X-Git-Url: http://git.megacz.com/?p=sbp.git;a=blobdiff_plain;f=src%2Fedu%2Fberkeley%2Fsbp%2FUnion.java;h=a7a76302455b8e9c051224abd3fe022a2a828bb8;hp=df6c374af8399d98168f3282f5f859580e8eb34b;hb=87f214f3da9f43c3ab93923313845c372f9a96be;hpb=0a0227b9180534d2a431f3d6e08a398bde2244c4

diff --git a/src/edu/berkeley/sbp/Union.java b/src/edu/berkeley/sbp/Union.java
index df6c374..a7a7630 100644
--- a/src/edu/berkeley/sbp/Union.java
+++ b/src/edu/berkeley/sbp/Union.java
@@ -18,6 +18,18 @@ 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) 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 (a==null) continue;
+            if (ret==null) ret = a.dup();
+            else           ret.add(a.dup());
+        }
+        return ret;
+    }
+
     /** adds an alternative */
     public void add(Sequence s) { alternatives.add(s); }
 
@@ -36,6 +48,9 @@ public class Union extends Element implements Iterable<Sequence> {
         this.synthetic = synthetic;
     }
 
+    public static Union epsilon = new Union("()");
+    static { epsilon.add(Sequence.empty); }
+
     private Forest.Ref epsilonForm = null;
     Forest epsilonForm() {
         if (epsilonForm != null) return epsilonForm;
@@ -50,7 +65,7 @@ public class Union extends Element implements Iterable<Sequence> {
 
     public String toString() { return shortForm; }
     private static String pad(int i,String s) { return s.length() >= i ? s : pad(i-1,s)+" "; }
-    void toString(StringBuffer sb) {
+    public void toString(StringBuffer sb) {
         if (synthetic) return;
         boolean first = true;
         if (alternatives.size()==0) {