public static Either <string, AddressBook> AddWorkflow(this AddressBook addressBook,
Func <Contact, Either <string, Contact> > sendMailFunction, Contact contact)
=> Right(addressBook)
.Bind(x => x.AddOrUpdateContactOpt(contact))
.Bind(x => x.SendConfirmationMailOpt(sendMailFunction, contact));
// DON'T INJECT AN IMAILER!! No IoC!! Use a function!!
//
// public static Func<IMailer, Contact, AddressBook, Either<string, AddressBook>> SendConfirmationMail
// = (mailer, contact, addressBook)
// => mailer.Send(contact)
// .Match<Either<string, AddressBook>>(
// errorMsg => Left(errorMsg),
// _ => Right(addressBook));
public static Either <string, AddressBook> SendConfirmationMailOpt(this AddressBook addressBook,
Func <Contact, Either <string, Contact> > sendMailTo, Contact contact)
=> sendMailTo(contact)
.Match <Either <string, AddressBook> >(
errorMsg => Left(errorMsg),
_ => Right(addressBook));