I am now studying new approaches to harmony in the Romantic and Impressionistic eras, but I haven't seen anything about formal functions.
It seems like even if they were still using Sonata form (which based on my basic study of Debussy, doesn't seem the case at least by the early 20th century), the definition of a sonata would have to be fundamentally changed to fit the sort of harmonic innovations that were happening.
What are some approaches to analyzing particularly form of the late Romantic/Impressionistic eras? (I don't know if I'm allowed to say this, but recommendations for relevant resources would be appreciated as well as answers).