removed illegal use of double-star

[sbp.git] / src / edu / berkeley / sbp / Union.java

diff --git a/src/edu/berkeley/sbp/Union.java b/src/edu/berkeley/sbp/Union.java
index 7274dae..a7a7630 100644 (file)
--- a/src/edu/berkeley/sbp/Union.java
+++ b/src/edu/berkeley/sbp/Union.java
@@ -19,10 +19,11 @@ public class Union extends Element implements Iterable<Sequence> {
     void reachable(HashSet<Sequence.Position> h) { for(Sequence s : alternatives) s.reachable(h); }
 
     Topology toAtom() {
     void reachable(HashSet<Sequence.Position> h) { for(Sequence s : alternatives) s.reachable(h); }
 
     Topology toAtom() {

-        if (alternatives.size()==0) return null;
+        if (alternatives.size()==0) throw new RuntimeException("cannot build an Atom from a Union with no productions");

         Topology ret = null;
         for(Sequence s : this) {
             Topology a = s.toAtom();
         Topology ret = null;
         for(Sequence s : this) {
             Topology a = s.toAtom();

+            if (a==null) continue;

             if (ret==null) ret = a.dup();
             else           ret.add(a.dup());
         }
             if (ret==null) ret = a.dup();
             else           ret.add(a.dup());
         }