X-Git-Url: http://git.megacz.com/?p=sbp.git;a=blobdiff_plain;f=src%2Fedu%2Fberkeley%2Fsbp%2FUnion.java;h=c1642627c0dac9d744973d40a0c904f7369ceea4;hp=4595ebbec869a88a4ccbc9d1192313a8caf03c30;hb=dc9bb3a45ed306e2e35549076842b3e74efecb48;hpb=03f91bd299c8c8724fe966f527b7410d2cea675d

diff --git a/src/edu/berkeley/sbp/Union.java b/src/edu/berkeley/sbp/Union.java
index 4595ebb..c164262 100644
--- a/src/edu/berkeley/sbp/Union.java
+++ b/src/edu/berkeley/sbp/Union.java
@@ -1,3 +1,5 @@
+// Copyright 2006 all rights reserved; see LICENSE file for BSD-style license
+
 package edu.berkeley.sbp;
 import edu.berkeley.sbp.util.*;
 import edu.berkeley.sbp.*;
@@ -7,75 +9,101 @@ 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); }
+    public Union(String name, Sequence s) { this(name, s, false); }
+    public Union(String name, Sequence s, boolean synthetic) { this(name, synthetic); add(s); }
+
     /**
      *  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() { this(null, false); }
-    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) {
+    public Union add(Sequence s) {
+        if (viewed)
+            throw new RuntimeException("once Union.contains() or Union.iterator() has been invoked, "+
+                                       "you may not add any more Sequences to it\n  "+
+                                       "  union in question: " + this);
+        if (s.needed_or_hated)
+            throw new RuntimeException("you may not add a conjunct directly to a Union");
+        s.in_a_union = true;
+        if (alternatives.contains(s)) return this;
         alternatives.add(s);
-
-        // FIXME: does this make sense?
-        for(Sequence n : s.needs) add(n);
-        for(Sequence n : s.hates) add(n);
+        return this;
     }
 
-    // Epsilon Form //////////////////////////////////////////////////////////////////////////////
-
-    // FIXME
-    public static Union epsilon = new Union("()");
-    static { epsilon.add(Sequence.empty); }
+    /** adds a one-element sequence */
+    public void add(Element e) {
+        add(Sequence.create(e));
+    }
 
-    // FIXME
-    private Forest.Ref epsilonForm = null;
-    Forest epsilonForm() {
-        if (epsilonForm != null) return epsilonForm;
-        epsilonForm = new Forest.Ref();
-        for(Sequence s : this) {
-            // FIXME FIXME FIXME
-            if (new Walk.Cache().possiblyEpsilon(s))
-                epsilonForm.merge(s.epsilonForm());
-        }
+    /** the Forest which results from matching this Union against the empty string at region <tt>region</tt> */
+    Forest epsilonForm(Input.Region region, Cache cache) {
+        viewed = true;
+        Forest.Many epsilonForm = new Forest.Many();
+        for(Sequence s : this)
+            if (cache.possiblyEpsilon(s))
+                epsilonForm.merge(s.epsilonForm(region, cache));
         return epsilonForm;
     }
 
+
     // Display //////////////////////////////////////////////////////////////////////////////
 
-    public String getName() {
-        if (shortForm != null) return shortForm;
-        return "(anon_union)";
-    }
+    boolean isSynthetic() { return synthetic; }
+    String getName()      { return name==null ? "(anon_union)" : name; }
+
     public String toString() {
-        if (shortForm != null) return shortForm;
+        // technically this should be turned on, but we don't make a big deal
+        //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) {
+        // technically this should be turned on, but we don't make a big deal
+        //viewed = true;
         if (synthetic) return sb;
         boolean first = true;
         String before = StringUtil.pad(15, getName()) + " = ";
@@ -91,9 +119,9 @@ public class Union extends Element implements Iterable<Sequence> {
     }
     
     private void bodyToString(StringBuffer sb, String before, String between) {
+        viewed = true;
         boolean first = true;
         for(Sequence s : this) {
-            if (s.lame) continue;
             // FIXME: what to do here about printing out negated sequences?
             sb.append(first ? before : between);
             first = false;