As an Emacs user, from my experience the Clojure REPL has much better integration with my editor than any non-LISP I've used, which includes Haskell and Erlang. Most of the time I'm not typing commands into the REPL - instead, I'm evaluating code inline, which means I don't need to jump back and forth from the source file to the REPL. It's a much more interactive and productive experience for me, and I haven't been able to fully replicate anywhere else - though it's possible I haven't discovered the right tools for those other languages yet.
When the experience is amplified by homoiconic data structures and structural editing, yes -- exploratory, ephemeral metaprogramming is a breeze. Compound Clojure data literals have a fully readable print representation that can be generically manipulated by built-in core library functions. Say I have a DSL that takes a bunch of nested maps and vectors as an input spec and compiles them to nested closures, and I want to create a large spec derived from some other source satisfying certain constraints, but it's not worth defining yet a higher-level DSL for a one-off definition that I intend to commit to source control. I can generate that data structure any way I like and spit the result out at the REPL or in an interactive buffer, then effortlessly plop that structure or any of its substructures into an EDN file or just inside a `def` or `let` binding in a regular Clojure file, which I then pass to the DSL compiler. It's much simpler than manipulating things like GADTs in Haskell. Even in Common Lisp, it might require some ad-hoc parsing code to accomplish the same thing.
Yes, you can reload any symbol in the CLJ REPL directly from the editor. You can also evaluate any function within the context of the running application without going through the main. The REPL is an integral part of the development process in Clojure. You can see this in action here around 15 minute mark https://www.youtube.com/watch?v=nItR5rwP4mY
R and RStudio are actually quite good in this aspect.
- You can evaluate any part of editor in console with keyboard shortcut. The only difference between using console and editor is that your input is easily saved in editor.
- The environment browser make inspecting variables, data structures much easier.
Besides, in R you want to use vectorized functions for better performance, so you search for general functions and combine them, which actually promote good functional programming style instead of a big control block with many processes intertwined.
I use CIDER with Emacs for Clojure integration: https://github.com/clojure-emacs/cider