Domain Modeling Made Functional

Modeling Complex Data

When we documented our domain, we used AND and OR to represent more complex models. In Chapter 4, ​Understanding Types​, we learned about F#’s algebraic type system and saw that it also used AND and OR to create complex types from simple ones.

Let’s now take the obvious step and use the algebraic type system to model our domain.

Modeling with Record Types

In our domain, we saw that many data structures were built from AND relationships. For example, our original, simple Order was defined like this:

data Order =
    CustomerInfo
    AND ShippingAddress
    AND BillingAddress
    AND list of OrderLines
    AND AmountToBill

This translates directly to an F# record structure, like this:

type Order = {
 CustomerInfo : CustomerInfo ...