XML — Architecture, Tools, Techniques - Department of Computer ...

TraceN is a top-level nested class in Actor. The TraceN objects show their nonterminal name
qualified with an index.
Now we get new StringBuffer objects all the time and they can be returned as result of
reduce(). The trace shows that this trivially produces a syntax tree:
$ java -classpath .:oops.jar oops.Compile -f Actor expr.ser Scanner
GoalMakerFactory is Actor
3*(4+5)
...
lines1 shift sum2
sum [product [term 3] * [term ( [sum [product [term 4]] + [product [term 5]]] )]]
Arithmetic Expressions in XML
The Element Construction Set contains classes to build a tree and render it in XML. Xml is an
Actor for expr.ebnf. It uses these classes to render arithmetic expressions in XML:
/** convert arithmetic expressions to XML.
*/
public class Xml extends Actor {
%%
lines: ( sum? "\n" )*;
%
return new GoalAdapter() {
public void shift (Goal sender, Object value) {
if (result == null) result = new Root("expr");
((Root)result).add(value);
}
public Object reduce () {
if (result != null)
System.out.println(result);
return null; // no serialized tree to output
}
};
%
sum: product ( "+" product | "-" product )*;
%
return new GoalAdapter() {
public void shift (Goal sender, Object value) {
if (result == null) result = value;
else ((Element)result).add(value);
}
public void shift (Lit sender, Object value) {
if (value.equals("+"))
result = new Element("add", new Object[]{ result });
else result = new Element("sub", new Object[]{ result });
}
};
%
51
oops/Xml.actor