revealing-way-2.kt

fun validateEmailAddress(value: String): EmailAddress {
    // does some validation and
    // if the validation fails it returns InvalidEmailAddress
    // otherwise a ValidEmailAddress
}

fun validatePassword(emailAddress: ValidEmailAddress, password: String): Password {
    // does some validation against the valid email address
    // if the validation fails it returns an InvalidPassword
    // otherwise a ValidPassword
}

fun requestToken(emailAddress: ValidEmailAddress, password: ValidPassword): Token {
    // having only valid values makes the code simple
    // just make the request and return the token
    return Token("some kind of token")
}