convered maximal to use character lookahead

[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..db0db7d 100644 (file)
--- a/src/edu/berkeley/sbp/Union.java
+++ b/src/edu/berkeley/sbp/Union.java
@@ -19,13 +19,14 @@ public class Union extends Element implements Iterable<Sequence> {
     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();
             if (ret==null) ret = a.dup();
-            else           ret.add(a.dup());
+            else           ret = ret.union(a.dup());
         }
+        if (ret==null) throw new RuntimeException("confusion on " + this);
         return ret;
     }