+// 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.*;
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>();
+ private final String name;
+ private final boolean synthetic;
+ private boolean viewed = false;
- public Iterator<Sequence> iterator() { return alternatives.iterator(); }
- public boolean contains(Sequence s) { return alternatives.contains(s); }
+ private final List<Sequence> alternatives = new ArrayList<Sequence>();
- 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;
- else ret = ret.union(a);
- }
- if (ret==null) throw new RuntimeException("confusion on " + this);
- return ret;
- }
-
- /** adds an alternative */
- public void add(Sequence s) {
- alternatives.add(s);
- for(Sequence n : s.needs) add(n);
- for(Sequence n : s.hates) add(n);
- if (/*!synthetic &&*/ shortForm!=null
- //&& Character.isUpperCase(shortForm.charAt(0))
- )
- s.setName(toString());
- }
+ 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(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 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);
+ return this;
+ }
+
+ /** adds a one-element sequence */
+ public void add(Element e) {
+ add(Sequence.create(e));
+ }
- private Forest.Ref epsilonForm = null;
- Forest epsilonForm() {
- if (epsilonForm != null) return epsilonForm;
- epsilonForm = new Forest.Ref();
+ /** 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 (s.possiblyEpsilon(null))
- epsilonForm.merge(s.epsilonForm());
+ if (cache.possiblyEpsilon(s))
+ epsilonForm.merge(s.epsilonForm(region, cache));
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;
+ boolean isSynthetic() { return synthetic; }
+ String getName() { return name==null ? "(anon_union)" : name; }
+
+ public String toString() {
+ // 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()) + " = ";
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());
}
}
projects / sbp.git / blobdiff