- /** 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;
- }
+ 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"); }
+