1 package edu.berkeley.sbp;
2 import edu.berkeley.sbp.util.*;
3 import edu.berkeley.sbp.*;
4 import edu.berkeley.sbp.*;
7 import java.lang.reflect.*;
8 import java.lang.ref.*;
10 /** an element which can produce one of several alternatives */
11 public class Union extends Element implements Iterable<Sequence> {
13 final String shortForm;
14 final boolean synthetic;
15 private final List<Sequence> alternatives = new ArrayList<Sequence>();
17 public Iterator<Sequence> iterator() { return alternatives.iterator(); }
18 public boolean contains(Sequence s) { return alternatives.contains(s); }
21 if (alternatives.size()==0) throw new RuntimeException("cannot build an Atom from a Union with no productions");
23 for(Sequence s : this) {
24 Topology a = s.toAtom();
25 if (ret==null) ret = a;
26 else ret = ret.union(a);
28 if (ret==null) throw new RuntimeException("confusion on " + this);
32 /** adds an alternative */
33 public void add(Sequence s) { alternatives.add(s); }
36 * Since every cycle in a non-degenerate grammar contains at
37 * least one Union, every instance of this class must be able to
38 * display itself in both "long form" (list of the long forms of
39 * its alternatives) and "short form" (some abbreviation).
41 * @param shortForm the "short form" display; usually
42 * @param synthetic if true, this Union's "long form" is "obvious" and should not be displayed when printing the grammar
44 public Union(String shortForm) { this(shortForm, false); }
45 public Union(String shortForm, boolean synthetic) {
46 this.shortForm = shortForm;
47 this.synthetic = synthetic;
50 public static Union epsilon = new Union("()");
51 static { epsilon.add(Sequence.empty); }
53 private Forest.Ref epsilonForm = null;
54 Forest epsilonForm() {
55 if (epsilonForm != null) return epsilonForm;
56 epsilonForm = new Forest.Ref();
57 for(Sequence s : this)
58 if (s.possiblyEpsilon(null))
59 epsilonForm.merge(s.epsilonForm());
63 // Display //////////////////////////////////////////////////////////////////////////////
65 public String toString() { return shortForm; }
66 private static String pad(int i,String s) { return s.length() >= i ? s : pad(i-1,s)+" "; }
67 public void toString(StringBuffer sb) {
68 if (synthetic) return;
70 if (alternatives.size()==0) {
71 sb.append(pad(15, shortForm) + "::= ");
72 } else for(Sequence s : this) {
73 sb.append(pad(15, first ? shortForm : "") + (first ? "::= " : " | "));
75 sb.append(s.toString());
81 // SubUnion //////////////////////////////////////////////////////////////////////////////
83 /** FIXME this is kind of a hack */
84 public class Subset extends Union {
85 private final Set<Sequence> exclude;
86 public Subset(String shortForm, Set<Sequence> exclude) { super(shortForm, true); this.exclude = exclude; }
87 public Iterator<Sequence> iterator() {
88 final Iterator<Sequence> it = Union.this.iterator();
89 return new Iterator<Sequence>() {
90 private Sequence next = it.hasNext() ? it.next() : null;
91 public boolean hasNext() { return next != null; }
92 public Sequence next() {
95 next = it.hasNext() ? it.next() : null;
96 } while (next != null && (next instanceof Sequence) && exclude.contains((Sequence)next));
99 public void remove() { throw new Error(); }