* Value Type:: Specifying one data type for all semantic values.
* Multiple Types:: Specifying several alternative data types.
+* Union Decl:: Declaring the set of all semantic value types.
+* Structured Value Type:: Providing a structured semantic value type.
* Actions:: An action is the semantic definition of a grammar rule.
* Action Types:: Specifying data types for actions to operate on.
* Mid-Rule Actions:: Most actions go at the end of a rule.
* 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.
* Type Decl:: Declaring the choice of type for a nonterminal symbol.
* Initial Action Decl:: Code run before parsing starts.
* Destructor Decl:: Declaring how symbols are freed.
The @code{%union} declaration specifies the entire list of possible types;
this is instead of defining @code{api.value.type}. The allowable types are now
double-floats (for @code{exp} and @code{NUM}) and pointers to entries in
-the symbol table. @xref{Union Decl, ,The Collection of Value Types}.
+the symbol table. @xref{Union Decl, ,The Union Declaration}.
Since values can now have various types, it is necessary to associate a
type with each grammar symbol whose semantic value is used. These symbols
@menu
* Value Type:: Specifying one data type for all semantic values.
* Multiple Types:: Specifying several alternative data types.
+* Union Decl:: Declaring the set of all semantic value types.
+* Structured Value Type:: Providing a structured semantic value type.
* Actions:: An action is the semantic definition of a grammar rule.
* Action Types:: Specifying data types for actions to operate on.
* Mid-Rule Actions:: Most actions go at the end of a rule.
@itemize @bullet
@item
-Specify the entire collection of possible data types, either by using the
-@code{%union} Bison declaration (@pxref{Union Decl, ,The Collection of
-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.
+Specify the entire collection of possible data types. There are several
+options:
+@itemize @bullet
+@item
+use the @code{%union} Bison declaration (@pxref{Union Decl, ,The Union
+Declaration});
+
+@item
+define the @code{%define} variable @code{api.value.type} to be a union type
+whose members are the type tags (@pxref{Structured Value Type,, Providing a
+Structured Semantic Value Type});
+
+@item
+use a @code{typedef} or a @code{#define} to define @code{YYSTYPE} to be a
+union type whose member names are the type tags.
+@end itemize
@item
Choose one of those types for each symbol (terminal or nonterminal) for
Decl, ,Nonterminal Symbols}).
@end itemize
+@node Union Decl
+@subsection The Union Declaration
+@cindex declaring value types
+@cindex value types, declaring
+@findex %union
+
+The @code{%union} declaration specifies the entire collection of possible
+data types for semantic values. The keyword @code{%union} is followed by
+braced code containing the same thing that goes inside a @code{union} in C@.
+
+For example:
+
+@example
+@group
+%union @{
+ double val;
+ symrec *tptr;
+@}
+@end group
+@end example
+
+@noindent
+This says that the two alternative types are @code{double} and @code{symrec
+*}. They are given names @code{val} and @code{tptr}; these names are used
+in the @code{%token} and @code{%type} declarations to pick one of the types
+for a terminal or nonterminal symbol (@pxref{Type Decl, ,Nonterminal Symbols}).
+
+As an extension to POSIX, a tag is allowed after the @code{%union}. For
+example:
+
+@example
+@group
+%union value @{
+ double val;
+ symrec *tptr;
+@}
+@end group
+@end example
+
+@noindent
+specifies the union tag @code{value}, so the corresponding C type is
+@code{union value}. If you do not specify a tag, it defaults to
+@code{YYSTYPE}.
+
+As another extension to POSIX, you may specify multiple @code{%union}
+declarations; their contents are concatenated. However, only the first
+@code{%union} declaration can specify a tag.
+
+Note that, unlike making a @code{union} declaration in C, you need not write
+a semicolon after the closing brace.
+
+@node Structured Value Type
+@subsection Providing a Structured Semantic Value Type
+@cindex declaring value types
+@cindex value types, declaring
+@findex %union
+
+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;
+@};
+@end group
+@end example
+
+@noindent
+and then your grammar can use the following instead of @code{%union}:
+
+@example
+@group
+%@{
+#include "parser.h"
+%@}
+%define api.value.type "union YYSTYPE"
+%type <val> expr
+%token <tptr> ID
+@end group
+@end example
+
+Actually, you may also provide a @code{struct} rather that a @code{union},
+which may be handy if you want to track information for every symbol (such
+as preceding comments).
+
+The type you provide may even be structured and include pointers, in which
+case the type tags you provide may be composite, with @samp{.} and @samp{->}
+operators.
+
@node Actions
@subsection Actions
@cindex action
* 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.
* Type Decl:: Declaring the choice of type for a nonterminal symbol.
* Initial Action Decl:: Code run before parsing starts.
* Destructor Decl:: Declaring how symbols are freed.
%left OR 134 "<=" 135 // Declares 134 for OR and 135 for "<=".
@end example
-@node Union Decl
-@subsection The Collection of Value Types
-@cindex declaring value types
-@cindex value types, declaring
-@findex %union
-
-The @code{%union} declaration specifies the entire collection of
-possible data types for semantic values. The keyword @code{%union} is
-followed by braced code containing the same thing that goes inside a
-@code{union} in C@.
-
-For example:
-
-@example
-@group
-%union @{
- double val;
- symrec *tptr;
-@}
-@end group
-@end example
-
-@noindent
-This says that the two alternative types are @code{double} and @code{symrec
-*}. They are given names @code{val} and @code{tptr}; these names are used
-in the @code{%token} and @code{%type} declarations to pick one of the types
-for a terminal or nonterminal symbol (@pxref{Type Decl, ,Nonterminal Symbols}).
-
-As an extension to POSIX, a tag is allowed after the
-@code{union}. For example:
-
-@example
-@group
-%union value @{
- double val;
- symrec *tptr;
-@}
-@end group
-@end example
-
-@noindent
-specifies the union tag @code{value}, so the corresponding C type is
-@code{union value}. If you do not specify a tag, it defaults to
-@code{YYSTYPE}.
-
-As another extension to POSIX, you may specify multiple
-@code{%union} declarations; their contents are concatenated. However,
-only the first @code{%union} declaration can specify a tag.
-
-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;
-@};
-@end group
-@end example
-
-@noindent
-and then your grammar can use the following instead of @code{%union}:
-
-@example
-@group
-%@{
-#include "parser.h"
-%@}
-%define api.value.type "union YYSTYPE"
-%type <val> expr
-%token <tptr> ID
-@end group
-@end example
-
@node Type Decl
@subsection Nonterminal Symbols
@cindex declaring value types, nonterminals
@noindent
Here @var{nonterminal} is the name of a nonterminal symbol, and
@var{type} is the name given in the @code{%union} to the alternative
-that you want (@pxref{Union Decl, ,The Collection of Value Types}). You
+that you want (@pxref{Union Decl, ,The Union Declaration}). You
can give any number of nonterminal symbols in the same @code{%type}
declaration, if they have the same value type. Use spaces to separate
the symbol names.
@deffn {Directive} %union
Declare the collection of data types that semantic values may have
-(@pxref{Union Decl, ,The Collection of Value Types}).
+(@pxref{Union Decl, ,The Union Declaration}).
@end deffn
@deffn {Directive} %token
@item @code{%union} (C, C++)
The type is defined thanks to the @code{%union} directive. You don't have
to define @code{api.value.type} in that case, using @code{%union} suffices.
-@xref{Union Decl, ,The Collection of Value Types}.
+@xref{Union Decl, ,The Union Declaration}.
For instance:
@example
%define api.value.type "%union"
When you are using multiple data types, @code{yylval}'s type is a union
made from the @code{%union} declaration (@pxref{Union Decl, ,The
-Collection of Value Types}). So when you store a token's value, you
+Union Declaration}). So when you store a token's value, you
must use the proper member of the union. If the @code{%union}
declaration looks like this:
@subsubsection C++ Unions
The @code{%union} directive works as for C, see @ref{Union Decl, ,The
-Collection of Value Types}. In particular it produces a genuine
+Union Declaration}. In particular it produces a genuine
@code{union}, which have a few specific features in C++.
@itemize @minus
@item
@deffn {Directive} %union
Bison declaration to specify several possible data types for semantic
-values. @xref{Union Decl, ,The Collection of Value Types}.
+values. @xref{Union Decl, ,The Union Declaration}.
@end deffn
@deffn {Macro} YYABORT
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