X-Git-Url: http://git.megacz.com/?p=sbp.git;a=blobdiff_plain;f=src%2Fedu%2Fberkeley%2Fsbp%2FUnion.java;h=77a158181a309578ca9e6354ca54db520370d0d6;hp=db0db7dca1a322625895ee88f6d338a7934623ba;hb=75d0fa39d405292f4b831a6d1743f2aeea01ebd4;hpb=0516ea34996c86664928ef948013b749876b87ec

diff --git a/src/edu/berkeley/sbp/Union.java b/src/edu/berkeley/sbp/Union.java
index db0db7d..77a1581 100644
--- a/src/edu/berkeley/sbp/Union.java
+++ b/src/edu/berkeley/sbp/Union.java
@@ -7,98 +7,115 @@ 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> {
 
-    final String shortForm;
-    final boolean synthetic;
-    private final List<Sequence> alternatives = new ArrayList<Sequence>();
-
-    public Iterator<Sequence> iterator() { return alternatives.iterator(); }
+    private final String name;
+    private final boolean synthetic;
+    private boolean viewed = false;
 
-    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 (ret==null) ret = a.dup();
-            else           ret = ret.union(a.dup());
-        }
-        if (ret==null) throw new RuntimeException("confusion on " + this);
-        return ret;
-    }
+    private final List<Sequence> alternatives = new ArrayList<Sequence>();
 
-    /** adds an alternative */
-    public void add(Sequence s) { alternatives.add(s); }
+    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;
     }
 
-    public static Union epsilon = new Union("()");
-    static { epsilon.add(Sequence.empty); }
+    public boolean contains(Sequence s) {
+        viewed = true;
+        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);
+    }
+
 
-    private Forest.Ref epsilonForm = null;
+    // Epsilon Form //////////////////////////////////////////////////////////////////////////////
+
+    // FIXME
+    private Forest.Many epsilonForm = null;
     Forest epsilonForm() {
         if (epsilonForm != null) return epsilonForm;
-        epsilonForm = new Forest.Ref();
-        for(Sequence s : this)
-            if (s.possiblyEpsilon(null))
+        epsilonForm = new Forest.Many();
+        for(Sequence s : this) {
+            // FIXME FIXME FIXME
+            if (new Walk.Cache().possiblyEpsilon(s))
                 epsilonForm.merge(s.epsilonForm());
+        }
         return epsilonForm;
     }
 
+
     // Display //////////////////////////////////////////////////////////////////////////////
 
-    public String toString() { return shortForm; }
-    private static String pad(int i,String s) { return s.length() >= i ? s : pad(i-1,s)+" "; }
-    public void toString(StringBuffer sb) {
-        if (synthetic) return;
+    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(pad(15, shortForm) + "::= ");
-        } else for(Sequence s : this) {
-            sb.append(pad(15, first ? shortForm : "") + (first ? "::= " : "  | "));
-            first = false;
-            sb.append(s.toString());
+            sb.append(before);
+        } else {
+            bodyToString(sb,
+                         before,
+                         "\n" + StringUtil.pad(15, "")        + " | ");
             sb.append('\n');
         }
-        sb.append('\n');
+        return sb;
     }
-
-    // SubUnion //////////////////////////////////////////////////////////////////////////////
-
-    /** FIXME this is kind of a hack */
-    public class Subset extends Union {
-        private final Set<Sequence> exclude;
-        public Subset(String shortForm, Set<Sequence> exclude) { super(shortForm, true); this.exclude = exclude; }
-        public Iterator<Sequence> iterator() {
-            final Iterator<Sequence> it = Union.this.iterator();
-            return new Iterator<Sequence>() {
-                private Sequence next = it.hasNext() ? it.next() : null;
-                public boolean hasNext() { return next != null; }
-                public Sequence next() {
-                    Sequence ret = next;
-                    do {
-                        next = it.hasNext() ? it.next() : null;
-                    } while (next != null && (next instanceof Sequence) && exclude.contains((Sequence)next));
-                    return ret;
-                }
-                public void remove() { throw new Error(); }
-            };
+    
+    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(first ? before : between);
+            first = false;
+            sb.append(s.toString());
         }
     }