/**
* Checks if the specified expression yields a double. Returns the double or throws an exception.
*
* @param e expression to be checked
* @param ctx query context
* @return double
* @throws QueryException query exception
*/
public final double checkDbl(final Expr e, final QueryContext ctx) throws QueryException {
final Item it = checkNoEmpty(e.item(ctx, input), AtomType.DBL);
if (!it.unt() && !it.num()) Err.number(this, it);
return it.dbl(input);
}
