Let the initial-action act on the look-ahead, and use it for the

"initial push" (corresponding to an hypothetical beginning-of-file).
And let lalr1.cc honor %initial-action.
* doc/bison.texinfo (Initial Action Decl): Clarify, and add an
example.
* data/lalr1.cc (Parser::initlocation_): Remove, bad experiment.
(Parser::Parser): Remove the ctor that used to initialize it.
(Parser::parse): Like in the other skeletons, issue the "starting
parse" message before any action.
Honor %initial-action.
Initialize the stacks with the lookahead.
* data/yacc.c: Let $$ and @$ in %initial-action designate the
look-ahead.
Push them in the stacks.
* tests/actions.at, tests/calc.at: Adjust the C++ ctor invocations.

ChangeLog

@@ -1,3 +1,22 @@
+2004-09-20  Akim Demaille  <akim@epita.fr>
+
+	Let the initial-action act on the look-ahead, and use it for the
+	"initial push" (corresponding to an hypothetical beginning-of-file).
+	And let lalr1.cc honor %initial-action.
+
+	* doc/bison.texinfo (Initial Action Decl): Clarify, and add an
+	example.
+	* data/lalr1.cc (Parser::initlocation_): Remove, bad experiment.
+	(Parser::Parser): Remove the ctor that used to initialize it.
+	(Parser::parse): Like in the other skeletons, issue the "starting
+	parse" message before any action.
+	Honor %initial-action.
+	Initialize the stacks with the lookahead.
+	* data/yacc.c: Let $$ and @$ in %initial-action designate the
+	look-ahead.
+	Push them in the stacks.
+	* tests/actions.at, tests/calc.at: Adjust the C++ ctor invocations.
+
 2004-09-20  Akim Demaille  <akim@epita.fr>
 
 	* doc/bison.texinfo (Initial Action Decl): New.

data/lalr1.cc

@@ -218,17 +218,9 @@ namespace yy
     typedef Stack< SemanticType > SemanticStack;
     typedef Stack< LocationType > LocationStack;
 
-#if YYLSP_NEEDED
-    ]b4_parser_class_name[ (bool debug,
-	    LocationType initlocation][]b4_param[]b4_parse_param_decl[) :
-      ]b4_constructor[][debug_ (debug),
-      cdebug_ (std::cerr),
-      initlocation_ (initlocation)]b4_parse_param_cons[
-#else
     ]b4_parser_class_name[ (bool debug][]b4_param[]b4_parse_param_decl[) :
       ]b4_constructor[][debug_ (debug),
       cdebug_ (std::cerr)]b4_parse_param_cons[
-#endif
     {
     }
 
@@ -325,18 +317,17 @@ namespace yy
     /* Message.  */
     std::string message;
 
-    /* Semantic value and location of look-ahead token.  */
+    /// Semantic value of the look-ahead.
     SemanticType value;
+    /// Location of the look-ahead.
     LocationType location;
     /// The locations where the error started and ended.
     Location error_range_[2];
 
-    /* @@$ and $$.  */
+    /// $$.
     SemanticType yyval;
+    /// @@$.
     LocationType yyloc;
-
-    /* Initial location.  */
-    LocationType initlocation_;
 ]b4_parse_param_vars[
   };
 }
@@ -446,24 +437,34 @@ yy::]b4_parser_class_name[::pop (unsigned int n)
 int
 yy::]b4_parser_class_name[::parse ()
 {
+  YYCDEBUG << "Starting parse" << std::endl;
+
   nerrs_ = 0;
   errstatus_ = 0;
 
-  /* Initialize the stacks.  The initial state will be pushed in
-     yynewstate, since the latter expects the semantical and the
-     location values to have been already stored, initialize these
-     stacks with a primary value.  */
-  state_stack_ = StateStack (0);
-  semantic_stack_ = SemanticStack (1);
-  location_stack_ = LocationStack (1);
-
   /* Start.  */
   state_ = 0;
   looka_ = empty_;
-#if YYLSP_NEEDED
+
-  location = initlocation_;
+]m4_ifdef([b4_initial_action], [
-#endif
+m4_pushdef([b4_at_dollar],     [location])dnl
-  YYCDEBUG << "Starting parse" << std::endl;
+m4_pushdef([b4_dollar_dollar], [value])dnl
+  /* User initialization code. */
+  b4_initial_action
+m4_popdef([b4_dollar_dollar])dnl
+m4_popdef([b4_at_dollar])dnl
+/* Line __line__ of yacc.c.  */
+b4_syncline([@oline@], [@ofile@])])dnl
+
+[  /* Initialize the stacks.  The initial state will be pushed in
+     yynewstate, since the latter expects the semantical and the
+     location values to have been already stored, initialize these
+     stacks with a primary value.  */
+  state_stack_ = StateStack (0);
+  semantic_stack_ = SemanticStack (0);
+  location_stack_ = LocationStack (0);
+  semantic_stack_.push (value);
+  location_stack_.push (location);
 
   /* New state.  */
 yynewstate:

data/yacc.c

@@ -821,20 +821,23 @@ b4_c_function_def([yyparse], [int], b4_parse_param)
 ]b4_location_if([[  yylsp = yyls;
 #if YYLTYPE_IS_TRIVIAL
   /* Initialize the default location before parsing starts.  */
-  yyls[0].first_line   = yyls[0].last_line   = 1;
+  yylloc.first_line   = yylloc.last_line   = 1;
-  yyls[0].first_column = yyls[0].last_column = 0;
+  yylloc.first_column = yylloc.last_column = 0;
 #endif
 ]])
 m4_ifdef([b4_initial_action], [
-m4_pushdef([b4_at_dollar],     [(*yylsp)])dnl
+m4_pushdef([b4_at_dollar],     [(yylloc)])dnl
-m4_pushdef([b4_dollar_dollar], [(*yyvsp)])dnl
+m4_pushdef([b4_dollar_dollar], [(yylval)])dnl
   /* User initialization code. */
   b4_initial_action
 m4_popdef([b4_dollar_dollar])dnl
 m4_popdef([b4_at_dollar])dnl
 /* Line __line__ of yacc.c.  */
 b4_syncline([@oline@], [@ofile@])])dnl
-
+[
+  yyvsp[0] = yylval;
+]b4_location_if([[    yylsp[0] = yylloc;
+]])
 [  goto yysetstate;
 
 /*------------------------------------------------------------.

doc/bison.texinfo

@@ -3742,10 +3742,21 @@ code.
 @deffn {Directive} %initial-action @{ @var{code} @}
 @findex %initial-action
 Declare that the @var{code} must be invoked before parsing each time
-@code{yyparse} is called.  The @var{code} may use @code{@@$} to
+@code{yyparse} is called.  The @var{code} may use @code{$$} and
-designate the initial location, and the @code{%parse-param}.
+@code{@@$} --- initial value and location of the look-ahead --- and the
+@code{%parse-param}.
 @end deffn
 
+For instance, if your locations use a file name, you may use
+
+@example
+%parse-param @{ const char *filename @};
+%initial-action
+@{
+  @@$.begin.filename = @@$.end.filename = filename;
+@};
+@end example
+
 
 @node Destructor Decl
 @subsection Freeing Discarded Symbols
@@ -3822,7 +3833,7 @@ stacked symbols popped during the first phase of error recovery,
 @item
 incoming terminals during the second phase of error recovery,
 @item
-the current lookahead when the parser aborts (either via an explicit
+the current look-ahead when the parser aborts (either via an explicit
 call to @code{YYABORT}, or as a consequence of a failed error recovery).
 @end itemize
 
@@ -5579,11 +5590,10 @@ constant integer.  The default is 200.
 
 @c FIXME: C++ output.
 Because of semantical differences between C and C++, the
-@acronym{LALR}(1) parsers
+@acronym{LALR}(1) parsers in C produced by Bison by compiled as C++
-in C produced by Bison by compiled as C++ cannot grow.  In this precise
+cannot grow.  In this precise case (compiling a C parser as C++) you are
-case (compiling a C parser as C++) you are suggested to grow
+suggested to grow @code{YYINITDEPTH}.  In the near future, a C++ output
-@code{YYINITDEPTH}.  In the near future, a C++ output output will be
+output will be provided which addresses this issue.
-provided which addresses this issue.
 
 @node Error Recovery
 @chapter Error Recovery
@@ -6887,19 +6897,18 @@ $ @kbd{printf 'one\ntwo\n' | ./split-lines}
 How can I generate parsers in C++?
 @end display
 
-We are working on a C++ output for Bison, but unfortunately, for lack
+We are working on a C++ output for Bison, but unfortunately, for lack of
-of time, the skeleton is not finished.  It is functional, but in
+time, the skeleton is not finished.  It is functional, but in numerous
-numerous respects, it will require additional work which @emph{might}
+respects, it will require additional work which @emph{might} break
-break backward compatibility.  Since the skeleton for C++ is not
+backward compatibility.  Since the skeleton for C++ is not documented,
-documented, we do not consider ourselves bound to this interface,
+we do not consider ourselves bound to this interface, nevertheless, as
-nevertheless, as much as possible we will try to keep compatibility.
+much as possible we will try to keep compatibility.
 
-Another possibility is to use the regular C parsers, and to compile
+Another possibility is to use the regular C parsers, and to compile them
-them with a C++ compiler.  This works properly, provided that you bear
+with a C++ compiler.  This works properly, provided that you bear some
-some simple C++ rules in mind, such as not including ``real classes''
+simple C++ rules in mind, such as not including ``real classes'' (i.e.,
-(i.e., structure with constructors) in unions.  Therefore, in the
+structure with constructors) in unions.  Therefore, in the
-@code{%union}, use pointers to classes, or better yet, a single
+@code{%union}, use pointers to classes.
-pointer type to the root of your lexical/syntactic hierarchy.
 
 
 @node Implementing Gotos/Loops

tests/actions.at

@@ -327,7 +327,7 @@ static bool yydebug;
 int
 yyparse ()
 {
-  yy::Parser parser (yydebug, yy::Location ());
+  yy::Parser parser (yydebug);
   return parser.parse ();
 }
 ],

tests/calc.at

@@ -144,7 +144,7 @@ yy::Parser::error_ ()
 int
 yyparse (AT_PARAM_IF([semantic_value *result, int *count]))
 {
-  yy::Parser parser (!!YYDEBUG[]AT_LOCATION_IF([, yy::Location ()])AT_PARAM_IF([, result, count]));
+  yy::Parser parser (!!YYDEBUG[]AT_PARAM_IF([, result, count]));
   return parser.parse ();
 }
 ],