X-Git-Url: http://git.megacz.com/?p=sbp.git;a=blobdiff_plain;f=src%2Fedu%2Fberkeley%2Fsbp%2FElement.java;h=16ae2f04e1a874dac968f0c2b65e375cab537387;hp=7be02af6673d58f56b7dae630bfc5e5a3f51b60a;hb=111166986ad83b54d0cae5c03c2304d23e332f29;hpb=1a249057cbfd2180910e46672eafee3af46ae470
diff --git a/src/edu/berkeley/sbp/Element.java b/src/edu/berkeley/sbp/Element.java
index 7be02af..16ae2f0 100644
--- a/src/edu/berkeley/sbp/Element.java
+++ b/src/edu/berkeley/sbp/Element.java
@@ -7,16 +7,15 @@ 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 {
+/** the root superclass for all components of the grammar (terminals, nonterminals, literals, etc) */
+public abstract class Element implements SequenceOrElement {
+
+ /** 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"); }
- /** if this element always matches exactly one token, return a topology covering exactly those possible tokens, otherwise null */
- 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;
- }
}