I’m looking for a way to decorate a servant API definition: Whenever an endpoint returns a list of things, I’d like to add a query parameter.
So far, I have a type family that works on APIs that are defined with the traditional approach using :<|>:

We are writing custom Servant combinators to handle “resource authorisation” in our application. So we don’t have to explain the domain itself, I’m going to use a task list app as an analogy.