Standard design patterns in scala recommend the cake pattern to help compose larger programs from smaller ones. Generally, for simple cake layers, this works okay. Boner's article suggests using it to compose repository and service layers and his focus is on DI-type composition. As you abstract more of your IO layers however, you realize that you the cake pattern as described does not abstract easily and usage becomes challenging. As the dependencies mount, you create mixin traits that express those dependence and perhaps they use self-types to ensure they are mixed in correctly.
Then at the end of the world, you have to mix in many different traits to get all the components. In addition, perhaps you have used existential types and now you must have a val/object somewhere (i.e. a well defined path) in order to import the types within the service so you can write your program. Existential
