+// Copyright 2006 all rights reserved; see LICENSE file for BSD-style license
+
package edu.berkeley.sbp;
import java.io.*;
import java.util.*;
import edu.berkeley.sbp.*;
import edu.berkeley.sbp.*;
-/** <font color=green>an element which matches exactly one input token</font> */
-public abstract class Atom<T> extends Element implements Topology<Atom<T>> {
+/**
+ * <font color=green>an element which matches some set of one-token-long input strings</font>.
+ *
+ * <p>
+ * This class is a topology over itself (yes, that's sort of <a
+ * href=http://en.wikipedia.org/wiki/Frege>Frege'd</a> up) so that
+ * Atoms can be intersected and unioned with each other to result in
+ * other Atom<Token>'s (rather than raw Topology<Token>'s, which are
+ * not Elements). If you want the latter, use the getTokenTopology()
+ * method.
+ * </p>
+ */
+public abstract class Atom<Token> extends Element implements Topology<Atom<Token>> {
+
+ /** the set (topology) of tokens that can match this element */
+ public abstract Topology<Token> getTokenTopology();
- public abstract Topology<T> underlying();
- public abstract String toString();
- public StringBuffer toString(StringBuffer sb) { sb.append(this); return sb; }
+ StringBuffer toString(StringBuffer sb) { sb.append(this); return sb; }
}
+