[jswiente]

It depends on the level of abstraction and the view of the system that should be described. A model of the structure of a system with components, subcomponents and their relationship with each other does not include any information about the actual implementation of the components and the programming paradigm being used. Also, a data model of the business domain is not concerned with any technical detail such as the components or subcomponents the system. You can model all these artifacts using UML.

Of course, using an UML class diagram for a detailed design describing the implementation of a component does not make sense when using functional programming.