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() { 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); }
+ 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.Many epsilonForm = null;
return epsilonForm;
}
+
// Display //////////////////////////////////////////////////////////////////////////////
public String getName() {
- if (shortForm != null) return shortForm;
+ if (name != null) return name;
return "(anon_union)";
}
public String toString() {
- if (shortForm != null) return shortForm;
+ 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()) + " = ";
}
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;