eval method

Implementation

@override
Object? eval(Map<String, Object?> row) {
  if (isAggregate) {
    throw StateError(
      'Aggregate function $name() cannot be evaluated as a scalar',
    );
  }
  final fn = kScalarFunctions[name];
  if (fn == null) {
    throw StateError('Unknown function: $name');
  }
  final values = args.map((a) => a.eval(row)).toList();
  return fn(values);
}