@Override
public ValueSource parse(FunctionQParser fp) throws SyntaxError {
String key = fp.parseArg();
double val = fp.parseDouble();
AtomicInteger counter = new AtomicInteger();
if (null != counters.putIfAbsent(key, counter)) {
throw new IllegalArgumentException("Key has already been used: " + key);
}
return new CountDocsValueSource(counter, val);
}
