X-Git-Url: http://git.megacz.com/?p=sbp.git;a=blobdiff_plain;f=src%2Fedu%2Fberkeley%2Fsbp%2FSequence.java;h=a5149f2d094ef3dee1b4712f7bc67713eeb9650c;hp=9586f728e1e5df391de200cfd00d1c090b751e2d;hb=87f214f3da9f43c3ab93923313845c372f9a96be;hpb=2690f6c749f117a103c57d651d89f1b4fbf1316d;ds=sidebyside

diff --git a/src/edu/berkeley/sbp/Sequence.java b/src/edu/berkeley/sbp/Sequence.java
index 9586f72..a5149f2 100644
--- a/src/edu/berkeley/sbp/Sequence.java
+++ b/src/edu/berkeley/sbp/Sequence.java
@@ -35,8 +35,11 @@ public abstract class Sequence extends Element implements Iterable<Element> {
 
     ////////////////////////////////////////////////////////////////////////////////
 
+    public Topology noFollow() { return null; }
+
     Topology toAtom() {
-        if (elements.length!=1) return null;
+        if (elements.length>1) throw new RuntimeException("cannot invoke toAtom() on a Sequence with " + elements.length + " elements: " + this);
+        if (elements.length==0) return null;
         return elements[0].toAtom();
     }