I have found that much of the benefit of functional programming is in the consistent guarantees it makes, not only about your own code but also others' that you

I have found that much of the benefit of functional programming is in the consistent guarantees it makes, not only about your own code but also others' that you depend on. Languages that try to do it all often leave me feeling disjointed. You end up with some libraries written in a strong OOP style, but then others are written with a functional flavor, and then your own code necessarily has to take on a strange amalgamation of the two.