Domain Modeling Made Functional

Implementing the Validation Step

We can now start implementing the validation step. The validation step will take the unvalidated order, with all its primitive fields, and transform it into a proper, fully validated domain object.

We modeled the function types for this step like this:

type CheckAddressExists =
  UnvalidatedAddress -> AsyncResult<CheckedAddress,AddressValidationError>

type ValidateOrder =
  CheckProductCodeExists    // dependency
    -> CheckAddressExists   // AsyncResult dependency
    -> UnvalidatedOrder     // input
    -> AsyncResult<ValidatedOrder,ValidationError list>  // output

As we said, we’re going to eliminate the effects for this chapter, so we can remove the AsyncResult parts, leaving us with this:

type CheckAddressExists ...