skeletons: style changes

[bison.git] / data / lalr1.cc

# C++ skeleton for Bison

# Copyright (C) 2002-2012 Free Software Foundation, Inc.

# This program is free software: you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program.  If not, see <http://www.gnu.org/licenses/>.

m4_include(b4_pkgdatadir/[c++.m4])


# b4_integral_parser_table_declare(TABLE-NAME, CONTENT, COMMENT)
# --------------------------------------------------------------
# Declare "parser::yy<TABLE-NAME>_" which contents is CONTENT.
m4_define([b4_integral_parser_table_declare],
[m4_ifval([$3], [b4_c_comment([$3], [  ])
])dnl
  static const b4_int_type_for([$2]) yy$1_[[]];dnl
])

# b4_integral_parser_table_define(TABLE-NAME, CONTENT, COMMENT)
# -------------------------------------------------------------
# Define "parser::yy<TABLE-NAME>_" which contents is CONTENT.
m4_define([b4_integral_parser_table_define],
[  const b4_int_type_for([$2])
  b4_parser_class_name::yy$1_[[]] =
  {
  $2
  };dnl
])


# b4_symbol_value_template(VAL, [TYPE])
# -------------------------------------
# Same as b4_symbol_value, but used in a template method.  It makes
# a difference when using variants.
m4_copy([b4_symbol_value], [b4_symbol_value_template])


# b4_lhs_value([TYPE])
# --------------------
# Expansion of $<TYPE>$.
m4_define([b4_lhs_value],
          [b4_symbol_value([yylhs.value], [$1])])


# b4_lhs_location()
# -----------------
# Expansion of @$.
m4_define([b4_lhs_location],
          [yylhs.location])


# b4_rhs_data(RULE-LENGTH, NUM)
# -----------------------------
# Return the data corresponding to the symbol #NUM, where the current
# rule has RULE-LENGTH symbols on RHS.
m4_define([b4_rhs_data],
          [yystack_@{b4_subtract($@)@}])


# b4_rhs_state(RULE-LENGTH, NUM)
# ------------------------------
# The state corresponding to the symbol #NUM, where the current
# rule has RULE-LENGTH symbols on RHS.
m4_define([b4_rhs_state],
          [b4_rhs_data([$1], [$2]).state])


# b4_rhs_value(RULE-LENGTH, NUM, [TYPE])
# --------------------------------------
# Expansion of $<TYPE>NUM, where the current rule has RULE-LENGTH
# symbols on RHS.
m4_define([b4_rhs_value],
          [b4_symbol_value([b4_rhs_data([$1], [$2]).value], [$3])])


# b4_rhs_location(RULE-LENGTH, NUM)
# ---------------------------------
# Expansion of @NUM, where the current rule has RULE-LENGTH symbols
# on RHS.
m4_define([b4_rhs_location],
          [b4_rhs_data([$1], [$2]).location])


# b4_symbol_action(SYMBOL-NUM, KIND)
# ----------------------------------
# Run the action KIND (destructor or printer) for SYMBOL-NUM.
# Same as in C, but using references instead of pointers.
m4_define([b4_symbol_action],
[b4_symbol_if([$1], [has_$2],
[m4_pushdef([b4_symbol_value], m4_defn([b4_symbol_value_template]))[]dnl
b4_dollar_pushdef([yysym.value],
                   b4_symbol_if([$1], [has_type],
                                [m4_dquote(b4_symbol([$1], [type]))]),
                   [yysym.location])dnl
      b4_symbol_case_([$1])
b4_syncline([b4_symbol([$1], [$2_line])], ["b4_symbol([$1], [$2_file])"])
        b4_symbol([$1], [$2])
b4_syncline([@oline@], [@ofile@])
        break;

m4_popdef([b4_symbol_value])[]dnl
b4_dollar_popdef[]dnl
])])


m4_pushdef([b4_copyright_years],
           [2002-2012])

m4_define([b4_parser_class_name],
          [b4_percent_define_get([[parser_class_name]])])

# The header is mandatory.
b4_defines_if([],
              [b4_fatal([b4_skeleton[: using %%defines is mandatory]])])

b4_locations_if([b4_percent_define_ifdef([[location_type]], [],
  [# Backward compatibility.
   m4_define([b4_location_constructors])
   m4_include(b4_pkgdatadir/[location.cc])])])
m4_include(b4_pkgdatadir/[stack.hh])
b4_variant_if([m4_include(b4_pkgdatadir/[variant.hh])])

# b4_shared_declarations
# ----------------------
# Declaration that might either go into the header (if --defines)
# or open coded in the parser body.
m4_define([b4_shared_declarations],
[b4_percent_code_get([[requires]])[
]b4_parse_assert_if([# include <cassert>])[
# include <stdexcept>
# include <string>
# include <iostream>
# include "stack.hh"
]b4_locations_if([b4_percent_define_ifdef([[location_type]], [],
                                          [[# include "location.hh"]])])[

]b4_variant_if([b4_namespace_open
b4_variant_define
b4_namespace_close])[

]b4_YYDEBUG_define[

]b4_namespace_open[

  /// A Bison parser.
  class ]b4_parser_class_name[
  {
  public:
]b4_public_types_declare[
    /// Build a parser object.
    ]b4_parser_class_name[ (]b4_parse_param_decl[);
    virtual ~]b4_parser_class_name[ ();

    /// Parse.
    /// \returns  0 iff parsing succeeded.
    virtual int parse ();

#if ]b4_api_PREFIX[DEBUG
    /// The current debugging stream.
    std::ostream& debug_stream () const;
    /// Set the current debugging stream.
    void set_debug_stream (std::ostream &);

    /// Type for debugging levels.
    typedef int debug_level_type;
    /// The current debugging level.
    debug_level_type debug_level () const;
    /// Set the current debugging level.
    void set_debug_level (debug_level_type l);
#endif

    /// Report a syntax error.]b4_locations_if([[
    /// \param loc    where the syntax error is found.]])[
    /// \param msg    a description of the syntax error.
    virtual void error (]b4_locations_if([[const location_type& loc, ]])[const std::string& msg);

    /// Report a syntax error.
    void error (const syntax_error& err);

  private:
    /// State numbers.
    typedef int state_type;

    /// Generate an error message.
    /// \param yystate   the state where the error occurred.
    /// \param yytoken   the lookahead token.
    virtual std::string yysyntax_error_ (state_type yystate, int yytoken);

    /// Compute post-reduction state.
    /// \param yystate   the current state
    /// \param yylhs     the nonterminal to push on the stack
    state_type yy_lr_goto_state_ (state_type yystate, int yylhs);

    /// Whether the given \c yypact_ value indicates a defaulted state.
    /// \param yyvalue   the value to check
    static bool yy_pact_value_is_default_ (int yyvalue);

    /// Whether the given \c yytable_ value indicates a syntax error.
    /// \param yyvalue   the value to check
    static bool yy_table_value_is_error_ (int yyvalue);

    /// Internal symbol numbers.
    typedef ]b4_int_type_for([b4_translate])[ token_number_type;
    static const ]b4_int_type(b4_pact_ninf, b4_pact_ninf)[ yypact_ninf_;
    static const ]b4_int_type(b4_table_ninf, b4_table_ninf)[ yytable_ninf_;

    // Tables.
]b4_parser_tables_declare[]b4_error_verbose_if([

    /// Convert the symbol name \a n to a form suitable for a diagnostic.
    static std::string yytnamerr_ (const char *n);])[

]b4_token_table_if([], [[#if ]b4_api_PREFIX[DEBUG]])[
    /// For a symbol, its name in clear.
    static const char* const yytname_[];
]b4_token_table_if([[#if ]b4_api_PREFIX[DEBUG]])[
]b4_integral_parser_table_declare([rline], [b4_rline],
     [YYRLINE[YYN] -- Source line where rule number YYN was defined.])[
    /// Report on the debug stream that the rule \a r is going to be reduced.
    virtual void yy_reduce_print_ (int r);
    /// Print the state stack on the debug stream.
    virtual void yystack_print_ ();

    // Debugging.
    int yydebug_;
    std::ostream* yycdebug_;
#endif // ]b4_api_PREFIX[DEBUG

    /// Convert a scanner token number \a t to a symbol number.
    static inline token_number_type yytranslate_ (]b4_lex_symbol_if([token_type], [int])[ t);

#if ]b4_api_PREFIX[DEBUG
    /// \brief Display a symbol type, value and location.
    /// \param yyo    The output stream.
    /// \param yysym  The symbol.
    template <typename Exact>
    void yy_print_ (std::ostream& yyo,
                    const symbol_base_type<Exact>& yysym) const;
#endif

    /// \brief Reclaim the memory associated to a symbol.
    /// \param yymsg     Why this token is reclaimed.
    ///                  If null, print nothing.
    /// \param s         The symbol.
    template <typename Exact>
    inline void yy_destroy_ (const char* yymsg,
                             symbol_base_type<Exact>& yysym) const;

  private:
    /// Element of the stack: a state and its attributes.
    struct stack_symbol_type : symbol_base_type<stack_symbol_type>
    {
      /// The parent class.
      typedef symbol_base_type<stack_symbol_type> super_type;

      /// Default constructor.
      inline stack_symbol_type ();

      /// Constructor.
      inline stack_symbol_type (]b4_args([state_type s],
                                         [const semantic_type& v],
                                         b4_locations_if([const location_type& l]))[);

      /// The state.
      state_type state;

      /// The type (corresponding to \a state).
      inline int type_get_ () const;
    };

    /// Stack type.
    typedef stack<stack_symbol_type> stack_type;

    /// The stack.
    stack_type yystack_;

    /// Push a new state on the stack.
    /// \param m    a debug message to display
    ///             if null, no trace is output.
    /// \param s    the symbol
    /// \warning the contents of \a s.value is stolen.
    inline void yypush_ (const char* m, stack_symbol_type& s);

    /// Push a new look ahead token on the state on the stack.
    /// \param m    a debug message to display
    ///             if null, no trace is output.
    /// \param s    the state
    /// \param sym  the symbol (for its value and location).
    /// \warning the contents of \a s.value is stolen.
    inline void yypush_ (const char* m, state_type s, symbol_type& sym);

    /// Pop \a n symbols the three stacks.
    inline void yypop_ (unsigned int n = 1);

    /* Constants.  */
    enum
    {
      yyeof_ = 0,
      yylast_ = ]b4_last[,           //< Last index in yytable_.
      yynnts_ = ]b4_nterms_number[,  //< Number of nonterminal symbols.
      yyempty_ = -2,
      yyfinal_ = ]b4_final_state_number[, //< Termination state number.
      yyterror_ = 1,
      yyerrcode_ = 256,
      yyntokens_ = ]b4_tokens_number[    //< Number of tokens.
    };

]b4_parse_param_vars[
  };

]b4_lex_symbol_if([b4_yytranslate_define
b4_public_types_define])[
]b4_namespace_close[

]b4_percent_define_flag_if([[global_tokens_and_yystype]],
[b4_token_defines

#ifndef ]b4_api_PREFIX[STYPE
 /* Redirection for backward compatibility.  */
# define ]b4_api_PREFIX[STYPE b4_namespace_ref::b4_parser_class_name::semantic_type
#endif
])[
]b4_percent_code_get([[provides]])[
]])

# We do want M4 expansion after # for CPP macros.
m4_changecom()
m4_divert_push(0)dnl
@output(b4_spec_defines_file@)@
b4_copyright([Skeleton interface for Bison LALR(1) parsers in C++])
[
/**
 ** \file ]b4_spec_defines_file[
 ** Define the ]b4_namespace_ref[::parser class.
 */

/* C++ LALR(1) parser skeleton written by Akim Demaille.  */

]b4_cpp_guard_open([b4_spec_defines_file])[
]b4_shared_declarations[
]b4_cpp_guard_close([b4_spec_defines_file])
@output(b4_parser_file_name@)@
b4_copyright([Skeleton implementation for Bison LALR(1) parsers in C++])
b4_percent_code_get([[top]])[]dnl
m4_if(b4_prefix, [yy], [],
[
// Take the name prefix into account.
#define yylex   b4_prefix[]lex])[

// First part of user declarations.
]b4_user_pre_prologue[

]b4_null_define[

#include "@basename(]b4_spec_defines_file[@)"

/* User implementation prologue.  */
]b4_user_post_prologue[
]b4_percent_code_get[

#ifndef YY_
# if defined YYENABLE_NLS && YYENABLE_NLS
#  if ENABLE_NLS
#   include <libintl.h> /* FIXME: INFRINGES ON USER NAME SPACE */
#   define YY_(msgid) dgettext ("bison-runtime", msgid)
#  endif
# endif
# ifndef YY_
#  define YY_(msgid) msgid
# endif
#endif

]b4_locations_if([dnl
[#define YYRHSLOC(Rhs, K) ((Rhs)[K].location)
]b4_yylloc_default_define])[

/* Suppress unused-variable warnings by "using" E.  */
#define YYUSE(e) ((void) (e))

/* Enable debugging if requested.  */
#if ]b4_api_PREFIX[DEBUG

/* A pseudo ostream that takes yydebug_ into account.  */
# define YYCDEBUG if (yydebug_) (*yycdebug_)

# define YY_SYMBOL_PRINT(Title, Symbol)         \
  do {                                          \
    if (yydebug_)                               \
    {                                           \
      *yycdebug_ << Title << ' ';               \
      yy_print_ (*yycdebug_, Symbol);           \
      *yycdebug_ << std::endl;                  \
    }                                           \
  } while (false)

# define YY_REDUCE_PRINT(Rule)          \
  do {                                  \
    if (yydebug_)                       \
      yy_reduce_print_ (Rule);          \
  } while (false)

# define YY_STACK_PRINT()               \
  do {                                  \
    if (yydebug_)                       \
      yystack_print_ ();                \
  } while (false)

#else /* !]b4_api_PREFIX[DEBUG */

# define YYCDEBUG if (false) std::cerr
# define YY_SYMBOL_PRINT(Title, Symbol)  YYUSE(Symbol)
# define YY_REDUCE_PRINT(Rule)           static_cast<void>(0)
# define YY_STACK_PRINT()                static_cast<void>(0)

#endif /* !]b4_api_PREFIX[DEBUG */

#define yyerrok         (yyerrstatus_ = 0)
#define yyclearin       (yyempty = true)

#define YYACCEPT        goto yyacceptlab
#define YYABORT         goto yyabortlab
#define YYERROR         goto yyerrorlab
#define YYRECOVERING()  (!!yyerrstatus_)

]b4_namespace_open[]b4_error_verbose_if([[

  /* Return YYSTR after stripping away unnecessary quotes and
     backslashes, so that it's suitable for yyerror.  The heuristic is
     that double-quoting is unnecessary unless the string contains an
     apostrophe, a comma, or backslash (other than backslash-backslash).
     YYSTR is taken from yytname.  */
  std::string
  ]b4_parser_class_name[::yytnamerr_ (const char *yystr)
  {
    if (*yystr == '"')
      {
        std::string yyr = "";
        char const *yyp = yystr;

        for (;;)
          switch (*++yyp)
            {
            case '\'':
            case ',':
              goto do_not_strip_quotes;

            case '\\':
              if (*++yyp != '\\')
                goto do_not_strip_quotes;
              /* Fall through.  */
            default:
              yyr += *yyp;
              break;

            case '"':
              return yyr;
            }
      do_not_strip_quotes: ;
      }

    return yystr;
  }
]])[

  /// Build a parser object.
  ]b4_parser_class_name::b4_parser_class_name[ (]b4_parse_param_decl[)]m4_ifset([b4_parse_param], [
    :])[
#if ]b4_api_PREFIX[DEBUG
    ]m4_ifset([b4_parse_param], [  ], [ :])[yydebug_ (false),
      yycdebug_ (&std::cerr)]m4_ifset([b4_parse_param], [,])[
#endif]b4_parse_param_cons[
  {
  }

  ]b4_parser_class_name::~b4_parser_class_name[ ()
  {
  }


  /*---------------.
  | Symbol types.  |
  `---------------*/

]b4_lex_symbol_if([], [b4_public_types_define])[

  // stack_symbol_type.
  ]b4_parser_class_name[::stack_symbol_type::stack_symbol_type ()
    : super_type ()
    , state ()
  {
  }

  ]b4_parser_class_name[::stack_symbol_type::stack_symbol_type (]b4_args(
                 [state_type s],
                 [const semantic_type& v],
                 b4_locations_if([const location_type& l]))[)
    : super_type (v]b4_locations_if([, l])[)
    , state (s)
  {
  }

  int
  ]b4_parser_class_name[::stack_symbol_type::type_get_ () const
  {
    return yystos_[state];
  }


  template <typename Exact>
  void
  ]b4_parser_class_name[::yy_destroy_ (const char* yymsg,
                                       symbol_base_type<Exact>& yysym) const
  {
    if (yymsg)
      YY_SYMBOL_PRINT (yymsg, yysym);

    // User destructor.
    int yytype = yysym.type_get ();
    switch (yytype)
      {
]b4_symbol_foreach([b4_symbol_destructor])dnl
[       default:
          break;
      }]b4_variant_if([

    // Type destructor.
  b4_symbol_variant([[yytype]], [[yysym.value]], [[template destroy]])])[
  }

#if ]b4_api_PREFIX[DEBUG
  template <typename Exact>
  void
  ]b4_parser_class_name[::yy_print_ (std::ostream& yyo,
                                     const symbol_base_type<Exact>& yysym) const
  {
    std::ostream& yyoutput = yyo;
    YYUSE (yyoutput);
    int yytype = yysym.type_get ();
    yyo << (yytype < yyntokens_ ? "token" : "nterm")
        << ' ' << yytname_[yytype] << " ("]b4_locations_if([
        << yysym.location << ": "])[;
    switch (yytype)
      {
]b4_symbol_foreach([b4_symbol_printer])dnl
[       default:
          break;
      }
    yyo << ')';
  }
#endif

  void
  ]b4_parser_class_name[::yypush_ (const char* m, state_type s,
                                   symbol_type& sym)
  {
    if (m)
      YY_SYMBOL_PRINT (m, sym);
]b4_variant_if(
[[    yystack_.push (stack_symbol_type (]b4_args(
                    [s],
                    [semantic_type()],
                    b4_locations_if([sym.location]))[));
    ]b4_symbol_variant([[yystos_[s]]], [[yystack_[0].value]],
                       [build], [sym.value])],
[[    yystack_.push (stack_symbol_type (]b4_args(
                      [s],
                      [sym.value],
                      b4_locations_if([sym.location]))[));]])[
  }

  void
  ]b4_parser_class_name[::yypush_ (const char* m, stack_symbol_type& s)
  {
    if (m)
      YY_SYMBOL_PRINT (m, s);
]b4_variant_if(
[[    yystack_.push (stack_symbol_type (]b4_args(
                       [s.state],
                       [semantic_type()],
                       b4_locations_if([s.location]))[));
    ]b4_symbol_variant([[yystos_[s.state]]], [[yystack_[0].value]],
                       [build], [s.value])],
[    yystack_.push (s);])[
  }

  void
  ]b4_parser_class_name[::yypop_ (unsigned int n)
  {
    yystack_.pop (n);
  }

#if ]b4_api_PREFIX[DEBUG
  std::ostream&
  ]b4_parser_class_name[::debug_stream () const
  {
    return *yycdebug_;
  }

  void
  ]b4_parser_class_name[::set_debug_stream (std::ostream& o)
  {
    yycdebug_ = &o;
  }


  ]b4_parser_class_name[::debug_level_type
  ]b4_parser_class_name[::debug_level () const
  {
    return yydebug_;
  }

  void
  ]b4_parser_class_name[::set_debug_level (debug_level_type l)
  {
    yydebug_ = l;
  }
#endif // ]b4_api_PREFIX[DEBUG

  inline ]b4_parser_class_name[::state_type
  ]b4_parser_class_name[::yy_lr_goto_state_ (state_type yystate, int yylhs)
  {
    int yyr = yypgoto_[yylhs - yyntokens_] + yystate;
    if (0 <= yyr && yyr <= yylast_ && yycheck_[yyr] == yystate)
      return yytable_[yyr];
    else
      return yydefgoto_[yylhs - yyntokens_];
  }

  inline bool
  ]b4_parser_class_name[::yy_pact_value_is_default_ (int yyvalue)
  {
    return yyvalue == yypact_ninf_;
  }

  inline bool
  ]b4_parser_class_name[::yy_table_value_is_error_ (int yyvalue)
  {
    return yyvalue == yytable_ninf_;
  }

  int
  ]b4_parser_class_name[::parse ()
  {
    /// Whether yyla contains a lookahead.
    bool yyempty = true;

    /* State.  */
    int yyn;
    int yylen = 0;

    /* Error handling.  */
    int yynerrs_ = 0;
    int yyerrstatus_ = 0;

    /// The lookahead symbol.
    symbol_type yyla;]b4_locations_if([[

    /// The locations where the error started and ended.
    stack_symbol_type yyerror_range[3];]])[

    /// $$ and @@$.
    stack_symbol_type yylhs;

    /// The return value of parse ().
    int yyresult;

    YYCDEBUG << "Starting parse" << std::endl;

]m4_ifdef([b4_initial_action], [
b4_dollar_pushdef([yyla.value], [], [yyla.location])dnl
    /* User initialization code.  */
    b4_user_initial_action
b4_dollar_popdef])[]dnl

  [  /* Initialize the stack.  The initial state will be set in
       yynewstate, since the latter expects the semantical and the
       location values to have been already stored, initialize these
       stacks with a primary value.  */
    yystack_ = stack_type (0);
    yypush_ (YY_NULL, 0, yyla);

    // A new symbol was pushed on the stack.
  yynewstate:
    YYCDEBUG << "Entering state " << yystack_[0].state << std::endl;

    /* Accept?  */
    if (yystack_[0].state == yyfinal_)
      goto yyacceptlab;

    goto yybackup;

    /* Backup.  */
  yybackup:

    /* Try to take a decision without lookahead.  */
    yyn = yypact_[yystack_[0].state];
    if (yy_pact_value_is_default_ (yyn))
      goto yydefault;

    /* Read a lookahead token.  */
    if (yyempty)
      {
        YYCDEBUG << "Reading a token: ";
        try
        {
]b4_lex_symbol_if(
[          yyla = b4_c_function_call([yylex], [symbol_type],
                                     m4_ifdef([b4_lex_param], b4_lex_param));],
[          yyla.type = yytranslate_ (b4_c_function_call([yylex], [int],
                                     [b4_api_PREFIX[STYPE*], [&yyla.value]][]dnl
b4_locations_if([, [[location*], [&yyla.location]]])dnl
m4_ifdef([b4_lex_param], [, ]b4_lex_param)));])[
        }
        catch (const syntax_error& yyexc)
        {
          error (yyexc);
          goto yyerrlab1;
        }
        yyempty = false;
      }
    YY_SYMBOL_PRINT ("Next token is", yyla);

    /* If the proper action on seeing token YYLA.TYPE is to reduce or
       to detect an error, take that action.  */
    yyn += yyla.type;
    if (yyn < 0 || yylast_ < yyn || yycheck_[yyn] != yyla.type)
      goto yydefault;

    /* Reduce or error.  */
    yyn = yytable_[yyn];
    if (yyn <= 0)
      {
        if (yy_table_value_is_error_ (yyn))
          goto yyerrlab;
        yyn = -yyn;
        goto yyreduce;
      }

    /* Discard the token being shifted.  */
    yyempty = true;

    /* Count tokens shifted since error; after three, turn off error
       status.  */
    if (yyerrstatus_)
      --yyerrstatus_;

    /* Shift the lookahead token.  */
    yypush_ ("Shifting", yyn, yyla);
    goto yynewstate;

  /*-----------------------------------------------------------.
  | yydefault -- do the default action for the current state.  |
  `-----------------------------------------------------------*/
  yydefault:
    yyn = yydefact_[yystack_[0].state];
    if (yyn == 0)
      goto yyerrlab;
    goto yyreduce;

  /*-----------------------------.
  | yyreduce -- Do a reduction.  |
  `-----------------------------*/
  yyreduce:
    yylen = yyr2_[yyn];
    yylhs.state = yy_lr_goto_state_(yystack_[yylen].state, yyr1_[yyn]);]b4_variant_if([
    /* Variants are always initialized to an empty instance of the
       correct type. The default $$=$1 action is NOT applied when using
       variants.  */
    b4_symbol_variant([[yyr1_@{yyn@}]], [yylhs.value], [build])],[
    /* If YYLEN is nonzero, implement the default value of the action:
       `$$ = $1'.  Otherwise, use the top of the stack.

       Otherwise, the following line sets YYLHS.VALUE to garbage.
       This behavior is undocumented and Bison
       users should not rely upon it.  */
    if (yylen)
      yylhs.value = yystack_@{yylen - 1@}.value;
    else
      yylhs.value = yystack_@{0@}.value;])[
]b4_locations_if([dnl
[
    // Compute the default @@$.
    {
      slice<stack_symbol_type, stack_type> slice (yystack_, yylen);
      YYLLOC_DEFAULT (yylhs.location, slice, yylen);
    }]])[

    // Perform the reduction.
    YY_REDUCE_PRINT (yyn);
    try
    {
      switch (yyn)
      {
]b4_user_actions[
        default:
          break;
      }
    }
    catch (const syntax_error& yyexc)
    {
      error (yyexc);
      YYERROR;
    }
    YY_SYMBOL_PRINT ("-> $$ =", yylhs);
]b4_variant_if([[
    // Destroy the rhs symbols.
    for (int i = 0; i < yylen; ++i)
      // Destroy a variant which value may have been swapped with
      // yylhs.value (for instance if the action was "std::swap($$,
      // $1)").  The value of yylhs.value (hence possibly one of these
      // rhs symbols) depends on the default construction for this
      // type.  In the case of pointers for instance, no
      // initialization is done, so the value is junk.  Therefore do
      // not try to report the value of symbols about to be destroyed
      // in the debug trace, it's possibly junk.  Hence yymsg = 0.
      // Besides, that keeps exactly the same traces as with the other
      // Bison skeletons.
      yy_destroy_ (YY_NULL, yystack_[i]);]])[

    yypop_ (yylen);
    yylen = 0;
    YY_STACK_PRINT ();

    /* Shift the result of the reduction.  */
    yypush_ (YY_NULL, yylhs);
    goto yynewstate;

  /*--------------------------------------.
  | yyerrlab -- here on detecting error.  |
  `--------------------------------------*/
  yyerrlab:
    /* If not already recovering from an error, report this error.  */
    if (!yyerrstatus_)
      {
        ++yynerrs_;
        error (]b4_args(b4_locations_if([yyla.location]),
                        [[yysyntax_error_ (yystack_[0].state,
                                           yyempty ? yyempty_ : yyla.type)]])[);
      }

]b4_locations_if([[
    yyerror_range[1].location = yyla.location;]])[
    if (yyerrstatus_ == 3)
      {
        /* If just tried and failed to reuse lookahead token after an
           error, discard it.  */

        /* Return failure if at end of input.  */
        if (yyla.type == yyeof_)
          YYABORT;
        else if (!yyempty)
          {
            yy_destroy_ ("Error: discarding", yyla);
            yyempty = true;
          }
      }

    /* Else will try to reuse lookahead token after shifting the error
       token.  */
    goto yyerrlab1;


  /*---------------------------------------------------.
  | yyerrorlab -- error raised explicitly by YYERROR.  |
  `---------------------------------------------------*/
  yyerrorlab:

    /* Pacify compilers like GCC when the user code never invokes
       YYERROR and the label yyerrorlab therefore never appears in user
       code.  */
    if (false)
      goto yyerrorlab;]b4_locations_if([[
    yyerror_range[1].location = yystack_[yylen - 1].location;]])b4_variant_if([[
    /* $$ was initialized before running the user action.  */
    yy_destroy_ ("Error: discarding", yylhs);]])[
    /* Do not reclaim the symbols of the rule which action triggered
       this YYERROR.  */
    yypop_ (yylen);
    yylen = 0;
    goto yyerrlab1;

  /*-------------------------------------------------------------.
  | yyerrlab1 -- common code for both syntax error and YYERROR.  |
  `-------------------------------------------------------------*/
  yyerrlab1:
    yyerrstatus_ = 3;   /* Each real token shifted decrements this.  */
    {
      stack_symbol_type error_token;
      for (;;)
        {
          yyn = yypact_[yystack_[0].state];
          if (!yy_pact_value_is_default_ (yyn))
            {
              yyn += yyterror_;
              if (0 <= yyn && yyn <= yylast_ && yycheck_[yyn] == yyterror_)
                {
                  yyn = yytable_[yyn];
                  if (0 < yyn)
                    break;
                }
            }

          // Pop the current state because it cannot handle the error token.
          if (yystack_.size () == 1)
            YYABORT;
]b4_locations_if([[
          yyerror_range[1].location = yystack_[0].location;]])[
          yy_destroy_ ("Error: popping", yystack_[0]);
          yypop_ ();
          YY_STACK_PRINT ();
        }
]b4_locations_if([[
      yyerror_range[2].location = yyla.location;
      YYLLOC_DEFAULT (error_token.location, yyerror_range, 2);]])[

      /* Shift the error token.  */
      error_token.state = yyn;
      yypush_ ("Shifting", error_token);
    }
    goto yynewstate;

    /* Accept.  */
  yyacceptlab:
    yyresult = 0;
    goto yyreturn;

    /* Abort.  */
  yyabortlab:
    yyresult = 1;
    goto yyreturn;

  yyreturn:
    if (!yyempty)
      yy_destroy_ ("Cleanup: discarding lookahead", yyla);

    /* Do not reclaim the symbols of the rule which action triggered
       this YYABORT or YYACCEPT.  */
    yypop_ (yylen);
    while (yystack_.size () != 1)
      {
        yy_destroy_ ("Cleanup: popping", yystack_[0]);
        yypop_ ();
      }

    return yyresult;
  }

  void
  ]b4_parser_class_name[::error (const syntax_error& yyexc)
  {
    error (]b4_args(b4_locations_if([yyexc.location]),
                    [[yyexc.what()]])[);
  }

  // Generate an error message.
  std::string
  ]b4_parser_class_name[::yysyntax_error_ (]dnl
b4_error_verbose_if([state_type yystate, int yytoken],
                    [int, int])[)
  {]b4_error_verbose_if([[
    std::string yyres;
    // Number of reported tokens (one for the "unexpected", one per
    // "expected").
    size_t yycount = 0;
    // Its maximum.
    enum { YYERROR_VERBOSE_ARGS_MAXIMUM = 5 };
    // Arguments of yyformat.
    char const *yyarg[YYERROR_VERBOSE_ARGS_MAXIMUM];

    /* There are many possibilities here to consider:
       - If this state is a consistent state with a default action, then
         the only way this function was invoked is if the default action
         is an error action.  In that case, don't check for expected
         tokens because there are none.
       - The only way there can be no lookahead present (in yytoken) is
         if this state is a consistent state with a default action.
         Thus, detecting the absence of a lookahead is sufficient to
         determine that there is no unexpected or expected token to
         report.  In that case, just report a simple "syntax error".
       - Don't assume there isn't a lookahead just because this state is
         a consistent state with a default action.  There might have
         been a previous inconsistent state, consistent state with a
         non-default action, or user semantic action that manipulated
         yyla.  (However, yyla is currently not documented for users.)
       - Of course, the expected token list depends on states to have
         correct lookahead information, and it depends on the parser not
         to perform extra reductions after fetching a lookahead from the
         scanner and before detecting a syntax error.  Thus, state
         merging (from LALR or IELR) and default reductions corrupt the
         expected token list.  However, the list is correct for
         canonical LR with one exception: it will still contain any
         token that will not be accepted due to an error action in a
         later state.
    */
    if (yytoken != yyempty_)
      {
        yyarg[yycount++] = yytname_[yytoken];
        int yyn = yypact_[yystate];
        if (!yy_pact_value_is_default_ (yyn))
          {
            /* Start YYX at -YYN if negative to avoid negative indexes in
               YYCHECK.  In other words, skip the first -YYN actions for
               this state because they are default actions.  */
            int yyxbegin = yyn < 0 ? -yyn : 0;
            /* Stay within bounds of both yycheck and yytname.  */
            int yychecklim = yylast_ - yyn + 1;
            int yyxend = yychecklim < yyntokens_ ? yychecklim : yyntokens_;
            for (int yyx = yyxbegin; yyx < yyxend; ++yyx)
              if (yycheck_[yyx + yyn] == yyx && yyx != yyterror_
                  && !yy_table_value_is_error_ (yytable_[yyx + yyn]))
                {
                  if (yycount == YYERROR_VERBOSE_ARGS_MAXIMUM)
                    {
                      yycount = 1;
                      break;
                    }
                  else
                    yyarg[yycount++] = yytname_[yyx];
                }
          }
      }

    char const* yyformat = YY_NULL;
    switch (yycount)
      {
#define YYCASE_(N, S)                         \
        case N:                               \
          yyformat = S;                       \
        break
        YYCASE_(0, YY_("syntax error"));
        YYCASE_(1, YY_("syntax error, unexpected %s"));
        YYCASE_(2, YY_("syntax error, unexpected %s, expecting %s"));
        YYCASE_(3, YY_("syntax error, unexpected %s, expecting %s or %s"));
        YYCASE_(4, YY_("syntax error, unexpected %s, expecting %s or %s or %s"));
        YYCASE_(5, YY_("syntax error, unexpected %s, expecting %s or %s or %s or %s"));
#undef YYCASE_
      }

    // Argument number.
    size_t yyi = 0;
    for (char const* yyp = yyformat; *yyp; ++yyp)
      if (yyp[0] == '%' && yyp[1] == 's' && yyi < yycount)
        {
          yyres += yytnamerr_ (yyarg[yyi++]);
          ++yyp;
        }
      else
        yyres += *yyp;
    return yyres;]], [[
    return YY_("syntax error");]])[
  }


  const ]b4_int_type(b4_pact_ninf, b4_pact_ninf) b4_parser_class_name::yypact_ninf_ = b4_pact_ninf[;

  const ]b4_int_type(b4_table_ninf, b4_table_ninf) b4_parser_class_name::yytable_ninf_ = b4_table_ninf[;

]b4_parser_tables_define[

]b4_token_table_if([], [[#if ]b4_api_PREFIX[DEBUG]])[
  /* YYTNAME[SYMBOL-NUM] -- String name of the symbol SYMBOL-NUM.
     First, the terminals, then, starting at \a yyntokens_, nonterminals.  */
  const char*
  const ]b4_parser_class_name[::yytname_[] =
  {
  ]b4_tname[
  };

]b4_token_table_if([[#if ]b4_api_PREFIX[DEBUG]])[
]b4_integral_parser_table_define([rline], [b4_rline])[

  // Print the state stack on the debug stream.
  void
  ]b4_parser_class_name[::yystack_print_ ()
  {
    *yycdebug_ << "Stack now";
    for (stack_type::const_iterator
           i = yystack_.begin (),
           i_end = yystack_.end ();
         i != i_end; ++i)
      *yycdebug_ << ' ' << i->state;
    *yycdebug_ << std::endl;
  }

  // Report on the debug stream that the rule \a yyrule is going to be reduced.
  void
  ]b4_parser_class_name[::yy_reduce_print_ (int yyrule)
  {
    unsigned int yylno = yyrline_[yyrule];
    int yynrhs = yyr2_[yyrule];
    /* Print the symbols being reduced, and their result.  */
    *yycdebug_ << "Reducing stack by rule " << yyrule - 1
               << " (line " << yylno << "):" << std::endl;
    /* The symbols being reduced.  */
    for (int yyi = 0; yyi < yynrhs; yyi++)
      YY_SYMBOL_PRINT ("   $" << yyi + 1 << " =",
                       ]b4_rhs_data(yynrhs, yyi + 1)[);
  }
#endif // ]b4_api_PREFIX[DEBUG

]b4_lex_symbol_if([], [b4_yytranslate_define])[
]b4_namespace_close[
]b4_epilogue[]dnl
m4_divert_pop(0)
m4_popdef([b4_copyright_years])dnl