private Filter translateOr(Or filter) throws IllegalFilterException {
if (!(filter instanceof Or)) {
return filter;
}
// a|b == ~~(a|b) negative introduction
// ~(a|b) == (~a + ~b) modus ponens
// ~~(a|b) == ~(~a + ~b) substitution
// a|b == ~(~a + ~b) negative simpilification
Iterator i = filter.getChildren().iterator();
List translated = new ArrayList();
while (i.hasNext()) {
Filter f = (Filter) i.next();
if (f instanceof Not) {
// simplify it
Not logic = (Not) f;
Filter next = logic.getFilter();
translated.add(next);
} else {
translated.add(ff.not(f));
}
}
Filter and = ff.and(translated);
return ff.not(and);
}
public Object visit(Not filter, Object extraData) {
if (filter.getFilter() instanceof Not) {
// simplify out double negation
Not inner = (Not) filter.getFilter();
return inner.getFilter().accept(this, extraData);
} else {
return super.visit(filter, extraData);
}
}
@Override
public Object visit(Not filter, Object extraData) {
StringWriter output = asStringWriter(extraData);
output.append("NOT (");
filter.getFilter().accept(this, output);
output.append(")");
return output;
}