function_composition.go

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

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

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

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