Validation <PhoneNumber> CreateValidPhoneNumberM
(string typeStr, string countryStr, string numberStr)
=> from type in validNumberType(typeStr)
from country in validCountryCode(countryStr)
from number in validNumber(numberStr)
select PhoneNumber.Create(type, country, number);
// monadic with LINQ
Option <PhoneNumber> CreatePhoneNumber_LINQ
(string typeStr, string countryStr, string numberStr)
=> from country in optCountryCode(countryStr)
from type in optNumberType(typeStr)
from number in PhoneNumber.Number.Create(numberStr)
select PhoneNumber.Create(type, country, number);
