+
+@deffn {Directive} %end-header @{@var{code}@}
Specifies code to be inserted both into the header file (if generated;
@pxref{Table of Symbols, ,%defines}) and into the code file after any
Bison-generated definitions.
-For details, @xref{Table of Symbols, ,%before-definitions}.
+@xref{Table of Symbols, ,%start-header}.
@end deffn
-@deffn {Directive} %before-definitions @{@var{code}@}
+@deffn {Directive} %start-header @{@var{code}@}
Specifies code to be inserted both into the header file (if generated;
@pxref{Table of Symbols, ,%defines}) and into the code file before any
Bison-generated definitions.
@cindex Prologue
-@findex %after-definitions
+@findex %before-header
@findex %union
-For example, in your grammar file:
+@findex %end-header
+@findex %after-header
+For example, the following declaration order in the grammar file reflects the
+order in which Bison will output these code blocks. However, you are free to
+declare these code blocks in your grammar file in whatever order is most
+convenient for you:
@smallexample
-%@{
- /* A pre-prologue block. For Yacc portability, Bison does not put
- * this in the header file. In the code file, Bison inserts it
- * before any %before-definitions blocks. */
-%@}
-%before-definitions @{
- /* Bison inserts this into both the header file and code file. In
- * both files, the point of insertion is before any Bison-generated
- * token, semantic type, location type, and class definitions.
- * This is a good place to define %union dependencies, for
- * example. */
+%before-header @{
+ /* Bison treats this block like a pre-prologue block: it inserts it
+ * into the code file before the contents of the header file. It
+ * does *not* insert it into the header file. This is a good place
+ * to put #include's that you want at the top of your code file. A
+ * common example is `#include "system.h"'. */
+@}
+%start-header @{
+ /* Bison inserts this block into both the header file and the code
+ * file. In both files, the point of insertion is before any
+ * Bison-generated token, semantic type, location type, and class
+ * definitions. This is a good place to define %union
+ * dependencies, for example. */
@}
%union @{
- /* The first %union, %before-definitions, or %after-definitions
- * in your grammar file separates the pre-prologue blocks from the
- * post-prologue blocks. */
+ /* Unlike the traditional Yacc prologue blocks, the output order
+ * for the %*-header blocks is not affected by their declaration
+ * position relative to any %union in the grammar file. */
@}
-%after-definitions @{
- /* If you want something in the header file and in the code file
- * and it depends on any of the Bison-generated definitions in the
- * header file, put it here. */
+%end-header @{
+ /* Bison inserts this block into both the header file and the code
+ * file. In both files, the point of insertion is after the
+ * Bison-generated definitions. This is a good place to declare or
+ * define public functions or data structures that depend on the
+ * Bison-generated definitions. */
+@}
+%after-header @{
+ /* Bison treats this block like a post-prologue block: it inserts
+ * it into the code file after the contents of the header file. It
+ * does *not* insert it into the header file. This is a good place
+ * to declare or define internal functions or data structures that
+ * depend on the Bison-generated definitions. */
@}
-%@{
- /* A post-prologue block. If you want something in the code file
- * but not in the header file and it depends on Bison-generated
- * definitions, put it here. In the code file, Bison inserts it
- * after any %after-definitions blocks. */
-%@}
@end smallexample
+If you have multiple occurrences of any one of the above declarations, Bison
+will concatenate the contents in declaration order.
+
@xref{Prologue, ,The Prologue}.
@end deffn
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