X-Git-Url: http://git.megacz.com/?p=sbp.git;a=blobdiff_plain;f=src%2Fedu%2Fberkeley%2Fsbp%2FElement.java;h=35678abfb3cba74d48b7f3eaf830373804a98e76;hp=c94adbdcc6f80a3ed43822c8b632b1fef16dc0b5;hb=5916007808f8deac12025eaf6bf067719ddd1591;hpb=fd97655ce34c3aff1a47bfb2f45775ac711923b1

diff --git a/src/edu/berkeley/sbp/Element.java b/src/edu/berkeley/sbp/Element.java
index c94adbd..35678ab 100644
--- a/src/edu/berkeley/sbp/Element.java
+++ b/src/edu/berkeley/sbp/Element.java
@@ -1,3 +1,5 @@
+// Copyright 2006 all rights reserved; see LICENSE file for BSD-style license
+
 package edu.berkeley.sbp;
 import edu.berkeley.sbp.util.*;
 import edu.berkeley.sbp.*;
@@ -7,18 +9,16 @@ 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() which should show the entire grammar */
+    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();
+    /** returns the Forest resulting from matching this element against the empty string */
+    Forest<?> epsilonForm(Input.Region loc) { throw new Error("element " + this + " has no epsilon form"); }
 
-    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;
-    }
 }