+++ /dev/null
-package java_cup;
-
-import java.util.Hashtable;
-import java.util.Enumeration;
-
-/** This class represents a non-terminal symbol in the grammar. Each
- * non terminal has a textual name, an index, and a string which indicates
- * the type of object it will be implemented with at runtime (i.e. the class
- * of object that will be pushed on the parse stack to represent it).
- *
- * @version last updated: 11/25/95
- * @author Scott Hudson
- */
-
-public class non_terminal extends symbol {
-
- /*-----------------------------------------------------------*/
- /*--- Constructor(s) ----------------------------------------*/
- /*-----------------------------------------------------------*/
-
- /** Full constructor.
- * @param nm the name of the non terminal.
- * @param tp the type string for the non terminal.
- */
- public non_terminal(String nm, String tp)
- {
- /* super class does most of the work */
- super(nm, tp);
-
- /* add to set of all non terminals and check for duplicates */
- Object conflict = _all.put(nm,this);
- if (conflict != null)
- // can't throw an exception here because these are used in static
- // initializers, so we crash instead
- // was:
- // throw new internal_error("Duplicate non-terminal ("+nm+") created");
- (new internal_error("Duplicate non-terminal ("+nm+") created")).crash();
-
- /* assign a unique index */
- _index = next_index++;
-
- /* add to by_index set */
- _all_by_index.put(new Integer(_index), this);
- }
-
- /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
-
- /** Constructor with default type.
- * @param nm the name of the non terminal.
- */
- public non_terminal(String nm)
- {
- this(nm, null);
- }
-
- /*-----------------------------------------------------------*/
- /*--- (Access to) Static (Class) Variables ------------------*/
- /*-----------------------------------------------------------*/
-
- /** Table of all non-terminals -- elements are stored using name strings
- * as the key
- */
- protected static Hashtable _all = new Hashtable();
-
- /** Access to all non-terminals. */
- public static Enumeration all() {return _all.elements();}
-
- /** lookup a non terminal by name string */
- public static non_terminal find(String with_name)
- {
- if (with_name == null)
- return null;
- else
- return (non_terminal)_all.get(with_name);
- }
-
- /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
-
- /** Table of all non terminals indexed by their index number. */
- protected static Hashtable _all_by_index = new Hashtable();
-
- /** Lookup a non terminal by index. */
- public static non_terminal find(int indx)
- {
- Integer the_indx = new Integer(indx);
-
- return (non_terminal)_all_by_index.get(the_indx);
- }
-
- /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
-
- /** Total number of non-terminals. */
- public static int number() {return _all.size();}
-
- /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
-
- /** Static counter to assign unique indexes. */
- protected static int next_index = 0;
-
- /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
-
- /** Static counter for creating unique non-terminal names */
- static protected int next_nt = 0;
-
- /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
-
- /** special non-terminal for start symbol */
- public static final non_terminal START_nt = new non_terminal("$START");
-
- /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
-
- /** flag non-terminals created to embed action productions */
- public boolean is_embedded_action = false; /* added 24-Mar-1998, CSA */
-
- /*-----------------------------------------------------------*/
- /*--- Static Methods ----------------------------------------*/
- /*-----------------------------------------------------------*/
-
- /** Method for creating a new uniquely named hidden non-terminal using
- * the given string as a base for the name (or "NT$" if null is passed).
- * @param prefix base name to construct unique name from.
- */
- static non_terminal create_new(String prefix) throws internal_error
- {
- if (prefix == null) prefix = "NT$";
- return new non_terminal(prefix + next_nt++);
- }
-
- /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
-
- /** static routine for creating a new uniquely named hidden non-terminal */
- static non_terminal create_new() throws internal_error
- {
- return create_new(null);
- }
-
- /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
-
- /** Compute nullability of all non-terminals. */
- public static void compute_nullability() throws internal_error
- {
- boolean change = true;
- non_terminal nt;
- Enumeration e;
- production prod;
-
- /* repeat this process until there is no change */
- while (change)
- {
- /* look for a new change */
- change = false;
-
- /* consider each non-terminal */
- for (e=all(); e.hasMoreElements(); )
- {
- nt = (non_terminal)e.nextElement();
-
- /* only look at things that aren't already marked nullable */
- if (!nt.nullable())
- {
- if (nt.looks_nullable())
- {
- nt._nullable = true;
- change = true;
- }
- }
- }
- }
-
- /* do one last pass over the productions to finalize all of them */
- for (e=production.all(); e.hasMoreElements(); )
- {
- prod = (production)e.nextElement();
- prod.set_nullable(prod.check_nullable());
- }
- }
-
- /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
-
- /** Compute first sets for all non-terminals. This assumes nullability has
- * already computed.
- */
- public static void compute_first_sets() throws internal_error
- {
- boolean change = true;
- Enumeration n;
- Enumeration p;
- non_terminal nt;
- production prod;
- terminal_set prod_first;
-
- /* repeat this process until we have no change */
- while (change)
- {
- /* look for a new change */
- change = false;
-
- /* consider each non-terminal */
- for (n = all(); n.hasMoreElements(); )
- {
- nt = (non_terminal)n.nextElement();
-
- /* consider every production of that non terminal */
- for (p = nt.productions(); p.hasMoreElements(); )
- {
- prod = (production)p.nextElement();
-
- /* get the updated first of that production */
- prod_first = prod.check_first_set();
-
- /* if this going to add anything, add it */
- if (!prod_first.is_subset_of(nt._first_set))
- {
- change = true;
- nt._first_set.add(prod_first);
- }
- }
- }
- }
- }
-
- /*-----------------------------------------------------------*/
- /*--- (Access to) Instance Variables ------------------------*/
- /*-----------------------------------------------------------*/
-
- /** Table of all productions with this non terminal on the LHS. */
- protected Hashtable _productions = new Hashtable(11);
-
- /** Access to productions with this non terminal on the LHS. */
- public Enumeration productions() {return _productions.elements();}
-
- /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
-
- /** Total number of productions with this non terminal on the LHS. */
- public int num_productions() {return _productions.size();}
-
- /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
-
- /** Add a production to our set of productions. */
- public void add_production(production prod) throws internal_error
- {
- /* catch improper productions */
- if (prod == null || prod.lhs() == null || prod.lhs().the_symbol() != this)
- throw new internal_error(
- "Attempt to add invalid production to non terminal production table");
-
- /* add it to the table, keyed with itself */
- _productions.put(prod,prod);
- }
-
- /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
-
- /** Nullability of this non terminal. */
- protected boolean _nullable;
-
- /** Nullability of this non terminal. */
- public boolean nullable() {return _nullable;}
-
- /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
-
- /** First set for this non-terminal. */
- protected terminal_set _first_set = new terminal_set();
-
- /** First set for this non-terminal. */
- public terminal_set first_set() {return _first_set;}
-
- /*-----------------------------------------------------------*/
- /*--- General Methods ---------------------------------------*/
- /*-----------------------------------------------------------*/
-
- /** Indicate that this symbol is a non-terminal. */
- public boolean is_non_term()
- {
- return true;
- }
-
- /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
-
- /** Test to see if this non terminal currently looks nullable. */
- protected boolean looks_nullable() throws internal_error
- {
- /* look and see if any of the productions now look nullable */
- for (Enumeration e = productions(); e.hasMoreElements(); )
- /* if the production can go to empty, we are nullable */
- if (((production)e.nextElement()).check_nullable())
- return true;
-
- /* none of the productions can go to empty, so we are not nullable */
- return false;
- }
-
- /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
-
- /** convert to string */
- public String toString()
- {
- return super.toString() + "[" + index() + "]" + (nullable() ? "*" : "");
- }
-
- /*-----------------------------------------------------------*/
-}
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