+// (C) 2006-2007 all rights reserved; see LICENSE file for BSD-style license
+
package edu.berkeley.sbp;
-import edu.berkeley.sbp.util.*;
-import edu.berkeley.sbp.*;
-import edu.berkeley.sbp.*;
-import java.io.*;
import java.util.*;
-import java.lang.reflect.*;
-import java.lang.ref.*;
-/** the root superclass for all components of the grammar (terminals, nonterminals, literals, etc) */
-public abstract class Element {
+/**
+ * <font color=green>
+ * the root superclass for all components of the grammar (terminals,
+ * nonterminals, literals, etc)
+ * </font>
+ */
+public abstract class Element implements SequenceOrElement {
+
+ /** sorry, you can't make up new, custom elements */
+ Element() { }
+
+ /** a more verbose version of toString() for displaying whole grammars */
+ abstract StringBuffer toString(StringBuffer sb);
- /** if this element always matches exactly one token, return a topology covering exactly those possible tokens, otherwise <tt>null</tt> */
- abstract Topology toAtom();
- public Topology toAtom0() { return toAtom(); }
- Forest epsilonForm() { throw new Error("no epsilon form: " + this); }
- final boolean possiblyEpsilon(Walk.Cache cache) {
- Boolean ret = cache==null ? null : cache.possiblyEpsilon.get(this);
- if (ret != null) return ret.booleanValue();
- ret = new Walk.PossiblyEpsilon().walk(this) ? Boolean.TRUE : Boolean.FALSE;
- if (cache != null) cache.possiblyEpsilon.put(this, ret);
- return ret;
- }
}