X-Git-Url: http://git.megacz.com/?p=sbp.git;a=blobdiff_plain;f=src%2Fedu%2Fberkeley%2Fsbp%2FElement.java;h=4ccde61eb49ecb9cf23c164c9f013cb5c7c8a0ce;hp=f88ce87034116c22d58ac64dff9b5aa7f2f3db3a;hb=75d0fa39d405292f4b831a6d1743f2aeea01ebd4;hpb=9ded11559a1b6f817e99355b1c9e2c88042e91d4
diff --git a/src/edu/berkeley/sbp/Element.java b/src/edu/berkeley/sbp/Element.java
index f88ce87..4ccde61 100644
--- a/src/edu/berkeley/sbp/Element.java
+++ b/src/edu/berkeley/sbp/Element.java
@@ -7,18 +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) */
+/** 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 null */
- 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;
- }
+ /** 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"); }
+
}