Domain Modeling Made Functional

Composing the Pipeline Steps Together

Now we’re ready to complete the workflow by composing the implementations of the steps into a pipeline. We want the code to look something like this:

let placeOrder : PlaceOrderWorkflow =
  fun unvalidatedOrder ->
    unvalidatedOrder
    |> validateOrder
    |> priceOrder
    |> acknowledgeOrder
    |> createEvents

But we have a problem, which is that validateOrder has two extra inputs in addition to UnvalidatedOrder. As it stands, there’s no easy way to connect the input of the PlaceOrder workflow to the validateOrder function, because the inputs and outputs don’t match.

priceOrder has two inputs, so it can’t ...