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production.java

package java_cup;

import java.util.Hashtable;
import java.util.Enumeration;

/** This class represents a production in the grammar.  It contains
 *  a LHS non terminal, and an array of RHS symbols.  As various 
 *  transformations are done on the RHS of the production, it may shrink.
 *  As a result a separate length is always maintained to indicate how much
 *  of the RHS array is still valid.<p>
 * 
 *  I addition to construction and manipulation operations, productions provide
 *  methods for factoring out actions (see  remove_embedded_actions()), for
 *  computing the nullability of the production (i.e., can it derive the empty
 *  string, see check_nullable()), and operations for computing its first
 *  set (i.e., the set of terminals that could appear at the beginning of some
 *  string derived from the production, see check_first_set()).
 * 
 * @see     java_cup.production_part
 * @see     java_cup.symbol_part
 * @see     java_cup.action_part
 * @version last updated: 7/3/96
 * @author  Frank Flannery
 */

00027 public class production {

  /*-----------------------------------------------------------*/
  /*--- Constructor(s) ----------------------------------------*/
  /*-----------------------------------------------------------*/

  /** Full constructor.  This constructor accepts a LHS non terminal,
   *  an array of RHS parts (including terminals, non terminals, and 
   *  actions), and a string for a final reduce action.   It does several
   *  manipulations in the process of  creating a production object.
   *  After some validity checking it translates labels that appear in
   *  actions into code for accessing objects on the runtime parse stack.
   *  It them merges adjacent actions if they appear and moves any trailing
   *  action into the final reduce actions string.  Next it removes any
   *  embedded actions by factoring them out with new action productions.  
   *  Finally it assigns a unique index to the production.<p>
   *
   *  Factoring out of actions is accomplished by creating new "hidden"
   *  non terminals.  For example if the production was originally: <pre>
   *    A ::= B {action} C D
   *  </pre>
   *  then it is factored into two productions:<pre>
   *    A ::= B X C D
   *    X ::= {action}
   *  </pre> 
   *  (where X is a unique new non terminal).  This has the effect of placing
   *  all actions at the end where they can be handled as part of a reduce by
   *  the parser.
   */
00056   public production(
    non_terminal    lhs_sym, 
    production_part rhs_parts[], 
    int             rhs_l,
    String          action_str)
    throws internal_error
    {
      int         i;
      action_part tail_action;
      String declare_str;
      int rightlen = rhs_l;

      /* remember the length */
      if (rhs_l >= 0)
      _rhs_length = rhs_l;
      else if (rhs_parts != null)
      _rhs_length = rhs_parts.length;
      else
      _rhs_length = 0;
      
      /* make sure we have a valid left-hand-side */
      if (lhs_sym == null) 
      throw new internal_error(
        "Attempt to construct a production with a null LHS");

      /* I'm not translating labels anymore, I'm adding code to declare
       labels as valid variables.  This way, the users code string is
       untouched 
       6/96 frankf */

      /* check if the last part of the right hand side is an action.  If
         it is, it won't be on the stack, so we don't want to count it 
       in the rightlen.  Then when we search down the stack for a
         Symbol, we don't try to search past action */

      if (rhs_l > 0) {
      if (rhs_parts[rhs_l - 1].is_action()) {
        rightlen = rhs_l - 1;
      } else {
        rightlen = rhs_l;
      }
      }

      /* get the generated declaration code for the necessary labels. */
      declare_str = declare_labels(
                rhs_parts, rightlen, action_str);

      if (action_str == null) 
      action_str = declare_str;
      else 
      action_str = declare_str + action_str;            

      /* count use of lhs */
      lhs_sym.note_use();

      /* create the part for left-hand-side */
      _lhs = new symbol_part(lhs_sym);

      /* merge adjacent actions (if any) */
      _rhs_length = merge_adjacent_actions(rhs_parts, _rhs_length);

      /* strip off any trailing action */
      tail_action = strip_trailing_action(rhs_parts, _rhs_length);
      if (tail_action != null) _rhs_length--;

      /* Why does this run through the right hand side happen
       over and over?  here a quick combination of two 
       prior runs plus one I wanted of my own
       frankf 6/25/96 */
      /* allocate and copy over the right-hand-side */
      /* count use of each rhs symbol */
      _rhs = new production_part[_rhs_length];
      for (i=0; i<_rhs_length; i++) {
      _rhs[i] = rhs_parts[i];
      if (!_rhs[i].is_action()) {
        ((symbol_part)_rhs[i]).the_symbol().note_use();
        if (((symbol_part)_rhs[i]).the_symbol() instanceof terminal) {
          _rhs_prec = 
            ((terminal)((symbol_part)_rhs[i]).the_symbol()).precedence_num();
          _rhs_assoc = 
            ((terminal)((symbol_part)_rhs[i]).the_symbol()).precedence_side();
        }
      }
      }

      /*now action string is really declaration string, so put it in front!
      6/14/96 frankf */
      if (action_str == null) action_str = "";
      if (tail_action != null && tail_action.code_string() != null)
      action_str = action_str + "\t\t" +  tail_action.code_string();

      /* stash the action */
      _action = new action_part(action_str);

      /* rewrite production to remove any embedded actions */
      remove_embedded_actions();

      /* assign an index */
      _index = next_index++;

      /* put us in the global collection of productions */
      _all.put(new Integer(_index),this);

      /* put us in the production list of the lhs non terminal */
      lhs_sym.add_production(this);
    }

  /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/

  /** Constructor with no action string. */
00166   public production(
    non_terminal    lhs_sym, 
    production_part rhs_parts[], 
    int             rhs_l)
    throws internal_error
    {
      this(lhs_sym,rhs_parts,rhs_l,null);
    }
 
  /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/

  /* Constructor with precedence and associativity of production
     contextually define */
  public production(
    non_terminal    lhs_sym, 
    production_part rhs_parts[], 
    int             rhs_l,
    String          action_str,
    int               prec_num,
    int             prec_side)
    throws internal_error
    {
      this(lhs_sym,rhs_parts,rhs_l,action_str);
      
      /* set the precedence */
      set_precedence_num(prec_num);
      set_precedence_side(prec_side);
    }

  /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/ 
     
  /* Constructor w/ no action string and contextual precedence
     defined */
  public production(
    non_terminal    lhs_sym, 
    production_part rhs_parts[], 
    int             rhs_l,
    int             prec_num,
    int             prec_side)
    throws internal_error
    {
      this(lhs_sym,rhs_parts,rhs_l,null);
      /* set the precedence */
      set_precedence_num(prec_num);
      set_precedence_side(prec_side);
    }

  /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/

  /*-----------------------------------------------------------*/
  /*--- (Access to) Static (Class) Variables ------------------*/
  /*-----------------------------------------------------------*/
 
    
  /** Table of all productions.  Elements are stored using their index as 
   *  the key.
   */
00223   protected static Hashtable _all = new Hashtable();
 
  /** Access to all productions. */
00226   public static Enumeration all() {return _all.elements();}

    /** Lookup a production by index. */
00229   public static production find(int indx) {
    return (production) _all.get(new Integer(indx));
  }

  /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
 
  /** Total number of productions. */
00236   public static int number() {return _all.size();}

  /** Static counter for assigning unique index numbers. */
00239   protected static int next_index;

  /*-----------------------------------------------------------*/
  /*--- (Access to) Instance Variables ------------------------*/
  /*-----------------------------------------------------------*/

  /** The left hand side non-terminal. */
00246   protected symbol_part _lhs;

  /** The left hand side non-terminal. */
00249   public symbol_part lhs() {return _lhs;}


  /** The precedence of the rule */
00253   protected int _rhs_prec = -1;
  protected int _rhs_assoc = -1;

  /** Access to the precedence of the rule */
00257   public int precedence_num() { return _rhs_prec; }
  public int precedence_side() { return _rhs_assoc; }

  /** Setting the precedence of a rule */
00261   public void set_precedence_num(int prec_num) {  
    _rhs_prec = prec_num;
  }
  public void set_precedence_side(int prec_side) { 
    _rhs_assoc = prec_side;
  }

  /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/

  /** A collection of parts for the right hand side. */
00271   protected production_part _rhs[];

  /** Access to the collection of parts for the right hand side. */
00274   public production_part rhs(int indx) throws internal_error
    {
      if (indx >= 0 && indx < _rhs_length)
      return _rhs[indx];
      else
      throw new internal_error(
        "Index out of range for right hand side of production");
    }

  /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/

  /** How much of the right hand side array we are presently using. */
00286   protected int _rhs_length;

  /** How much of the right hand side array we are presently using. */
00289   public int rhs_length() {return _rhs_length;}

  /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/

  /** An action_part containing code for the action to be performed when we 
   *  reduce with this production. 
   */
00296   protected action_part _action;

  /** An action_part containing code for the action to be performed when we 
   *  reduce with this production. 
   */
00301   public action_part action() {return _action;}

  /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/

  /** Index number of the production. */
00306   protected int _index;

  /** Index number of the production. */
00309   public int index() {return _index;}

  /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/

  /** Count of number of reductions using this production. */
00314   protected int _num_reductions = 0;

  /** Count of number of reductions using this production. */
00317   public int num_reductions() {return _num_reductions;}

  /** Increment the count of reductions with this non-terminal */
00320   public void note_reduction_use() {_num_reductions++;}

  /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/

  /** Is the nullability of the production known or unknown? */
00325   protected boolean _nullable_known = false;

  /** Is the nullability of the production known or unknown? */
00328   public boolean nullable_known() {return _nullable_known;}

  /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/

  /** Nullability of the production (can it derive the empty string). */
00333   protected boolean _nullable = false;

  /** Nullability of the production (can it derive the empty string). */
00336   public boolean nullable() {return _nullable;}

  /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/

  /** First set of the production.  This is the set of terminals that 
   *  could appear at the front of some string derived from this production.
   */
00343   protected terminal_set _first_set = new terminal_set();

  /** First set of the production.  This is the set of terminals that 
   *  could appear at the front of some string derived from this production.
   */
00348   public terminal_set first_set() {return _first_set;}

  /*-----------------------------------------------------------*/
  /*--- Static Methods ----------------------------------------*/
  /*-----------------------------------------------------------*/

  /** Determine if a given character can be a label id starter. 
   * @param c the character in question. 
   */
00357   protected static boolean is_id_start(char c)
    {
      return (c >= 'a' && c <= 'z') || (c >= 'A' && c <= 'Z') || (c == '_');

      //later need to handle non-8-bit chars here
    }

  /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/

  /** Determine if a character can be in a label id. 
   * @param c the character in question.
   */
00369   protected static boolean is_id_char(char c)
    {
      return is_id_start(c) || (c >= '0' && c <= '9');
    }

  /*-----------------------------------------------------------*/
  /*--- General Methods ---------------------------------------*/
  /*-----------------------------------------------------------*/
  

  /** Return label declaration code
   * @param labelname    the label name
   * @param stack_type   the stack type of label?
   * @author frankf
   */ 
00384   protected String make_declaration(
                            String  labelname,
                            String  stack_type,
                            int     offset)
    {
      String ret;

      /* Put in the left/right value labels */
      if (emit.lr_values())
        ret = "\t\tint " + labelname + "left = ((java_cup.runtime.Symbol)" + 
        emit.pre("stack") + ".elementAt(" + emit.pre("top") + 
        "-" + offset + ")).left;\n" +
        "\t\tint " + labelname + "right = ((java_cup.runtime.Symbol)" + 
        emit.pre("stack") + ".elementAt(" + emit.pre("top") +
        "-" + offset + ")).right;\n";
      else ret = "";

      /* otherwise, just declare label. */
      return ret + "\t\t" + stack_type + " " + labelname + " = (" + stack_type + 
        ")((" + "java_cup.runtime.Symbol) " + emit.pre("stack") + ".elementAt(" + emit.pre("top") 
        + "-" + offset + ")).value;\n";

    }
  /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/

  /** Declare label names as valid variables within the action string
   * @param rhs          array of RHS parts.
   * @param rhs_len      how much of rhs to consider valid.
   * @param final_action the final action string of the production. 
   * @param lhs_type     the object type associated with the LHS symbol.
   */ 
00415   protected String declare_labels(
    production_part  rhs[], 
    int              rhs_len, 
    String           final_action)
    {
      String declaration = "";

      symbol_part part;
      action_part act_part;
      int         pos;

      /* walk down the parts and extract the labels */
      for (pos = 0; pos < rhs_len; pos++)
      {
        if (!rhs[pos].is_action())
          {
            part = (symbol_part)rhs[pos];

            /* if it has a label, make declaration! */
            if (part.label() != null)
            {
              declaration = declaration + 
                make_declaration(part.label(), part.the_symbol().stack_type(), 
                             rhs_len-pos-1);
            }
          }
      }
      return declaration;
    }



  /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/

  /** Helper routine to merge adjacent actions in a set of RHS parts 
   * @param rhs_parts array of RHS parts.
   * @param len       amount of that array that is valid.
   * @return          remaining valid length.
   */
00454   protected int merge_adjacent_actions(production_part rhs_parts[], int len)
    {
      int from_loc, to_loc, merge_cnt;

      /* bail out early if we have no work to do */
      if (rhs_parts == null || len == 0) return 0;

      merge_cnt = 0;
      to_loc = -1;
      for (from_loc=0; from_loc<len; from_loc++)
      {
        /* do we go in the current position or one further */
        if (to_loc < 0 || !rhs_parts[to_loc].is_action() 
                   || !rhs_parts[from_loc].is_action())
          {
            /* next one */
            to_loc++;

            /* clear the way for it */
            if (to_loc != from_loc) rhs_parts[to_loc] = null;
          }

        /* if this is not trivial? */
        if (to_loc != from_loc)
          {
            /* do we merge or copy? */
            if (rhs_parts[to_loc] != null && rhs_parts[to_loc].is_action() && 
              rhs_parts[from_loc].is_action())
            {
              /* merge */
              rhs_parts[to_loc] = new action_part(
              ((action_part)rhs_parts[to_loc]).code_string() +
              ((action_part)rhs_parts[from_loc]).code_string());
              merge_cnt++;
            }
          else
            {
              /* copy */
              rhs_parts[to_loc] = rhs_parts[from_loc];
            }
          }
      }

      /* return the used length */
      return len - merge_cnt;
    }

  /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/

  /** Helper routine to strip a trailing action off rhs and return it
   * @param rhs_parts array of RHS parts.
   * @param len       how many of those are valid.
   * @return          the removed action part.
   */
00508   protected action_part strip_trailing_action(
    production_part rhs_parts[],
    int             len)
    {
      action_part result;

      /* bail out early if we have nothing to do */
      if (rhs_parts == null || len == 0) return null;

      /* see if we have a trailing action */
      if (rhs_parts[len-1].is_action())
      {
        /* snip it out and return it */
        result = (action_part)rhs_parts[len-1];
        rhs_parts[len-1] = null;
        return result;
      }
      else
      return null;
    }

  /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/

  /** Remove all embedded actions from a production by factoring them 
   *  out into individual action production using new non terminals.
   *  if the original production was:  <pre>
   *    A ::= B {action1} C {action2} D 
   *  </pre>
   *  then it will be factored into: <pre>
   *    A ::= B NT$1 C NT$2 D
   *    NT$1 ::= {action1}
   *    NT$2 ::= {action2}
   *  </pre>
   *  where NT$1 and NT$2 are new system created non terminals.
   */

  /* the declarations added to the parent production are also passed along,
     as they should be perfectly valid in this code string, since it
     was originally a code string in the parent, not on its own.
     frank 6/20/96 */
00548   protected void remove_embedded_actions(
         
            ) throws internal_error
    {
      non_terminal new_nt;
      production   new_prod;
      String declare_str;
      
      /* walk over the production and process each action */
      for (int act_loc = 0; act_loc < rhs_length(); act_loc++)
      if (rhs(act_loc).is_action())
        {
          
          
          declare_str = declare_labels(
                  _rhs, act_loc, "");
          /* create a new non terminal for the action production */
          new_nt = non_terminal.create_new();
          new_nt.is_embedded_action = true; /* 24-Mar-1998, CSA */

          /* create a new production with just the action */
          new_prod = new action_production(this, new_nt, null, 0, 
            declare_str + ((action_part)rhs(act_loc)).code_string());

          /* replace the action with the generated non terminal */
          _rhs[act_loc] = new symbol_part(new_nt);
        }
    }

  /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/

  /** Check to see if the production (now) appears to be nullable.
   *  A production is nullable if its RHS could derive the empty string.
   *  This results when the RHS is empty or contains only non terminals
   *  which themselves are nullable.
   */
00584   public boolean check_nullable() throws internal_error
    {
      production_part part;
      symbol          sym;
      int             pos;

      /* if we already know bail out early */
      if (nullable_known()) return nullable();

      /* if we have a zero size RHS we are directly nullable */
      if (rhs_length() == 0)
      {
        /* stash and return the result */
        return set_nullable(true);
      }

      /* otherwise we need to test all of our parts */
      for (pos=0; pos<rhs_length(); pos++)
      {
        part = rhs(pos);

        /* only look at non-actions */
        if (!part.is_action())
          {
            sym = ((symbol_part)part).the_symbol();

            /* if its a terminal we are definitely not nullable */
            if (!sym.is_non_term()) 
            return set_nullable(false);
            /* its a non-term, is it marked nullable */
            else if (!((non_terminal)sym).nullable())
            /* this one not (yet) nullable, so we aren't */
              return false;
          }
      }

      /* if we make it here all parts are nullable */
      return set_nullable(true);
    }

  /** set (and return) nullability */
00625   boolean set_nullable(boolean v)
    {
      _nullable_known = true;
      _nullable = v;
      return v;
    }

  /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/

  /** Update (and return) the first set based on current NT firsts. 
   *  This assumes that nullability has already been computed for all non 
   *  terminals and productions. 
   */
00638   public terminal_set check_first_set() throws internal_error
    {
      int    part;
      symbol sym;

      /* walk down the right hand side till we get past all nullables */
      for (part=0; part<rhs_length(); part++)
      {
        /* only look at non-actions */
        if (!rhs(part).is_action())
          {
            sym = ((symbol_part)rhs(part)).the_symbol();

            /* is it a non-terminal?*/
            if (sym.is_non_term())
            {
              /* add in current firsts from that NT */
              _first_set.add(((non_terminal)sym).first_set());

              /* if its not nullable, we are done */
              if (!((non_terminal)sym).nullable())
                break;
            }
            else
            {
                /* its a terminal -- add that to the set */
              _first_set.add((terminal)sym);

              /* we are done */
              break;
            }
          }
      }

      /* return our updated first set */
      return first_set();
    }

  /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/

  /** Equality comparison. */
00679   public boolean equals(production other)
    {
      if (other == null) return false;
      return other._index == _index;
    }

  /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/

  /** Generic equality comparison. */
00688   public boolean equals(Object other)
    {
      if (!(other instanceof production))
      return false;
      else
      return equals((production)other);
    }

  /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/

  /** Produce a hash code. */
00699   public int hashCode()
    {
      /* just use a simple function of the index */
      return _index*13;
    }

  /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/

  /** Convert to a string. */
00708   public String toString() 
    {
      String result;
      
      /* catch any internal errors */
      try {
        result = "production [" + index() + "]: "; 
        result += ((lhs() != null) ? lhs().toString() : "$$NULL-LHS$$");
        result += " :: = ";
        for (int i = 0; i<rhs_length(); i++)
        result += rhs(i) + " ";
        result += ";";
        if (action()  != null && action().code_string() != null) 
        result += " {" + action().code_string() + "}";

        if (nullable_known())
        if (nullable())
          result += "[NULLABLE]";
        else
          result += "[NOT NULLABLE]";
      } catch (internal_error e) {
      /* crash on internal error since we can't throw it from here (because
         superclass does not throw anything. */
      e.crash();
      result = null;
      }

      return result;
    }

  /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/

  /** Convert to a simpler string. */
00741   public String to_simple_string() throws internal_error
    {
      String result;

      result = ((lhs() != null) ? lhs().the_symbol().name() : "NULL_LHS");
      result += " ::= ";
      for (int i = 0; i < rhs_length(); i++)
      if (!rhs(i).is_action())
        result += ((symbol_part)rhs(i)).the_symbol().name() + " ";

      return result;
    }

  /*-----------------------------------------------------------*/

}

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