X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=src%2Fedu%2Fberkeley%2Fsbp%2FElement.java;h=896540e904f0868bfe1dd4f68ee3fa630ecde6b9;hb=23091054a6842031d168c2628216c2310149cc5d;hp=7be02af6673d58f56b7dae630bfc5e5a3f51b60a;hpb=1a249057cbfd2180910e46672eafee3af46ae470;p=sbp.git

diff --git a/src/edu/berkeley/sbp/Element.java b/src/edu/berkeley/sbp/Element.java
index 7be02af..896540e 100644
--- a/src/edu/berkeley/sbp/Element.java
+++ b/src/edu/berkeley/sbp/Element.java
@@ -10,13 +10,12 @@ import java.lang.ref.*;
 /** the root superclass for all components of the grammar (terminals, nonterminals, literals, etc) */
 public abstract class Element {
 
-    /** if this element always matches exactly one token, return a topology covering exactly those possible tokens, otherwise <tt>null</tt> */
-    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;
-    }
+    /** sorry, you can't make up new, custom elements */
+    Element() { }
+
+    abstract StringBuffer toString(StringBuffer sb);
+
+    /** returns the Forest resulting from matching this element against the empty string */
+    Forest epsilonForm() { throw new Error("element " + this + " has no epsilon form"); }
+
 }