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      1 package java_cup;
      2 
      3 /** This class represents a transition in an LALR viable prefix recognition
      4  *  machine.  Transitions can be under terminals for non-terminals.  They are
      5  *  internally linked together into singly linked lists containing all the
      6  *  transitions out of a single state via the _next field.
      7  *
      8  * @see     java_cup.lalr_state
      9  * @version last updated: 11/25/95
     10  * @author  Scott Hudson
     11  *
     12  */
     13 public class lalr_transition {
     14 
     15   /*-----------------------------------------------------------*/
     16   /*--- Constructor(s) ----------------------------------------*/
     17   /*-----------------------------------------------------------*/
     18 
     19   /** Full constructor.
     20    * @param on_sym  symbol we are transitioning on.
     21    * @param to_st   state we transition to.
     22    * @param nxt     next transition in linked list.
     23    */
     24   public lalr_transition(symbol on_sym, lalr_state to_st, lalr_transition nxt)
     25     throws internal_error
     26     {
     27       /* sanity checks */
     28       if (on_sym == null)
     29     throw new internal_error("Attempt to create transition on null symbol");
     30       if (to_st == null)
     31     throw new internal_error("Attempt to create transition to null state");
     32 
     33       /* initialize */
     34       _on_symbol = on_sym;
     35       _to_state  = to_st;
     36       _next      = nxt;
     37     }
     38 
     39   /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
     40 
     41   /** Constructor with null next.
     42    * @param on_sym  symbol we are transitioning on.
     43    * @param to_st   state we transition to.
     44    */
     45   public lalr_transition(symbol on_sym, lalr_state to_st) throws internal_error
     46     {
     47       this(on_sym, to_st, null);
     48     }
     49 
     50   /*-----------------------------------------------------------*/
     51   /*--- (Access to) Instance Variables ------------------------*/
     52   /*-----------------------------------------------------------*/
     53 
     54   /** The symbol we make the transition on. */
     55   protected symbol _on_symbol;
     56 
     57   /** The symbol we make the transition on. */
     58   public symbol on_symbol() {return _on_symbol;}
     59 
     60   /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
     61 
     62   /** The state we transition to. */
     63   protected lalr_state _to_state;
     64 
     65   /** The state we transition to. */
     66   public lalr_state to_state() {return _to_state;}
     67 
     68   /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
     69 
     70   /** Next transition in linked list of transitions out of a state */
     71   protected lalr_transition _next;
     72 
     73   /** Next transition in linked list of transitions out of a state */
     74   public lalr_transition next() {return _next;}
     75 
     76   /*-----------------------------------------------------------*/
     77   /*--- General Methods ---------------------------------------*/
     78   /*-----------------------------------------------------------*/
     79 
     80   /** Convert to a string. */
     81   public String toString()
     82     {
     83       String result;
     84 
     85       result = "transition on " + on_symbol().name() + " to state [";
     86       result += _to_state.index();
     87       result += "]";
     88 
     89       return result;
     90     }
     91 
     92   /*-----------------------------------------------------------*/
     93 };
     94