/// <summary>
/// For a simple yes/no question where 'y' is true
/// </summary>
public static Validator <bool> Bool()
{
return(response => Regex.IsMatch(response, "^(y|n|yes|no)$", RegexOptions.IgnoreCase) ?
Validated <bool> .Success(response.StartsWith("y", StringComparison.OrdinalIgnoreCase)) :
Validated <bool> .Error("Please enter 'y' or 'n'."));
}