function_composer.go

// given a set of functions defined on our interface
type Functions interface {
	RecordDelivery(x Order) (Order, error)
	ApplyTotals(x Order) (Order, error)
	NotifyMember(x Order) (Order, error)
}

// we can now create a function new function that composes these
// into a new ordering

func ComposeDeliveryFunction(composer FunctionComposer, f Functions) func(x int) int {
  // now we can compose a new function using our building block of functions
  return composer.CreateTransition().
    Map(f.RecordDelivery).
    Map(f.ApplyTotals).
    Map(f.NotifyMember)
}

// now we have a discrete function that can be called to Perform Delivery in a uniform manner	
PerformDelivery := ComposeDeliveryFunction(composer, functionSet)