Could either of those approaches (FRP / Delimited Continuations) be a solution for implementing complex GUI code?

I think the answer is generally yes; I have tried writing a user interface which has a form with several controls; a change in one control may affect all other controls on the form (or change the form). I have tried it for a particular GUI: the web page -- displayed in a browser interacting with a CGI script. The choice of CGI was deliberate because it is harder than FastCGI: it requires the ability to save the state of the interaction. The continuation must outlive its process. The point I was trying to make is that the GUI is programmed as if it were a uncursed console application: you send one question, get a reply, send another question, etc. With a GUI, questions are sent in parallel and answers are delivered in any order; yet the programmer can still think he deals with a regular console application; as if the interaction never happens and the program merely reads the data from a file. http://okmij.org/ftp/Computation/Continuations.html#shift-cgi It was done in OCaml though (because OCaml has native persistent delimited continuations).