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) {
35 for(Sequence n : s.needs) add(n);
36 for(Sequence n : s.hates) add(n);
37 if (/*!synthetic &&*/ shortForm!=null
38 //&& Character.isUpperCase(shortForm.charAt(0))
40 s.setName(toString());
44 * Since every cycle in a non-degenerate grammar contains at
45 * least one Union, every instance of this class must be able to
46 * display itself in both "long form" (list of the long forms of
47 * its alternatives) and "short form" (some abbreviation).
49 * @param shortForm the "short form" display; usually
50 * @param synthetic if true, this Union's "long form" is "obvious" and should not be displayed when printing the grammar
52 public Union(String shortForm) { this(shortForm, false); }
53 public Union(String shortForm, boolean synthetic) {
54 this.shortForm = shortForm;
55 this.synthetic = synthetic;
58 public static Union epsilon = new Union("()");
59 static { epsilon.add(Sequence.empty); }
61 private Forest.Ref epsilonForm = null;
62 Forest epsilonForm() {
63 if (epsilonForm != null) return epsilonForm;
64 epsilonForm = new Forest.Ref();
65 for(Sequence s : this)
66 if (s.possiblyEpsilon(null))
67 epsilonForm.merge(s.epsilonForm());
71 // Display //////////////////////////////////////////////////////////////////////////////
73 public String toString() { return shortForm; }
74 private static String pad(int i,String s) { return s.length() >= i ? s : pad(i-1,s)+" "; }
75 public void toString(StringBuffer sb) {
76 if (synthetic) return;
78 if (alternatives.size()==0) {
79 sb.append(pad(15, shortForm) + "::= ");
80 } else for(Sequence s : this) {
81 sb.append(pad(15, first ? shortForm : "") + (first ? "::= " : " | "));
83 sb.append(s.toString());
89 // SubUnion //////////////////////////////////////////////////////////////////////////////
91 /** FIXME this is kind of a hack */
92 public class Subset extends Union {
93 private final Set<Sequence> exclude;
94 public Subset(String shortForm, Set<Sequence> exclude) { super(shortForm, true); this.exclude = exclude; }
95 public Iterator<Sequence> iterator() {
96 final Iterator<Sequence> it = Union.this.iterator();
97 return new Iterator<Sequence>() {
98 private Sequence next = it.hasNext() ? it.next() : null;
99 public boolean hasNext() { return next != null; }
100 public Sequence next() {
103 next = it.hasNext() ? it.next() : null;
104 } while (next != null && (next instanceof Sequence) && exclude.contains((Sequence)next));
107 public void remove() { throw new Error(); }