Domain Modeling Made Functional

Are Dependencies Part of the Design?

In the code above, we have treated calls to other contexts (such as CheckProductCodeExists and ValidateAddress) as dependencies to be documented. Our design for each substep added explicit extra parameters for these dependencies:

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

type PriceOrder =
  GetProductPrice                        // explicit dependency
    -> ValidatedOrder                    // input
    -> Result<PricedOrder,PricingError>  // output

You might argue that how any process performs its job should be hidden from us. Do we really care about what systems ...