-// Copyright 2006 all rights reserved; see LICENSE file for BSD-style license
+// (C) 2006-2007 all rights reserved; see LICENSE file for BSD-style license
package edu.berkeley.sbp;
-import edu.berkeley.sbp.util.*;
-import edu.berkeley.sbp.*;
-import edu.berkeley.sbp.*;
-import java.io.*;
import java.util.*;
-import java.lang.reflect.*;
-import java.lang.ref.*;
-/** <font color=green>the root superclass for all components of the grammar (terminals, nonterminals, literals, etc)</font> */
+/**
+ * <font color=green>
+ * the root superclass for all components of the grammar (terminals,
+ * nonterminals, literals, etc)
+ * </font>
+ */
public abstract class Element implements SequenceOrElement {
/** sorry, you can't make up new, custom elements */
Element() { }
+ /** a more verbose version of toString() for displaying whole grammars */
abstract StringBuffer toString(StringBuffer sb);
- /** returns the Forest resulting from matching this element against the empty string */
- Forest<?> epsilonForm(Input.Region loc) { throw new Error("element " + this + " has no epsilon form"); }
-
+ /** a slow and inefficient epsilon-ness checker used when constructing parse trees (see Union.epsilonForm()) */
+ public static boolean possiblyEpsilon(SequenceOrElement e) {
+ if (e instanceof Atom) return false;
+ if (e instanceof Sequence) {
+ Sequence s = (Sequence)e;
+ for(Sequence.Pos p = s.firstp(); !p.isLast(); p = p.next())
+ if (!possiblyEpsilon(p.element()))
+ return false;
+ return true;
+ }
+ if (e instanceof Union) {
+ Union u = (Union)e;
+ if (u.visiting) return true;
+ try {
+ u.visiting = true;
+ for(Sequence s : u)
+ if (possiblyEpsilon(s))
+ return true;
+ return false;
+ } finally {
+ u.visiting = false;
+ }
+ }
+ throw new Error();
+ }
+ boolean visiting = false;
}