/**
* Checks if the specified expression yields a float. Returns the float or throws an exception.
*
* @param ex expression to be evaluated
* @param qc query context
* @return float
* @throws QueryException query exception
*/
protected final float toFloat(final Expr ex, final QueryContext qc) throws QueryException {
final Item it = ex.atomItem(qc, info);
if (checkNoEmpty(it, AtomType.FLT).type.isNumberOrUntyped()) return it.flt(info);
throw numberError(this, it);
}
