X-Git-Url: http://git.megacz.com/?p=sbp.git;a=blobdiff_plain;f=src%2Fedu%2Fberkeley%2Fsbp%2FElement.java;h=a37e96036d65206b6be4f5e56c9970ef168f2d0b;hp=33bfd8d7d08f5027e136aef1eaff959dfbf92ce7;hb=f069d11a0bc59d63b078df8a4aa488498c4e9cc2;hpb=5d18f5606c9296e6b0c5749f05fc68f358ace2f6
diff --git a/src/edu/berkeley/sbp/Element.java b/src/edu/berkeley/sbp/Element.java
index 33bfd8d..a37e960 100644
--- a/src/edu/berkeley/sbp/Element.java
+++ b/src/edu/berkeley/sbp/Element.java
@@ -1,18 +1,46 @@
+// (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.*;
-/** 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 {
- abstract StringBuffer toString(StringBuffer sb);
+ /** sorry, you can't make up new, custom elements */
+ Element() { }
- /** if this element always matches exactly one token, return a topology covering exactly those possible tokens, otherwise null */
- Forest epsilonForm() { return null; }
+ /** a more verbose version of toString() for displaying whole grammars */
+ abstract StringBuffer toString(StringBuffer sb);
+ /** 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;
}