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Consolidate the 4 prologue alternative directives (%code, %requires,

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%provides, and %code-top) into a single %code directive with an
optional qualifier field.  Discussed at
<http://lists.gnu.org/archive/html/bison-patches/2007-01/msg00012.html>.
* NEWS (2.3a+): Rewrite the existing entry for the prologue
alternatives.
* doc/bison.texinfo (Prologue Alternatives): Update.
(Decl Summary): Update to %code "requires" and %code "provides".
(Calc++ Parser): Update to %code "requires".
(Bison Symbols): Remove entries for %requires, %provides, and
%code-top.  Rewrite %code entry, and add a %code "QUALIFIER" entry.
* data/bison.m4 (b4_user_provides, b4_user_requires): Remove as these
are replaced by b4_percent_code_provides and b4_percent_code_requires,
which are skeleton-specific.
(b4_check_percent_code_qualifiers): New.  A skeleton can use this to
declare what %code qualifiers it supports and to complain if any other
qualifiers were used in the grammar.
* data/glr.cc: Update to use b4_user_code([b4_percent_code_requires])
and b4_user_code([b4_percent_code_provides]) in place of
b4_user_requires and b4_user_provides.
* data/glr.c, data/lalr1.cc, data/push.c, data/yacc.c: Likewise.
Add b4_user_code([b4_percent_code_top]) and
b4_user_code([b4_percent_code]).
Invoke b4_check_percent_code_qualifiers.
* src/parse-gram.y (PERCENT_CODE_TOP, PERCENT_PROVIDES,
PERCENT_REQUIRES): Remove.
(grammar_declaration): Remove RHS's for %code-top, %provides, and
%requires.  Rewrite the %code RHS as the unqualified form defining the
muscle b4_percent_code.  Add another RHS for the qualified %code form,
which defines muscles of the form b4_percent_code_QUALIFIER and the
b4_used_percent_code_qualifiers muscle.
* src/scan-gram.l (PERCENT_CODE_TOP, PERCENT_PROVIDES,
PERCENT_REQUIRES): Remove.
* tests/actions.at (_AT_CHECK_PRINTER_AND_DESTRUCTOR): Update to use
%code "requires" and %code "provides".
* tests/input.at (Reject bad %code qualifiers): New.
This commit is contained in:
Joel E. Denny
2007-01-05 08:14:45 +00:00
parent 95021767a1
commit 8e0a5e9e73
15 changed files with 1060 additions and 983 deletions
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303
doc/bison.texinfo
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@@ -2681,17 +2681,20 @@ feature test macros can affect the behavior of Bison-generated
@cindex Prologue Alternatives
@findex %code
@findex %requires
@findex %provides
@findex %code-top
@findex %code "requires"
@findex %code "provides"
@findex %code "top"
(The prologue alternatives described here are experimental.
More user feedback will help to determine whether they should become permanent
features.)
The functionality of @var{Prologue} sections can often be subtle and
inflexible.
As an alternative, Bison provides a set of more explicit directives:
@code{%code}, @code{%requires}, @code{%provides}, and @code{%code-top}.
As an alternative, Bison provides a %code directive with an explicit qualifier
field, which identifies the purpose of the code and thus the location(s) where
Bison should generate it.
For C/C++, the qualifier can be omitted for the default location, or it can be
"requires", "provides", or "top".
@xref{Table of Symbols,,Bison Symbols}.
Look again at the example of the previous section:
@@ -2723,7 +2726,7 @@ For example, if you decide to override Bison's default definition for
@code{YYLTYPE}, in which @var{Prologue} section should you write your new
definition?
You should write it in the first since Bison will insert that code into the
parser code file @emph{before} the default @code{YYLTYPE} definition.
parser source code file @emph{before} the default @code{YYLTYPE} definition.
In which @var{Prologue} section should you prototype an internal function,
@code{trace_token}, that accepts @code{YYLTYPE} and @code{yytokentype} as
arguments?
@@ -2739,16 +2742,19 @@ Second, what if there is no @code{%union}?
In that case, the second kind of @var{Prologue} section is not available.
This behavior is not intuitive.
To avoid this subtle @code{%union} dependency, rewrite the example using
@code{%code-top} and @code{%code}.
To avoid this subtle @code{%union} dependency, rewrite the example using a
@code{%code "top"} and an unqualified @code{%code}.
Let's go ahead and add the new @code{YYLTYPE} definition and the
@code{trace_token} prototype at the same time:
@smallexample
%code-top @{
%code "top" @{
#define _GNU_SOURCE
#include <stdio.h>
/* The following code really belongs in a %requires; see below. */
/* WARNING: The following code really belongs
* in a %code "requires"; see below. */
#include "ptypes.h"
#define YYLTYPE YYLTYPE
typedef struct YYLTYPE
@@ -2776,33 +2782,34 @@ Let's go ahead and add the new @code{YYLTYPE} definition and the
@end smallexample
@noindent
In this way, @code{%code-top} and @code{%code} achieve the same functionality
as the two kinds of @var{Prologue} sections, but it's always explicit which
kind you intend.
In this way, @code{%code "top"} and the unqualified @code{%code} achieve the
same functionality as the two kinds of @var{Prologue} sections, but it's always
explicit which kind you intend.
Moreover, both kinds are always available even in the absence of @code{%union}.
The @code{%code-top} block above logically contains two parts.
The first two lines need to appear in the parser code file.
The fourth line is required by @code{YYSTYPE} and thus also needs to appear in
the parser code file.
The @code{%code "top"} block above logically contains two parts.
The first two lines before the warning need to appear near the top of the
parser source code file.
The first line after the warning is required by @code{YYSTYPE} and thus also
needs to appear in the parser source code file.
However, if you've instructed Bison to generate a parser header file
(@pxref{Table of Symbols, ,%defines}), you probably want the fourth line to
appear before the @code{YYSTYPE} definition in that header file as well.
Also, the @code{YYLTYPE} definition should appear in the parser header file to
(@pxref{Table of Symbols, ,%defines}), you probably want that line to appear
before the @code{YYSTYPE} definition in that header file as well.
The @code{YYLTYPE} definition should also appear in the parser header file to
override the default @code{YYLTYPE} definition there.
In other words, in the @code{%code-top} block above, all but the first two
lines are dependency code for externally exposed definitions (@code{YYSTYPE}
and @code{YYLTYPE}) required by Bison.
Thus, they belong in one or more @code{%requires}:
In other words, in the @code{%code "top"} block above, all but the first two
lines are dependency code required by the @code{YYSTYPE} and @code{YYLTYPE}
definitions.
Thus, they belong in one or more @code{%code "requires"}:
@smallexample
%code-top @{
%code "top" @{
#define _GNU_SOURCE
#include <stdio.h>
@}
%requires @{
%code "requires" @{
#include "ptypes.h"
@}
%union @{
@@ -2810,7 +2817,7 @@ Thus, they belong in one or more @code{%requires}:
tree t; /* @r{@code{tree} is defined in @file{ptypes.h}.} */
@}
%requires @{
%code "requires" @{
#define YYLTYPE YYLTYPE
typedef struct YYLTYPE
@{
@@ -2834,40 +2841,41 @@ Thus, they belong in one or more @code{%requires}:
@noindent
Now Bison will insert @code{#include "ptypes.h"} and the new @code{YYLTYPE}
definition before the Bison-generated @code{YYSTYPE} and @code{YYLTYPE}
definitions in both the parser code file and the parser header file.
(By the same reasoning, @code{%requires} would also be the appropriate place to
write your own definition for @code{YYSTYPE}.)
definitions in both the parser source code file and the parser header file.
(By the same reasoning, @code{%code "requires"} would also be the appropriate
place to write your own definition for @code{YYSTYPE}.)
When you are writing dependency code for @code{YYSTYPE} and @code{YYLTYPE}, you
should prefer @code{%requires} over @code{%code-top} regardless of whether you
instruct Bison to generate a parser header file.
should prefer @code{%code "requires"} over @code{%code "top"} regardless of
whether you instruct Bison to generate a parser header file.
When you are writing code that you need Bison to insert only into the parser
code file and that has no special need to appear at the top of the code file,
you should prefer @code{%code} over @code{%code-top}.
source code file and that has no special need to appear at the top of that
file, you should prefer the unqualified @code{%code} over @code{%code "top"}.
These practices will make the purpose of each block of your code explicit to
Bison and to other developers reading your grammar file.
Following these practices, we expect @code{%code} and @code{%requires} to be
the most important of the four @var{Prologue} alternative directives discussed
in this section.
Following these practices, we expect the unqualified @code{%code} and
@code{%code "requires"} to be the most important of the four @var{Prologue}
alternatives discussed in this section.
At some point while developing your parser, you might decide to provide
@code{trace_token} to modules that are external to your parser.
Thus, you might wish for Bison to insert the prototype into both the parser
header file and the parser code file.
Since this function is not a dependency of any Bison-required definition (such
as @code{YYSTYPE}), it doesn't make sense to move its prototype to a
@code{%requires}.
header file and the parser source code file.
Since this function is not a dependency required by @code{YYSTYPE} or
@code{YYLTYPE}, it doesn't make sense to move its prototype to a
@code{%code "requires"}.
More importantly, since it depends upon @code{YYLTYPE} and @code{yytokentype},
@code{%requires} is not sufficient.
Instead, move its prototype from the @code{%code} to a @code{%provides}:
@code{%code "requires"} is not sufficient.
Instead, move its prototype from the unqualified @code{%code} to a
@code{%code "provides"}:
@smallexample
%code-top @{
%code "top" @{
#define _GNU_SOURCE
#include <stdio.h>
@}
%requires @{
%code "requires" @{
#include "ptypes.h"
@}
%union @{
@@ -2875,7 +2883,7 @@ Instead, move its prototype from the @code{%code} to a @code{%provides}:
tree t; /* @r{@code{tree} is defined in @file{ptypes.h}.} */
@}
%requires @{
%code "requires" @{
#define YYLTYPE YYLTYPE
typedef struct YYLTYPE
@{
@@ -2887,7 +2895,7 @@ Instead, move its prototype from the @code{%code} to a @code{%provides}:
@} YYLTYPE;
@}
%provides @{
%code "provides" @{
void trace_token (enum yytokentype token, YYLTYPE loc);
@}
@@ -2901,12 +2909,13 @@ Instead, move its prototype from the @code{%code} to a @code{%provides}:
@noindent
Bison will insert the @code{trace_token} prototype into both the parser header
file and the parser code file after the definitions for @code{yytokentype},
@code{YYLTYPE}, and @code{YYSTYPE}.
file and the parser source code file after the definitions for
@code{yytokentype}, @code{YYLTYPE}, and @code{YYSTYPE}.
The above examples are careful to write directives in an order that reflects
the layout of the generated parser code and header files:
@code{%code-top}, @code{%requires}, @code{%provides}, and then @code{%code}.
the layout of the generated parser source code and header files:
@code{%code "top"}, @code{%code "requires"}, @code{%code "provides"}, and then
@code{%code}.
While your grammar files may generally be easier to read if you also follow
this order, Bison does not require it.
Instead, Bison lets you choose an organization that makes sense to you.
@@ -2922,12 +2931,12 @@ For example, you may organize semantic-type-related directives by semantic
type:
@smallexample
%requires @{ #include "type1.h" @}
%code "requires" @{ #include "type1.h" @}
%union @{ type1 field1; @}
%destructor @{ type1_free ($$); @} <field1>
%printer @{ type1_print ($$); @} <field1>
%requires @{ #include "type2.h" @}
%code "requires" @{ #include "type2.h" @}
%union @{ type2 field2; @}
%destructor @{ type2_free ($$); @} <field2>
%printer @{ type2_print ($$); @} <field2>
@@ -2943,13 +2952,14 @@ counter-intuitive manner just because it comes first.
Such an organization is not possible using @var{Prologue} sections.
This section has been concerned with explaining the advantages of the four
@var{Prologue} alternative directives over the original Yacc @var{Prologue}.
@var{Prologue} alternatives over the original Yacc @var{Prologue}.
However, in most cases when using these directives, you shouldn't need to
think about all the low-level ordering issues discussed here.
Instead, you should simply use these directives to label each block of your
code according to its purpose and let Bison handle the ordering.
@code{%code} is the most generic label.
Move code to @code{%requires}, @code{%provides}, or @code{%code-top} as needed.
Move code to @code{%code "requires"}, @code{%code "provides"}, or
@code{%code "top"} as needed.
@node Bison Declarations
@subsection The Bison Declarations Section
@@ -4598,11 +4608,11 @@ typically needs to be able to refer to the above-mentioned declarations
and to the token type codes. @xref{Token Values, ,Semantic Values of
Tokens}.
@findex %requires
@findex %provides
If you have declared @code{%requires} or @code{%provides}, the output
header also contains their code.
@xref{Table of Symbols, ,%requires}.
@findex %code "requires"
@findex %code "provides"
If you have declared @code{%code "requires"} or @code{%code "provides"}, the
output header also contains their code.
@xref{Table of Symbols, ,%code}.
@end deffn
@deffn {Directive} %defines @var{defines-file}
@@ -7863,18 +7873,18 @@ the grammar for.
@end example
@noindent
@findex %requires
@findex %code "requires"
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, ,%requires}.
@xref{Table of Symbols, ,%code}.
@comment file: calc++-parser.yy
@example
%requires @{
%code "requires" @{
# include <string>
class calcxx_driver;
@}
@@ -8634,63 +8644,109 @@ Start-Symbol}. It cannot be used in the grammar.
@end deffn
@deffn {Directive} %code @{@var{code}@}
Other than semantic actions, this is probably the most common place you should
write verbatim code for the parser implementation.
It replaces the traditional Yacc prologue,
@comment For C/C++, it replaces the traditional Yacc prologue,
@code{%@{@var{code}%@}}, for most purposes.
@comment For Java, it inserts code into the parser class.
@findex %code
This is the unqualified form of the @code{%code} directive.
It inserts @var{code} verbatim at the default location in the output.
That default location is determined by the selected target language and/or
parser skeleton.
@cindex Prologue
@findex %union
Compare with @code{%@{@var{code}%@}} (@pxref{Prologue, ,The Prologue})
appearing after the first @code{%union @{@var{code}@}} in a C/C++ based grammar
file.
While Bison will continue to support @code{%@{@var{code}%@}} for backward
compatibility, @code{%code @{@var{code}@}} is cleaner as its functionality does
not depend on its position in the grammar file relative to any
@code{%union @{@var{code}@}}.
Specifically, @code{%code @{@var{code}@}} always inserts your @var{code} into
the parser code file after the usual contents of the parser header file.
For the current C/C++ skeletons, the default location is the parser source code
file after the usual contents of the parser header file.
Thus, @code{%code} replaces the traditional Yacc prologue,
@code{%@{@var{code}%@}}, for most purposes.
For a detailed discussion, see @ref{Prologue Alternatives}.
(Like all the Yacc prologue alternative directives, this directive is
experimental.
@comment For Java, the default location is inside the parser class.
(Like all the Yacc prologue alternatives, this directive is experimental.
More user feedback will help to determine whether it should become a permanent
feature.)
@xref{Prologue Alternatives}.
@end deffn
@deffn {Directive} %code-top @{@var{code}@}
Occasionally it is desirable to insert code near the top of the
@comment Occasionally for C/C++ it is desirable to insert code near the top of the
parser code file.
@deffn {Directive} %code "@var{qualifier}" @{@var{code}@}
This is the qualified form of the @code{%code} directive.
If you need to specify location-sensitive verbatim @var{code} that does not
belong at the default location selected by the unqualified @code{%code} form,
use this form instead.
@var{qualifier} identifies the purpose of @var{code} and thus the location(s)
where Bison should generate it.
Not all values of @var{qualifier} are available for all target languages:
@itemize @bullet
@findex %code "requires"
@item "requires"
@itemize @bullet
@item Language(s): C, C++
@item Purpose: This is the best place to write dependency code required for
@code{YYSTYPE} and @code{YYLTYPE}.
In other words, it's the best place to define types referenced in @code{%union}
directives, and it's the best place to override Bison's default @code{YYSTYPE}
and @code{YYLTYPE} definitions.
@item Location(s): The parser header file and the parser source code file
before the Bison-generated @code{YYSTYPE} and @code{YYLTYPE} definitions.
@end itemize
@item "provides"
@findex %code "provides"
@itemize @bullet
@item Language(s): C, C++
@item Purpose: This is the best place to write additional definitions and
declarations that should be provided to other modules.
@item Location(s): The parser header file and the parser source code file after
the Bison-generated @code{YYSTYPE}, @code{YYLTYPE}, and token definitions.
@end itemize
@item "top"
@findex %code "top"
@itemize @bullet
@item Language(s): C, C++
@item Purpose: The unqualified @code{%code} or @code{%code "requires"} should
usually be more appropriate than @code{%code "top"}.
However, occasionally it is necessary to insert code much nearer the top of the
parser source code file.
For example:
@smallexample
%code-top @{
%code "top" @{
#define _GNU_SOURCE
#include <stdio.h>
@}
@end smallexample
@comment @noindent
@comment For Java, @code{%code-top @{@var{code}@}} is currently unused.
@item Location(s): Near the top of the parser source code file.
@end itemize
@ignore
@item "imports"
@findex %code "imports"
@cindex Prologue
@findex %union
Compare with @code{%@{@var{code}%@}} appearing before the first
@code{%union @{@var{code}@}} in a C/C++ based grammar file.
@code{%code-top @{@var{code}@}} is cleaner as its functionality does not depend
on its position in the grammar file relative to any
@code{%union @{@var{code}@}}.
@itemize @bullet
@item Language(s): Java
(Like all the Yacc prologue alternative directives, this directive is
experimental.
@item Purpose: This is the best place to write Java import directives.
@item Location(s): The parser Java file after any Java package directive and
before any class definitions.
@end itemize
@end ignore
@end itemize
(Like all the Yacc prologue alternatives, this directive is experimental.
More user feedback will help to determine whether it should become a permanent
feature.)
@xref{Prologue Alternatives}.
@cindex Prologue
For a detailed discussion of how to use @code{%code} in place of the
traditional Yacc prologue for C/C++, see @ref{Prologue Alternatives}.
@end deffn
@deffn {Directive} %debug
@@ -8826,24 +8882,6 @@ Bison declaration to assign a precedence to a specific rule.
@xref{Contextual Precedence, ,Context-Dependent Precedence}.
@end deffn
@deffn {Directive} %provides @{@var{code}@}
This is the right place to write additional definitions you would like Bison to
expose externally.
That is, this directive inserts your @var{code} both into the parser header
@comment For C/C++, this directive inserts your @var{code} both into the parser header
file (if generated; @pxref{Table of Symbols, ,%defines}) and into the parser
code file after Bison's required definitions.
@comment For Java, it inserts your @var{code} into the parser java file after the parser
@comment class.
(Like all the Yacc prologue alternative directives, this directive is
experimental.
More user feedback will help to determine whether it should become a permanent
feature.)
@xref{Prologue Alternatives}.
@end deffn
@deffn {Directive} %pure-parser
Bison declaration to request a pure (reentrant) parser.
@xref{Pure Decl, ,A Pure (Reentrant) Parser}.
@@ -8854,35 +8892,6 @@ Require version @var{version} or higher of Bison. @xref{Require Decl, ,
Require a Version of Bison}.
@end deffn
@deffn {Directive} %requires @{@var{code}@}
This is the right place to write dependency code for externally exposed
definitions required by Bison.
Such exposed definitions are those usually appearing in the parser
@comment For C/C++, such exposed definitions are those usually appearing in the parser
header file.
Thus, this is the right place to define types referenced in
@code{%union @{@var{code}@}} directives, and it is the right place to override
Bison's default @code{YYSTYPE} and @code{YYLTYPE} definitions.
@comment For Java, this is the right place to write import directives.
@cindex Prologue
@findex %union
Compare with @code{%@{@var{code}%@}} (@pxref{Prologue, ,The Prologue})
appearing before the first @code{%union @{@var{code}@}} in a C/C++ based
grammar file.
Unlike @code{%@{@var{code}%@}}, @code{%requires @{@var{code}@}} inserts your
@var{code} both into the parser code file and into the parser header file (if
generated; @pxref{Table of Symbols, ,%defines}) since Bison's required
definitions should depend on it in both places.
(Like all the Yacc prologue alternative directives, this directive is
experimental.
More user feedback will help to determine whether it should become a permanent
feature.)
@xref{Prologue Alternatives}.
@end deffn
@deffn {Directive} %right
Bison declaration to assign right associativity to token(s).
@xref{Precedence Decl, ,Operator Precedence}.