01: package gnu.expr;
02:
03: import gnu.mapping.*;
04:
05: import java.io.PrintWriter;
06:
07: public class Undefined extends Object implements Printable {
08: static private Undefined undef = null;
09:
10: static public Undefined getInstance() {
11: if (undef == null)
12: undef = new Undefined();
13: return undef;
14: }
15:
16: public Undefined() {
17: }
18:
19: public void print(java.io.PrintWriter ps) {
20: ps.print("#<undefined>");
21: }
22: }
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