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   *  This file is part of AndroidIDE.
   *
   *  AndroidIDE 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.
   *
   *  AndroidIDE 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 AndroidIDE.  If not, see <https://www.gnu.org/licenses/>.
   */
  
  /*
   * Copyright (c) 2003, 2005, Oracle and/or its affiliates. All rights reserved.
   * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   *
   * This code is free software; you can redistribute it and/or modify it
   * under the terms of the GNU General Public License version 2 only, as
   * published by the Free Software Foundation.  Oracle designates this
   * particular file as subject to the "Classpath" exception as provided
   * by Oracle in the LICENSE file that accompanied this code.
   *
   * This code 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
   * version 2 for more details (a copy is included in the LICENSE file that
   * accompanied this code).
   *
   * You should have received a copy of the GNU General Public License version
   * 2 along with this work; if not, write to the Free Software Foundation,
   * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
   *
   * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
   * or visit www.oracle.com if you need additional information or have any
   * questions.
   */
  
  
  package jaxp.sun.java_cup.internal.runtime;
  
  import java.util.Stack;
  
  /** This class implements a skeleton table driven LR parser.  In general,
   *  LR parsers are a form of bottom up shift-reduce parsers.  Shift-reduce
   *  parsers act by shifting input onto a parse stack until the Symbols
   *  matching the right hand side of a production appear on the top of the
   *  stack.  Once this occurs, a reduce is performed.  This involves removing
   *  the Symbols corresponding to the right hand side of the production
   *  (the so called "handle") and replacing them with the non-terminal from
   *  the left hand side of the production.  <p>
   *
   *  To control the decision of whether to shift or reduce at any given point,
   *  the parser uses a state machine (the "viable prefix recognition machine"
   *  built by the parser generator).  The current state of the machine is placed
   *  on top of the parse stack (stored as part of a Symbol object representing
   *  a terminal or non terminal).  The parse action table is consulted
   *  (using the current state and the current lookahead Symbol as indexes) to
   *  determine whether to shift or to reduce.  When the parser shifts, it
   *  changes to a new state by pushing a new Symbol (containing a new state)
   *  onto the stack.  When the parser reduces, it pops the handle (right hand
   *  side of a production) off the stack.  This leaves the parser in the state
   *  it was in before any of those Symbols were matched.  Next the reduce-goto
   *  table is consulted (using the new state and current lookahead Symbol as
   *  indexes) to determine a new state to go to.  The parser then shifts to
   *  this goto state by pushing the left hand side Symbol of the production
   *  (also containing the new state) onto the stack.<p>
   *
   *  This class actually provides four LR parsers.  The methods parse() and
   *  debug_parse() provide two versions of the main parser (the only difference
   *  being that debug_parse() emits debugging trace messages as it parses).
   *  In addition to these main parsers, the error recovery mechanism uses two
   *  more.  One of these is used to simulate "parsing ahead" in the input
   *  without carrying out actions (to verify that a potential error recovery
   *  has worked), and the other is used to parse through buffered "parse ahead"
   *  input in order to execute all actions and re-synchronize the actual parser
   *  configuration.<p>
   *
   *  This is an abstract class which is normally filled out by a subclass
   *  generated by the JavaCup parser generator.  In addition to supplying
   *  the actual parse tables, generated code also supplies methods which
   *  invoke various pieces of user supplied code, provide access to certain
   *  special Symbols (e.g., EOF and error), etc.  Specifically, the following
   *  abstract methods are normally supplied by generated code:
   *  <dl compact>
   *  <dt> short[][] production_table()
   *  <dd> Provides a reference to the production table (indicating the index of
   *       the left hand side non terminal and the length of the right hand side
   *       for each production in the grammar).
   *  <dt> short[][] action_table()
   *  <dd> Provides a reference to the parse action table.
   *  <dt> short[][] reduce_table()
   *  <dd> Provides a reference to the reduce-goto table.
   *  <dt> int start_state()
   *  <dd> Indicates the index of the start state.
   *  <dt> int start_production()
   *  <dd> Indicates the index of the starting production.
   *  <dt> int EOF_sym()
   *  <dd> Indicates the index of the EOF Symbol.
   *  <dt> int error_sym()
   *  <dd> Indicates the index of the error Symbol.
   *  <dt> Symbol do_action()
   *  <dd> Executes a piece of user supplied action code.  This always comes at
   *       the point of a reduce in the parse, so this code also allocates and
   *       fills in the left hand side non terminal Symbol object that is to be
   *       pushed onto the stack for the reduce.
   *  <dt> void init_actions()
   *  <dd> Code to initialize a special object that encapsulates user supplied
   *       actions (this object is used by do_action() to actually carry out the
   *       actions).
   *  </dl>
   *
   *  In addition to these routines that <i>must</i> be supplied by the
   *  generated subclass there are also a series of routines that <i>may</i>
   *  be supplied.  These include:
   *  <dl>
   *  <dt> Symbol scan()
   *  <dd> Used to get the next input Symbol from the scanner.
   *  <dt> Scanner getScanner()
   *  <dd> Used to provide a scanner for the default implementation of
   *       scan().
   *  <dt> int error_sync_size()
   *  <dd> This determines how many Symbols past the point of an error
   *       must be parsed without error in order to consider a recovery to
   *       be valid.  This defaults to 3.  Values less than 2 are not
   *       recommended.
   *  <dt> void report_error(String message, Object info)
   *  <dd> This method is called to report an error.  The default implementation
   *       simply prints a message to System.err and where the error occurred.
   *       This method is often replaced in order to provide a more sophisticated
   *       error reporting mechanism.
   *  <dt> void report_fatal_error(String message, Object info)
   *  <dd> This method is called when a fatal error that cannot be recovered from
   *       is encountered.  In the default implementation, it calls
   *       report_error() to emit a message, then throws an exception.
   *  <dt> void syntax_error(Symbol cur_token)
   *  <dd> This method is called as soon as syntax error is detected (but
   *       before recovery is attempted).  In the default implementation it
   *       invokes: report_error("Syntax error", null);
   *  <dt> void unrecovered_syntax_error(Symbol cur_token)
   *  <dd> This method is called if syntax error recovery fails.  In the default
   *       implementation it invokes:<br>
   *         report_fatal_error("Couldn't repair and continue parse", null);
   *  </dl>
   *
   * @see     Symbol
   * @see     Symbol
   * @see     virtual_parse_stack
   * @author  Frank Flannery
   */
  
  public abstract class lr_parser {
  
    /*-----------------------------------------------------------*/
    /*--- Constructor(s) ----------------------------------------*/
    /*-----------------------------------------------------------*/
  
    /** Simple constructor. */
    public lr_parser()
      {
        /* nothing to do here */
      }
  
    /** Constructor that sets the default scanner. [CSA/davidm] */
    public lr_parser(Scanner s) {
      this(); /* in case default constructor someday does something */
      setScanner(s);
    }
  
    /*-----------------------------------------------------------*/
    /*--- (Access to) Static (Class) Variables ------------------*/
    /*-----------------------------------------------------------*/
  
    /** The default number of Symbols after an error we much match to consider
     *  it recovered from.
     */
    protected final static int _error_sync_size = 3;
  
    /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
  
    /** The number of Symbols after an error we much match to consider it
     *  recovered from.
     */
    protected int error_sync_size() {return _error_sync_size; }
  
    /*-----------------------------------------------------------*/
    /*--- (Access to) Instance Variables ------------------------*/
    /*-----------------------------------------------------------*/
  
    /** Table of production information (supplied by generated subclass).
     *  This table contains one entry per production and is indexed by
     *  the negative-encoded values (reduce actions) in the action_table.
     *  Each entry has two parts, the index of the non-terminal on the
     *  left hand side of the production, and the number of Symbols
     *  on the right hand side.
     */
    public abstract short[][] production_table();
  
    /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
  
    /** The action table (supplied by generated subclass).  This table is
     *  indexed by state and terminal number indicating what action is to
     *  be taken when the parser is in the given state (i.e., the given state
     *  is on top of the stack) and the given terminal is next on the input.
     *  States are indexed using the first dimension, however, the entries for
     *  a given state are compacted and stored in adjacent index, value pairs
     *  which are searched for rather than accessed directly (see get_action()).
     *  The actions stored in the table will be either shifts, reduces, or
     *  errors.  Shifts are encoded as positive values (one greater than the
     *  state shifted to).  Reduces are encoded as negative values (one less
     *  than the production reduced by).  Error entries are denoted by zero.
     *
     * @see lr_parser#get_action
     */
    public abstract short[][] action_table();
  
    /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
  
    /** The reduce-goto table (supplied by generated subclass).  This
     *  table is indexed by state and non-terminal number and contains
     *  state numbers.  States are indexed using the first dimension, however,
     *  the entries for a given state are compacted and stored in adjacent
     *  index, value pairs which are searched for rather than accessed
     *  directly (see get_reduce()).  When a reduce occurs, the handle
     *  (corresponding to the RHS of the matched production) is popped off
     *  the stack.  The new top of stack indicates a state.  This table is
     *  then indexed by that state and the LHS of the reducing production to
     *  indicate where to "shift" to.
     *
     * @see lr_parser#get_reduce
     */
    public abstract short[][] reduce_table();
  
    /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
  
    /** The index of the start state (supplied by generated subclass). */
    public abstract int start_state();
  
    /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
  
    /** The index of the start production (supplied by generated subclass). */
    public abstract int start_production();
  
    /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
  
    /** The index of the end of file terminal Symbol (supplied by generated
     *  subclass).
     */
    public abstract int EOF_sym();
  
    /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
  
    /** The index of the special error Symbol (supplied by generated subclass). */
    public abstract int error_sym();
  
    /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
  
    /** Internal flag to indicate when parser should quit. */
    protected boolean _done_parsing = false;
  
    /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
  
    /** This method is called to indicate that the parser should quit.  This is
     *  normally called by an accept action, but can be used to cancel parsing
     *  early in other circumstances if desired.
     */
    public void done_parsing()
      {
        _done_parsing = true;
      }
  
    /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
    /* Global parse state shared by parse(), error recovery, and
     * debugging routines */
    /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
  
    /** Indication of the index for top of stack (for use by actions). */
    protected int tos;
  
    /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
  
    /** The current lookahead Symbol. */
    protected Symbol cur_token;
  
    /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
  
    /** The parse stack itself. */
    protected Stack stack = new Stack();
  
    /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
  
    /** Direct reference to the production table. */
    protected short[][] production_tab;
  
    /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
  
    /** Direct reference to the action table. */
    protected short[][] action_tab;
  
    /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
  
    /** Direct reference to the reduce-goto table. */
    protected short[][] reduce_tab;
  
    /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
  
    /** This is the scanner object used by the default implementation
     *  of scan() to get Symbols.  To avoid name conflicts with existing
     *  code, this field is private. [CSA/davidm] */
    private Scanner _scanner;
  
    /**
     * Simple accessor method to set the default scanner.
     */
    public void setScanner(Scanner s) { _scanner = s; }
  
    /**
     * Simple accessor method to get the default scanner.
     */
    public Scanner getScanner() { return _scanner; }
  
    /*-----------------------------------------------------------*/
    /*--- General Methods ---------------------------------------*/
    /*-----------------------------------------------------------*/
  
    /** Perform a bit of user supplied action code (supplied by generated
     *  subclass).  Actions are indexed by an internal action number assigned
     *  at parser generation time.
     *
     * @param act_num   the internal index of the action to be performed.
     * @param parser    the parser object we are acting for.
     * @param stack     the parse stack of that object.
     * @param top       the index of the top element of the parse stack.
     */
    public abstract Symbol do_action(
      int       act_num,
      lr_parser parser,
      Stack     stack,
      int       top)
      throws java.lang.Exception;
  
    /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
  
    /** User code for initialization inside the parser.  Typically this
     *  initializes the scanner.  This is called before the parser requests
     *  the first Symbol.  Here this is just a placeholder for subclasses that
     *  might need this and we perform no action.   This method is normally
     *  overridden by the generated code using this contents of the "init with"
     *  clause as its body.
     */
    public void user_init() throws java.lang.Exception { }
  
    /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
  
    /** Initialize the action object.  This is called before the parser does
     *  any parse actions. This is filled in by generated code to create
     *  an object that encapsulates all action code.
     */
    protected abstract void init_actions() throws java.lang.Exception;
  
    /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
  
    /** Get the next Symbol from the input (supplied by generated subclass).
     *  Once end of file has been reached, all subsequent calls to scan
     *  should return an EOF Symbol (which is Symbol number 0).  By default
     *  this method returns getScanner().next_token(); this implementation
     *  can be overriden by the generated parser using the code declared in
     *  the "scan with" clause.  Do not recycle objects; every call to
     *  scan() should return a fresh object.
     */
    public Symbol scan() throws java.lang.Exception {
      return getScanner().next_token();
    }
  
    /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
  
    /** Report a fatal error.  This method takes a  message string and an
     *  additional object (to be used by specializations implemented in
     *  subclasses).  Here in the base class a very simple implementation
     *  is provided which reports the error then throws an exception.
     *
     * @param message an error message.
     * @param info    an extra object reserved for use by specialized subclasses.
     */
    public void report_fatal_error(
      String   message,
      Object   info)
      throws java.lang.Exception
      {
        /* stop parsing (not really necessary since we throw an exception, but) */
        done_parsing();
  
        /* use the normal error message reporting to put out the message */
        report_error(message, info);
  
        /* throw an exception */
        throw new Exception("Can't recover from previous error(s)");
      }
  
    /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
  
    /** Report a non fatal error (or warning).  This method takes a message
     *  string and an additional object (to be used by specializations
     *  implemented in subclasses).  Here in the base class a very simple
     *  implementation is provided which simply prints the message to
     *  System.err.
     *
     * @param message an error message.
     * @param info    an extra object reserved for use by specialized subclasses.
     */
    public void report_error(String message, Object info)
      {
        System.err.print(message);
        if (info instanceof Symbol)
          if (((Symbol)info).left != -1)
          System.err.println(" at character " + ((Symbol)info).left +
                             " of input");
          else System.err.println("");
        else System.err.println("");
      }
  
    /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
  
    /** This method is called when a syntax error has been detected and recovery
     *  is about to be invoked.  Here in the base class we just emit a
     *  "Syntax error" error message.
     *
     * @param cur_token the current lookahead Symbol.
     */
    public void syntax_error(Symbol cur_token)
      {
        report_error("Syntax error", cur_token);
      }
  
    /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
  
    /** This method is called if it is determined that syntax error recovery
     *  has been unsuccessful.  Here in the base class we report a fatal error.
     *
     * @param cur_token the current lookahead Symbol.
     */
    public void unrecovered_syntax_error(Symbol cur_token)
      throws java.lang.Exception
      {
        report_fatal_error("Couldn't repair and continue parse", cur_token);
      }
  
    /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
  
    /** Fetch an action from the action table.  The table is broken up into
     *  rows, one per state (rows are indexed directly by state number).
     *  Within each row, a list of index, value pairs are given (as sequential
     *  entries in the table), and the list is terminated by a default entry
     *  (denoted with a Symbol index of -1).  To find the proper entry in a row
     *  we do a linear or binary search (depending on the size of the row).
     *
     * @param state the state index of the action being accessed.
     * @param sym   the Symbol index of the action being accessed.
     */
    protected final short get_action(int state, int sym)
      {
        short tag;
        int first, last, probe;
        short[] row = action_tab[state];
  
        /* linear search if we are < 10 entries */
        if (row.length < 20)
          for (probe = 0; probe < row.length; probe++)
            {
              /* is this entry labeled with our Symbol or the default? */
              tag = row[probe++];
              if (tag == sym || tag == -1)
                {
                  /* return the next entry */
                  return row[probe];
                }
            }
        /* otherwise binary search */
        else
          {
            first = 0;
            last = (row.length-1)/2 - 1;  /* leave out trailing default entry */
            while (first <= last)
              {
                probe = (first+last)/2;
                if (sym == row[probe*2])
                  return row[probe*2+1];
                else if (sym > row[probe*2])
                  first = probe+1;
                else
                  last = probe-1;
              }
  
            /* not found, use the default at the end */
            return row[row.length-1];
          }
  
        /* shouldn't happened, but if we run off the end we return the
           default (error == 0) */
        return 0;
      }
  
    /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
  
    /** Fetch a state from the reduce-goto table.  The table is broken up into
     *  rows, one per state (rows are indexed directly by state number).
     *  Within each row, a list of index, value pairs are given (as sequential
     *  entries in the table), and the list is terminated by a default entry
     *  (denoted with a Symbol index of -1).  To find the proper entry in a row
     *  we do a linear search.
     *
     * @param state the state index of the entry being accessed.
     * @param sym   the Symbol index of the entry being accessed.
     */
    protected final short get_reduce(int state, int sym)
      {
        short tag;
        short[] row = reduce_tab[state];
  
        /* if we have a null row we go with the default */
        if (row == null)
          return -1;
  
        for (int probe = 0; probe < row.length; probe++)
          {
            /* is this entry labeled with our Symbol or the default? */
            tag = row[probe++];
            if (tag == sym || tag == -1)
              {
                /* return the next entry */
                return row[probe];
              }
          }
        /* if we run off the end we return the default (error == -1) */
        return -1;
      }
  
    /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
  
    /** This method provides the main parsing routine.  It returns only when
     *  done_parsing() has been called (typically because the parser has
     *  accepted, or a fatal error has been reported).  See the header
     *  documentation for the class regarding how shift/reduce parsers operate
     *  and how the various tables are used.
     */
    public Symbol parse() throws java.lang.Exception
      {
        /* the current action code */
        int act;
  
        /* the Symbol/stack element returned by a reduce */
        Symbol lhs_sym = null;
  
        /* information about production being reduced with */
        short handle_size, lhs_sym_num;
  
        /* set up direct reference to tables to drive the parser */
  
        production_tab = production_table();
        action_tab     = action_table();
        reduce_tab     = reduce_table();
  
        /* initialize the action encapsulation object */
        init_actions();
  
        /* do user initialization */
        user_init();
  
        /* get the first token */
        cur_token = scan();
  
        /* push dummy Symbol with start state to get us underway */
        stack.removeAllElements();
        stack.push(new Symbol(0, start_state()));
        tos = 0;
  
        /* continue until we are told to stop */
        for (_done_parsing = false; !_done_parsing; )
          {
            /* Check current token for freshness. */
            if (cur_token.used_by_parser)
              throw new Error("Symbol recycling detected (fix your scanner).");
  
            /* current state is always on the top of the stack */
  
            /* look up action out of the current state with the current input */
            act = get_action(((Symbol)stack.peek()).parse_state, cur_token.sym);
  
            /* decode the action -- > 0 encodes shift */
            if (act > 0)
              {
                /* shift to the encoded state by pushing it on the stack */
                cur_token.parse_state = act-1;
                cur_token.used_by_parser = true;
                stack.push(cur_token);
                tos++;
  
                /* advance to the next Symbol */
                cur_token = scan();
              }
            /* if its less than zero, then it encodes a reduce action */
            else if (act < 0)
              {
                /* perform the action for the reduce */
                lhs_sym = do_action((-act)-1, this, stack, tos);
  
                /* look up information about the production */
                lhs_sym_num = production_tab[(-act)-1][0];
                handle_size = production_tab[(-act)-1][1];
  
                /* pop the handle off the stack */
                for (int i = 0; i < handle_size; i++)
                  {
                    stack.pop();
                    tos--;
                  }
  
                /* look up the state to go to from the one popped back to */
                act = get_reduce(((Symbol)stack.peek()).parse_state, lhs_sym_num);
  
                /* shift to that state */
                lhs_sym.parse_state = act;
                lhs_sym.used_by_parser = true;
                stack.push(lhs_sym);
                tos++;
              }
            /* finally if the entry is zero, we have an error */
            else if (act == 0)
              {
                /* call user syntax error reporting routine */
                syntax_error(cur_token);
  
                /* try to error recover */
                if (!error_recovery(false))
                  {
                    /* if that fails give up with a fatal syntax error */
                    unrecovered_syntax_error(cur_token);
  
                    /* just in case that wasn't fatal enough, end parse */
                    done_parsing();
                  } else {
                    lhs_sym = (Symbol)stack.peek();
                  }
              }
          }
        return lhs_sym;
      }
  
    /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
  
    /** Write a debugging message to System.err for the debugging version
     *  of the parser.
     *
     * @param mess the text of the debugging message.
     */
    public void debug_message(String mess)
      {
        System.err.println(mess);
      }
  
    /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
  
    /** Dump the parse stack for debugging purposes. */
    public void dump_stack()
      {
        if (stack == null)
          {
            debug_message("# Stack dump requested, but stack is null");
            return;
          }
  
        debug_message("============ Parse Stack Dump ============");
  
        /* dump the stack */
        for (int i=0; i<stack.size(); i++)
          {
            debug_message("Symbol: " + ((Symbol)stack.elementAt(i)).sym +
                          " State: " + ((Symbol)stack.elementAt(i)).parse_state);
          }
        debug_message("==========================================");
      }
  
    /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
  
    /** Do debug output for a reduce.
     *
     * @param prod_num  the production we are reducing with.
     * @param nt_num    the index of the LHS non terminal.
     * @param rhs_size  the size of the RHS.
     */
    public void debug_reduce(int prod_num, int nt_num, int rhs_size)
      {
        debug_message("# Reduce with prod #" + prod_num + " [NT=" + nt_num +
                      ", " + "SZ=" + rhs_size + "]");
      }
  
    /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
  
    /** Do debug output for shift.
     *
     * @param shift_tkn the Symbol being shifted onto the stack.
     */
    public void debug_shift(Symbol shift_tkn)
      {
        debug_message("# Shift under term #" + shift_tkn.sym +
                      " to state #" + shift_tkn.parse_state);
      }
  
    /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
  
    /** Do debug output for stack state. [CSA]
     */
    public void debug_stack() {
        StringBuffer sb=new StringBuffer("## STACK:");
        for (int i=0; i<stack.size(); i++) {
            Symbol s = (Symbol) stack.elementAt(i);
            sb.append(" <state "+s.parse_state+", sym "+s.sym+">");
            if ((i%3)==2 || (i==(stack.size()-1))) {
                debug_message(sb.toString());
                sb = new StringBuffer("         ");
            }
        }
    }
  
    /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
  
    /** Perform a parse with debugging output.  This does exactly the
     *  same things as parse(), except that it calls debug_shift() and
     *  debug_reduce() when shift and reduce moves are taken by the parser
     *  and produces various other debugging messages.
     */
    public Symbol debug_parse()
      throws java.lang.Exception
      {
        /* the current action code */
        int act;
  
        /* the Symbol/stack element returned by a reduce */
        Symbol lhs_sym = null;
  
        /* information about production being reduced with */
        short handle_size, lhs_sym_num;
  
        /* set up direct reference to tables to drive the parser */
        production_tab = production_table();
        action_tab     = action_table();
        reduce_tab     = reduce_table();
  
        debug_message("# Initializing parser");
  
        /* initialize the action encapsulation object */
        init_actions();
  
        /* do user initialization */
        user_init();
  
        /* the current Symbol */
        cur_token = scan();
  
        debug_message("# Current Symbol is #" + cur_token.sym);
  
        /* push dummy Symbol with start state to get us underway */
        stack.removeAllElements();
        stack.push(new Symbol(0, start_state()));
        tos = 0;
  
        /* continue until we are told to stop */
        for (_done_parsing = false; !_done_parsing; )
          {
            /* Check current token for freshness. */
            if (cur_token.used_by_parser)
              throw new Error("Symbol recycling detected (fix your scanner).");
  
            /* current state is always on the top of the stack */
            //debug_stack();
  
            /* look up action out of the current state with the current input */
            act = get_action(((Symbol)stack.peek()).parse_state, cur_token.sym);
  
            /* decode the action -- > 0 encodes shift */
            if (act > 0)
              {
                /* shift to the encoded state by pushing it on the stack */
                cur_token.parse_state = act-1;
                cur_token.used_by_parser = true;
                debug_shift(cur_token);
                stack.push(cur_token);
                tos++;
  
                /* advance to the next Symbol */
                cur_token = scan();
                debug_message("# Current token is " + cur_token);
              }
            /* if its less than zero, then it encodes a reduce action */
            else if (act < 0)
              {
                /* perform the action for the reduce */
                lhs_sym = do_action((-act)-1, this, stack, tos);
  
                /* look up information about the production */
                lhs_sym_num = production_tab[(-act)-1][0];
                handle_size = production_tab[(-act)-1][1];
  
                debug_reduce((-act)-1, lhs_sym_num, handle_size);
  
                /* pop the handle off the stack */
                for (int i = 0; i < handle_size; i++)
                  {
                    stack.pop();
                    tos--;
                  }
  
                /* look up the state to go to from the one popped back to */
                act = get_reduce(((Symbol)stack.peek()).parse_state, lhs_sym_num);
                debug_message("# Reduce rule: top state " +
                               ((Symbol)stack.peek()).parse_state +
                               ", lhs sym " + lhs_sym_num + " -> state " + act);
  
                /* shift to that state */
                lhs_sym.parse_state = act;
                lhs_sym.used_by_parser = true;
                stack.push(lhs_sym);
                tos++;
  
                debug_message("# Goto state #" + act);
              }
            /* finally if the entry is zero, we have an error */
            else if (act == 0)
              {
                /* call user syntax error reporting routine */
                syntax_error(cur_token);
  
                /* try to error recover */
                if (!error_recovery(true))
                  {
                    /* if that fails give up with a fatal syntax error */
                    unrecovered_syntax_error(cur_token);
  
                    /* just in case that wasn't fatal enough, end parse */
                    done_parsing();
                  } else {
                    lhs_sym = (Symbol)stack.peek();
                  }
              }
          }
        return lhs_sym;
      }
  
    /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
    /* Error recovery code */
    /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
  
    /** Attempt to recover from a syntax error.  This returns false if recovery
     *  fails, true if it succeeds.  Recovery happens in 4 steps.  First we
     *  pop the parse stack down to a point at which we have a shift out
     *  of the top-most state on the error Symbol.  This represents the
     *  initial error recovery configuration.  If no such configuration is
     *  found, then we fail.  Next a small number of "lookahead" or "parse
     *  ahead" Symbols are read into a buffer.  The size of this buffer is
     *  determined by error_sync_size() and determines how many Symbols beyond
     *  the error must be matched to consider the recovery a success.  Next,
     *  we begin to discard Symbols in attempt to get past the point of error
     *  to a point where we can continue parsing.  After each Symbol, we attempt
     *  to "parse ahead" though the buffered lookahead Symbols.  The "parse ahead"
     *  process simulates that actual parse, but does not modify the real
     *  parser's configuration, nor execute any actions. If we can  parse all
     *  the stored Symbols without error, then the recovery is considered a
     *  success.  Once a successful recovery point is determined, we do an
     *  actual parse over the stored input -- modifying the real parse
     *  configuration and executing all actions.  Finally, we return the the
     *  normal parser to continue with the overall parse.
     *
     * @param debug should we produce debugging messages as we parse.
     */
    protected boolean error_recovery(boolean debug)
      throws java.lang.Exception
      {
        if (debug) debug_message("# Attempting error recovery");
  
        /* first pop the stack back into a state that can shift on error and
           do that shift (if that fails, we fail) */
        if (!find_recovery_config(debug))
          {
            if (debug) debug_message("# Error recovery fails");
            return false;
          }
  
        /* read ahead to create lookahead we can parse multiple times */
        read_lookahead();
  
        /* repeatedly try to parse forward until we make it the required dist */
        for (;;)
          {
            /* try to parse forward, if it makes it, bail out of loop */
            if (debug) debug_message("# Trying to parse ahead");
            if (try_parse_ahead(debug))
              {
                break;
              }
  
            /* if we are now at EOF, we have failed */
            if (lookahead[0].sym == EOF_sym())
              {
                if (debug) debug_message("# Error recovery fails at EOF");
                return false;
              }
  
            /* otherwise, we consume another Symbol and try again */
            if (debug)
            debug_message("# Consuming Symbol #" + cur_err_token().sym);
            restart_lookahead();
          }
  
        /* we have consumed to a point where we can parse forward */
        if (debug) debug_message("# Parse-ahead ok, going back to normal parse");
  
        /* do the real parse (including actions) across the lookahead */
        parse_lookahead(debug);
  
        /* we have success */
        return true;
      }
  
    /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
  
    /** Determine if we can shift under the special error Symbol out of the
     *  state currently on the top of the (real) parse stack.
     */
    protected boolean shift_under_error()
      {
        /* is there a shift under error Symbol */
        return get_action(((Symbol)stack.peek()).parse_state, error_sym()) > 0;
      }
  
    /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
  
    /** Put the (real) parse stack into error recovery configuration by
     *  popping the stack down to a state that can shift on the special
     *  error Symbol, then doing the shift.  If no suitable state exists on
     *  the stack we return false
     *
     * @param debug should we produce debugging messages as we parse.
     */
    protected boolean find_recovery_config(boolean debug)
      {
        Symbol error_token;
        int act;
  
        if (debug) debug_message("# Finding recovery state on stack");
  
        /* Remember the right-position of the top symbol on the stack */
        int right_pos = ((Symbol)stack.peek()).right;
        int left_pos  = ((Symbol)stack.peek()).left;
  
        /* pop down until we can shift under error Symbol */
        while (!shift_under_error())
          {
            /* pop the stack */
            if (debug)
              debug_message("# Pop stack by one, state was # " +
                            ((Symbol)stack.peek()).parse_state);
            left_pos = ((Symbol)stack.pop()).left;
            tos--;
  
            /* if we have hit bottom, we fail */
            if (stack.empty())
              {
                if (debug) debug_message("# No recovery state found on stack");
                return false;
              }
          }
  
        /* state on top of the stack can shift under error, find the shift */
        act = get_action(((Symbol)stack.peek()).parse_state, error_sym());
        if (debug)
          {
            debug_message("# Recover state found (#" +
                          ((Symbol)stack.peek()).parse_state + ")");
            debug_message("# Shifting on error to state #" + (act-1));
          }
  
        /* build and shift a special error Symbol */
        error_token = new Symbol(error_sym(), left_pos, right_pos);
        error_token.parse_state = act-1;
        error_token.used_by_parser = true;
        stack.push(error_token);
        tos++;
  
        return true;
      }
  
    /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
  
    /** Lookahead Symbols used for attempting error recovery "parse aheads". */
    protected Symbol lookahead[];
  
    /** Position in lookahead input buffer used for "parse ahead". */
    protected int lookahead_pos;
  
    /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
  
    /** Read from input to establish our buffer of "parse ahead" lookahead
     *  Symbols.
     */
    protected void read_lookahead() throws java.lang.Exception
      {
        /* create the lookahead array */
        lookahead = new Symbol[error_sync_size()];
  
        /* fill in the array */
        for (int i = 0; i < error_sync_size(); i++)
          {
            lookahead[i] = cur_token;
            cur_token = scan();
          }
  
        /* start at the beginning */
        lookahead_pos = 0;
      }
  
    /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
  
    /** Return the current lookahead in our error "parse ahead" buffer. */
    protected Symbol cur_err_token() { return lookahead[lookahead_pos]; }
  
    /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
  
    /** Advance to next "parse ahead" input Symbol. Return true if we have
     *  input to advance to, false otherwise.
     */
    protected boolean advance_lookahead()
      {
        /* advance the input location */
        lookahead_pos++;
  
        /* return true if we didn't go off the end */
        return lookahead_pos < error_sync_size();
      }
  
    /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
  
    /** Reset the parse ahead input to one Symbol past where we started error
     *  recovery (this consumes one new Symbol from the real input).
     */
    protected void restart_lookahead() throws java.lang.Exception
      {
        /* move all the existing input over */
        for (int i = 1; i < error_sync_size(); i++)
          lookahead[i-1] = lookahead[i];
  
        /* read a new Symbol into the last spot */
        cur_token = scan();
        lookahead[error_sync_size()-1] = cur_token;
  
        /* reset our internal position marker */
        lookahead_pos = 0;
      }
  
    /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
  
    /** Do a simulated parse forward (a "parse ahead") from the current
     *  stack configuration using stored lookahead input and a virtual parse
     *  stack.  Return true if we make it all the way through the stored
     *  lookahead input without error. This basically simulates the action of
     *  parse() using only our saved "parse ahead" input, and not executing any
     *  actions.
     *
     * @param debug should we produce debugging messages as we parse.
     */
    protected boolean try_parse_ahead(boolean debug)
      throws java.lang.Exception
      {
        int act;
        short lhs, rhs_size;
  
        /* create a virtual stack from the real parse stack */
        virtual_parse_stack vstack = new virtual_parse_stack(stack);
  
        /* parse until we fail or get past the lookahead input */
        for (;;)
          {
            /* look up the action from the current state (on top of stack) */
            act = get_action(vstack.top(), cur_err_token().sym);
  
            /* if its an error, we fail */
            if (act == 0) return false;
  
            /* > 0 encodes a shift */
            if (act > 0)
              {
                /* push the new state on the stack */
                vstack.push(act-1);
  
                if (debug) debug_message("# Parse-ahead shifts Symbol #" +
                         cur_err_token().sym + " into state #" + (act-1));
  
                /* advance simulated input, if we run off the end, we are done */
                if (!advance_lookahead()) return true;
              }
            /* < 0 encodes a reduce */
            else
              {
                /* if this is a reduce with the start production we are done */
                if ((-act)-1 == start_production())
                  {
                    if (debug) debug_message("# Parse-ahead accepts");
                    return true;
                  }
  
                /* get the lhs Symbol and the rhs size */
                lhs = production_tab[(-act)-1][0];
                rhs_size = production_tab[(-act)-1][1];
  
                /* pop handle off the stack */
                for (int i = 0; i < rhs_size; i++)
                  vstack.pop();
  
                if (debug)
                  debug_message("# Parse-ahead reduces: handle size = " +
                    rhs_size + " lhs = #" + lhs + " from state #" + vstack.top());
  
                /* look up goto and push it onto the stack */
                vstack.push(get_reduce(vstack.top(), lhs));
                if (debug)
                  debug_message("# Goto state #" + vstack.top());
              }
          }
      }
  
    /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
  
    /** Parse forward using stored lookahead Symbols.  In this case we have
     *  already verified that parsing will make it through the stored lookahead
     *  Symbols and we are now getting back to the point at which we can hand
     *  control back to the normal parser.  Consequently, this version of the
     *  parser performs all actions and modifies the real parse configuration.
     *  This returns once we have consumed all the stored input or we accept.
     *
     * @param debug should we produce debugging messages as we parse.
     */
    protected void parse_lookahead(boolean debug)
      throws java.lang.Exception
      {
        /* the current action code */
        int act;
  
        /* the Symbol/stack element returned by a reduce */
        Symbol lhs_sym = null;
  
        /* information about production being reduced with */
        short handle_size, lhs_sym_num;
  
        /* restart the saved input at the beginning */
        lookahead_pos = 0;
  
        if (debug)
          {
            debug_message("# Reparsing saved input with actions");
            debug_message("# Current Symbol is #" + cur_err_token().sym);
            debug_message("# Current state is #" +
                          ((Symbol)stack.peek()).parse_state);
          }
  
        /* continue until we accept or have read all lookahead input */
        while(!_done_parsing)
          {
            /* current state is always on the top of the stack */
  
            /* look up action out of the current state with the current input */
            act =
              get_action(((Symbol)stack.peek()).parse_state, cur_err_token().sym);
  
            /* decode the action -- > 0 encodes shift */
            if (act > 0)
              {
                /* shift to the encoded state by pushing it on the stack */
                cur_err_token().parse_state = act-1;
                cur_err_token().used_by_parser = true;
                if (debug) debug_shift(cur_err_token());
                stack.push(cur_err_token());
                tos++;
  
                /* advance to the next Symbol, if there is none, we are done */
                if (!advance_lookahead())
                  {
                    if (debug) debug_message("# Completed reparse");
  
                    /* scan next Symbol so we can continue parse */
                    // BUGFIX by Chris Harris <ckharris@ucsd.edu>:
                    //   correct a one-off error by commenting out
                    //   this next line.
                    /*cur_token = scan();*/
  
                    /* go back to normal parser */
                    return;
                  }
  
                if (debug)
                  debug_message("# Current Symbol is #" + cur_err_token().sym);
              }
            /* if its less than zero, then it encodes a reduce action */
            else if (act < 0)
              {
                /* perform the action for the reduce */
                lhs_sym = do_action((-act)-1, this, stack, tos);
  
                /* look up information about the production */
                lhs_sym_num = production_tab[(-act)-1][0];
                handle_size = production_tab[(-act)-1][1];
  
                if (debug) debug_reduce((-act)-1, lhs_sym_num, handle_size);
  
                /* pop the handle off the stack */
                for (int i = 0; i < handle_size; i++)
                  {
                    stack.pop();
                    tos--;
                  }
  
                /* look up the state to go to from the one popped back to */
                act = get_reduce(((Symbol)stack.peek()).parse_state, lhs_sym_num);
  
                /* shift to that state */
                lhs_sym.parse_state = act;
                lhs_sym.used_by_parser = true;
                stack.push(lhs_sym);
                tos++;
  
                if (debug) debug_message("# Goto state #" + act);
  
              }
            /* finally if the entry is zero, we have an error
               (shouldn't happen here, but...)*/
            else if (act == 0)
              {
                report_fatal_error("Syntax error", lhs_sym);
                return;
              }
          }
  
  
      }
  
    /*-----------------------------------------------------------*/
  
    /** Utility function: unpacks parse tables from strings */
    protected static short[][] unpackFromStrings(String[] sa)
      {
        // Concatanate initialization strings.
        StringBuffer sb = new StringBuffer(sa[0]);
        for (int i=1; i<sa.length; i++)
          sb.append(sa[i]);
        int n=0; // location in initialization string
        int size1 = (((int)sb.charAt(n))<<16) | ((int)sb.charAt(n+1)); n+=2;
        short[][] result = new short[size1][];
        for (int i=0; i<size1; i++) {
          int size2 = (((int)sb.charAt(n))<<16) | ((int)sb.charAt(n+1)); n+=2;
          result[i] = new short[size2];
          for (int j=0; j<size2; j++)
            result[i][j] = (short) (sb.charAt(n++)-2);
        }
        return result;
      }
  }
  