c++: clean up the handling of empty symbols

[bison.git] / data / lalr1.cc

# C++ skeleton for Bison

# Copyright (C) 2002-2015 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])

# api.value.type=variant is valid.
m4_define([b4_value_type_setup_variant])

# b4_integral_parser_table_declare(TABLE-NAME, CONTENT, COMMENT)
# --------------------------------------------------------------
# Declare "parser::yy<TABLE-NAME>_" whose contents is CONTENT.
m4_define([b4_integral_parser_table_declare],
[m4_ifval([$3], [b4_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>_" whose 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.  Note that b4_value_type_setup_union
# overrides b4_symbol_value, so we must override it again.
m4_copy([b4_symbol_value], [b4_symbol_value_template])
m4_append([b4_value_type_setup_union],
          [m4_copy_force([b4_symbol_value_union], [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
])])


# b4_lex
# ------
# Call yylex.
m4_define([b4_lex],
[b4_token_ctor_if(
[b4_function_call([yylex],
                  [symbol_type], m4_ifdef([b4_lex_param], b4_lex_param))],
[b4_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))])])


m4_pushdef([b4_copyright_years],
           [2002-2015])

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

b4_bison_locations_if([# 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 <vector>
# include <iostream>
# include <stdexcept>
# include <string>]b4_defines_if([[
# include "stack.hh"
]b4_bison_locations_if([[# include "location.hh"]])])[
]b4_variant_if([b4_variant_includes])[

]b4_attribute_define[
]b4_YYDEBUG_define[

]b4_namespace_open[

]b4_defines_if([],
[b4_stack_define
b4_bison_locations_if([b4_position_define
b4_location_define])])[

]b4_variant_if([b4_variant_define])[

  /// 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 YY_ATTRIBUTE_PURE;
    /// 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 YY_ATTRIBUTE_PURE;
    /// 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:
    /// This class is not copyable.
    ]b4_parser_class_name[ (const ]b4_parser_class_name[&);
    ]b4_parser_class_name[& operator= (const ]b4_parser_class_name[&);

    /// State numbers.
    typedef int state_type;

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

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

    /// 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);

    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_;

    /// Convert a scanner token number \a t to a symbol number.
    static token_number_type yytranslate_ (]b4_token_ctor_if([token_type], [int])[ t);

    // 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_;

    /// \brief Display a symbol type, value and location.
    /// \param yyo    The output stream.
    /// \param yysym  The symbol.
    template <typename Base>
    void yy_print_ (std::ostream& yyo, const basic_symbol<Base>& yysym) const;
#endif

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

  private:
    /// Type access provider for state based symbols.
    struct by_state
    {
      /// Default constructor.
      by_state ();

      /// The symbol type as needed by the constructor.
      typedef state_type kind_type;

      /// Constructor.
      by_state (kind_type s);

      /// Copy constructor.
      by_state (const by_state& other);

      /// Steal the symbol type from \a that.
      void move (by_state& that);

      /// The (internal) type number (corresponding to \a state).
      /// \a empty_symbol when empty.
      symbol_number_type type_get () const;

      /// The state number used to denote an empty symbol.
      enum { empty_state = -1 };

      /// The state.
      /// \a empty when empty.
      state_type state;
    };

    /// "Internal" symbol: element of the stack.
    struct stack_symbol_type : basic_symbol<by_state>
    {
      /// Superclass.
      typedef basic_symbol<by_state> super_type;
      /// Construct an empty symbol.
      stack_symbol_type ();
      /// Steal the contents from \a sym to build this.
      stack_symbol_type (state_type s, symbol_type& sym);
      /// Assignment, needed by push_back.
      stack_symbol_type& operator= (const stack_symbol_type& that);
    };

    /// 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.
    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.
    void yypush_ (const char* m, state_type s, symbol_type& sym);

    /// Pop \a n symbols the three stacks.
    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.
      yyfinal_ = ]b4_final_state_number[, ///< Termination state number.
      yyterror_ = 1,
      yyerrcode_ = 256,
      yyntokens_ = ]b4_tokens_number[  ///< Number of tokens.
    };

]b4_parse_param_vars[
  };

]b4_token_ctor_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]])[
]])

b4_defines_if(
[b4_output_begin([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])
b4_output_end()
])


b4_output_begin([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[

]b4_defines_if([[#include "@basename(]b4_spec_defines_file[@)"]],
               [b4_shared_declarations])[

// 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_token_ctor_if([], [b4_public_types_define])[

  // by_state.
  inline
  ]b4_parser_class_name[::by_state::by_state ()
    : state (empty_state)
  {}

  inline
  ]b4_parser_class_name[::by_state::by_state (const by_state& other)
    : state (other.state)
  {}

  inline
  void
  ]b4_parser_class_name[::by_state::move (by_state& that)
  {
    state = that.state;
    that.state = empty_state;
  }

  inline
  ]b4_parser_class_name[::by_state::by_state (state_type s)
    : state (s)
  {}

  inline
  ]b4_parser_class_name[::symbol_number_type
  ]b4_parser_class_name[::by_state::type_get () const
  {
    return state == empty_state ? empty_symbol : yystos_[state];
  }

  inline
  ]b4_parser_class_name[::stack_symbol_type::stack_symbol_type ()
  {}


  inline
  ]b4_parser_class_name[::stack_symbol_type::stack_symbol_type (state_type s, symbol_type& that)
    : super_type (s]b4_locations_if([, that.location])[)
  {
    ]b4_variant_if([b4_symbol_variant([that.type_get ()],
                                      [value], [move], [that.value])],
                   [[value = that.value;]])[
    // that is emptied.
    that.type = empty_symbol;
  }

  inline
  ]b4_parser_class_name[::stack_symbol_type&
  ]b4_parser_class_name[::stack_symbol_type::operator= (const stack_symbol_type& that)
  {
    state = that.state;
    ]b4_variant_if([b4_symbol_variant([that.type_get ()],
                                      [value], [copy], [that.value])],
                   [[value = that.value;]])[]b4_locations_if([
    location = that.location;])[
    return *this;
  }


  template <typename Base>
  inline
  void
  ]b4_parser_class_name[::yy_destroy_ (const char* yymsg, basic_symbol<Base>& yysym) const
  {
    if (yymsg)
      YY_SYMBOL_PRINT (yymsg, yysym);]b4_variant_if([], [

    // User destructor.
    b4_symbol_actions([destructor], [yysym.type_get ()])])[
  }

#if ]b4_api_PREFIX[DEBUG
  template <typename Base>
  void
  ]b4_parser_class_name[::yy_print_ (std::ostream& yyo,
                                     const basic_symbol<Base>& yysym) const
  {
    std::ostream& yyoutput = yyo;
    YYUSE (yyoutput);
    symbol_number_type yytype = yysym.type_get ();
    yyo << (yytype < yyntokens_ ? "token" : "nterm")
        << ' ' << yytname_[yytype] << " ("]b4_locations_if([
        << yysym.location << ": "])[;
    ]b4_symbol_actions([printer])[
    yyo << ')';
  }
#endif

  inline
  void
  ]b4_parser_class_name[::yypush_ (const char* m, state_type s, symbol_type& sym)
  {
    stack_symbol_type t (s, sym);
    yypush_ (m, t);
  }

  inline
  void
  ]b4_parser_class_name[::yypush_ (const char* m, stack_symbol_type& s)
  {
    if (m)
      YY_SYMBOL_PRINT (m, s);
    yystack_.push (s);
  }

  inline
  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 yysym)
  {
    int yyr = yypgoto_[yysym - yyntokens_] + yystate;
    if (0 <= yyr && yyr <= yylast_ && yycheck_[yyr] == yystate)
      return yytable_[yyr];
    else
      return yydefgoto_[yysym - 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 ()
  {
    // State.
    int yyn;
    /// Length of the RHS of the rule being reduced.
    int yylen = 0;

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

    /// Whether yyla contains a lookahead.
    bool yyempty = true;

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

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

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

    // FIXME: This shoud be completely indented.  It is not yet to
    // avoid gratuitous conflicts when merging into the master branch.
    try
      {
    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_.clear ();
    yypush_ (YY_NULLPTR, 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_token_ctor_if([[
            symbol_type yylookahead (]b4_lex[);
            yyla.move (yylookahead);]], [[
            yyla.type = yytranslate_ (]b4_lex[);]])[
          }
        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_get ();
    if (yyn < 0 || yylast_ < yyn || yycheck_[yyn] != yyla.type_get ())
      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];
    {
      stack_symbol_type yylhs;
      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);
      yypop_ (yylen);
      yylen = 0;
      YY_STACK_PRINT ();

      // Shift the result of the reduction.
      yypush_ (YY_NULLPTR, yylhs);
    }
    goto yynewstate;

  /*--------------------------------------.
  | yyerrlab -- here on detecting error.  |
  `--------------------------------------*/
  yyerrlab:
    // If not already recovering from an error, report this error.
    if (!yyerrstatus_)
      {
        ++yynerrs_;
        error (]b4_join(b4_locations_if([yyla.location]),
                        [[yysyntax_error_ (yystack_[0].state,
                                           yyempty ? empty_symbol : yyla.type_get ())]])[);
      }

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

    return yyresult;
  }
    catch (...)
      {
        YYCDEBUG << "Exception caught: cleaning lookahead and stack"
                 << std::endl;
        // Do not try to display the values of the reclaimed symbols,
        // as their printer might throw an exception.
        if (!yyempty)
          yy_destroy_ (YY_NULLPTR, yyla);

        while (1 < yystack_.size ())
          {
            yy_destroy_ (YY_NULLPTR, yystack_[0]);
            yypop_ ();
          }
        throw;
      }
  }

  void
  ]b4_parser_class_name[::error (const syntax_error& yyexc)
  {
    error (]b4_join(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, symbol_number_type yytoken],
                    [state_type, symbol_number_type])[) const
  {]b4_error_verbose_if([[
    // 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 != empty_symbol)
      {
        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_NULLPTR;
    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_
      }

    std::string yyres;
    // 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_token_ctor_if([], [b4_yytranslate_define])[
]b4_namespace_close[
]b4_epilogue[]dnl
b4_output_end()


m4_popdef([b4_copyright_years])dnl