X-Git-Url: http://git.megacz.com/?p=sbp.git;a=blobdiff_plain;f=src%2Fedu%2Fberkeley%2Fsbp%2FUnion.java;h=77a158181a309578ca9e6354ca54db520370d0d6;hp=dce9cbec6351ea31480c0ee3a96ea2a59362e565;hb=75d0fa39d405292f4b831a6d1743f2aeea01ebd4;hpb=6b24a8ff6410a47d7290c2b42587fd8a8c5341e8

diff --git a/src/edu/berkeley/sbp/Union.java b/src/edu/berkeley/sbp/Union.java
index dce9cbe..77a1581 100644
--- a/src/edu/berkeley/sbp/Union.java
+++ b/src/edu/berkeley/sbp/Union.java
@@ -7,51 +7,65 @@ import java.util.*;
 import java.lang.reflect.*;
 import java.lang.ref.*;
 
-/** an element which can produce one of several alternatives */
+/**
+ *  <font color=green>an element which can produce one of several alternatives</font>.
+ *  <p>
+ *
+ *  Unlike the other Elements, Union is not immutable once
+ *  constructed.  To simulate this desirable feature, it is immutable
+ *  <i>once examined</i> by taking its iterator or calling contains().
+ */
 public class Union extends Element implements Iterable<Sequence> {
 
+    private final String name;
+    private final boolean synthetic;
+    private boolean viewed = false;
+
+    private final List<Sequence> alternatives = new ArrayList<Sequence>();
+
+    public Union(String name) { this(name, false); }
+
     /**
      *  Since every cycle in a non-degenerate grammar contains at
      *  least one Union, every instance of this class must be able to
      *  display itself in both "long form" (list of the long forms of
-     *  its alternatives) and "short form" (some abbreviation).
+     *  its alternatives) and "short form" (some name).
      *
-     *  @param shortForm the "short form" display; usually 
+     *  @param shortForm the "short form" display; for display purposes only
      *  @param synthetic if true, this Union's "long form" is "obvious" and should not be displayed when printing the grammar
      */
-    public Union(String shortForm) { this(shortForm, false); }
-    public Union(String shortForm, boolean synthetic) {
-        this.shortForm = shortForm;
+    public Union(String name, boolean synthetic) {
+        this.name = name;
         this.synthetic = synthetic;
     }
 
-    final String shortForm;
-    final boolean synthetic;
-    private final List<Sequence> alternatives = new ArrayList<Sequence>();
+    public boolean contains(Sequence s) {
+        viewed = true;
+        return alternatives.contains(s);
+    }
 
-    public Iterator<Sequence> iterator() { return alternatives.iterator(); }
-    public boolean contains(Sequence s) { return alternatives.contains(s); }
+    /** iterator over this Union's Sequences */
+    public Iterator<Sequence> iterator() {
+        viewed = true;
+        return alternatives.iterator();
+    }
 
     /** adds an alternative */
     public void add(Sequence s) {
+        if (viewed)
+            throw new RuntimeException("attempt to add a Sequence to a Union that has already been examined");
+        if (alternatives.contains(s)) return;
         alternatives.add(s);
-
-        // FIXME: does this make sense?
-        for(Sequence n : s.needs) add(n);
-        for(Sequence n : s.hates) add(n);
     }
 
-    // Epsilon Form //////////////////////////////////////////////////////////////////////////////
 
-    // FIXME
-    public static Union epsilon = new Union("()");
-    static { epsilon.add(Sequence.empty); }
+    // Epsilon Form //////////////////////////////////////////////////////////////////////////////
 
     // FIXME
-    private Forest.Ref epsilonForm = null;
+    private Forest.Many epsilonForm = null;
     Forest epsilonForm() {
         if (epsilonForm != null) return epsilonForm;
-        epsilonForm = new Forest.Ref();
+        epsilonForm = new Forest.Many();
         for(Sequence s : this) {
             // FIXME FIXME FIXME
             if (new Walk.Cache().possiblyEpsilon(s))
@@ -60,23 +74,49 @@ public class Union extends Element implements Iterable<Sequence> {
         return epsilonForm;
     }
 
+
     // Display //////////////////////////////////////////////////////////////////////////////
 
-    public String toString() { return shortForm; }
+    public String getName() {
+        if (name != null) return name;
+        return "(anon_union)";
+    }
+    public String toString() {
+        viewed = true;
+        if (name != null) return name;
+        StringBuffer sb = new StringBuffer();
+        sb.append("(");
+        bodyToString(sb, "", " | ");
+        sb.append(")");
+        return sb.toString();
+    }
+
+    /** display this union in long/expanded form */
     public StringBuffer toString(StringBuffer sb) {
+        viewed = true;
         if (synthetic) return sb;
         boolean first = true;
+        String before = StringUtil.pad(15, getName()) + " = ";
         if (alternatives.size()==0) {
-            sb.append(StringUtil.pad(15, shortForm) + " = ");
-        } else for(Sequence s : this) {
+            sb.append(before);
+        } else {
+            bodyToString(sb,
+                         before,
+                         "\n" + StringUtil.pad(15, "")        + " | ");
+            sb.append('\n');
+        }
+        return sb;
+    }
+    
+    private void bodyToString(StringBuffer sb, String before, String between) {
+        viewed = true;
+        boolean first = true;
+        for(Sequence s : this) {
             // FIXME: what to do here about printing out negated sequences?
-            sb.append(StringUtil.pad(15, first ? shortForm : "") + (first ? " = " : "  | "));
+            sb.append(first ? before : between);
             first = false;
             sb.append(s.toString());
-            sb.append('\n');
         }
-        sb.append('\n');
-        return sb;
     }
 
 }