symbol


1   package java_cup;
2   
3   /** This abstract class serves as the base class for grammar symbols (i.e.,
4    * both terminals and non-terminals).  Each symbol has a name string, and
5    * a string giving the type of object that the symbol will be represented by
6    * on the runtime parse stack.  In addition, each symbol maintains a use count
7    * in order to detect symbols that are declared but never used, and an index
8    * number that indicates where it appears in parse tables (index numbers are
9    * unique within terminals or non terminals, but not across both).
10   *
11   * @see     java_cup.terminal
12   * @see     java_cup.non_terminal
13   * @version last updated: 7/3/96
14   * @author  Frank Flannery
15   */
16  public abstract class symbol {
17     /*-----------------------------------------------------------*/
18     /*--- Constructor(s) ----------------------------------------*/
19     /*-----------------------------------------------------------*/
20  
21     /** Full constructor.
22      * @param nm the name of the symbol.
23      * @param tp a string with the type name.
24      */
25     public symbol(String   nm, String   tp)
26       {
27         /* sanity check */
28         if (nm == null) nm = "";
29  
30         /* apply default if no type given */
31         if (tp == null) tp = "Object";
32  
33         _name = nm;
34         _stack_type = tp;
35       }
36  
37    /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
38  
39     /** Constructor with default type. 
40      * @param nm the name of the symbol.
41      */
42     public symbol(String   nm)
43       {
44         this(nm, null);
45       }
46  
47     /*-----------------------------------------------------------*/
48     /*--- (Access to) Instance Variables ------------------------*/
49     /*-----------------------------------------------------------*/
50  
51     /** String for the human readable name of the symbol. */
52     protected String   _name; 
53   
54     /** String for the human readable name of the symbol. */
55     public String   name() {return _name;}
56  
57    /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
58  
59     /** String for the type of object used for the symbol on the parse stack. */
60     protected String   _stack_type;
61  
62     /** String for the type of object used for the symbol on the parse stack. */
63     public String   stack_type() {return _stack_type;}
64  
65    /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
66  
67     /** Count of how many times the symbol appears in productions. */
68     protected int _use_count = 0;
69  
70     /** Count of how many times the symbol appears in productions. */
71     public int use_count() {return _use_count;}
72  
73     /** Increment the use count. */ 
74     public void note_use() {_use_count++;}
75   
76    /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
77   
78    /** Index of this symbol (terminal or non terminal) in the parse tables.
79     *  Note: indexes are unique among terminals and unique among non terminals,
80     *  however, a terminal may have the same index as a non-terminal, etc. 
81     */
82     protected int _index;
83   
84    /** Index of this symbol (terminal or non terminal) in the parse tables.
85     *  Note: indexes are unique among terminals and unique among non terminals,
86     *  however, a terminal may have the same index as a non-terminal, etc. 
87     */
88     public int index() {return _index;}
89  
90    /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
91  
92    /** Indicate if this is a non-terminal.  Here in the base class we
93     *  don't know, so this is abstract.  
94     */
95    public abstract boolean is_non_term();
96  
97    /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
98  
99    /** Convert to a string. */
100   public String   toString()
101     {
102       return name();
103     }
104 
105   /*-----------------------------------------------------------*/
106 
107 }
108
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