I agree with your point that IDEs are getting better but REPLs are getting better too, why should they be relegated to be mere artifacts of the past. Your java REPL will mostly have autocomplete, give it a chance, it really might turnout to be fun :P
And typing python in a REPL is fun for me, but fun is subjective, no point arguing about it :)
I use REPLs all the time... Bash is basically a REPL :)
The reason I think Java REPL would be awful is not because I dislike REPLs but because Java is really painful for that kind of mutable command line like development. Like just making a damn struct like object is absolutely painful and Java does not have structural types (ignoring FunctionalInterfaces which isn't really structure types).
Python REPL is painful because of required indentation and again because Python is similar to Java and prefers nominal types.
I'm not against Python or Java but I don't think the language design of those languages really works well for REPL compared to say Lisp, OCaml, Haskell, or even Scala and Smalltalk.
Secondly the image we two have in mind of a REPL seems to be different. When I am thinking about a REPL the image I have in mind is of Jupyter Notebook and Clojure, Elixir, Idris, Haskell REPLs in Emacs. The image you have in mind seems to be a basic console, so having spent my day working in a Jupyter Notebook I sit here thinking what you mean by Python's significant whitespace being an issue(Haskell and Idris have significant whitespace too). But now I do understand your views :)
P.S. I didn't get your point about python having nominal types, duck typing seems closer to structural typing to me and mypy seems to support both, but maybe I misunderstood you. Thanks for the thought provoking discussion though :)
Thats my point is that the REPL case of using Emacs to run and evaluate your code is almost hardly different than letting an IDE run your unit test. With Java this evident because the IDE compiles incrementally and the debugger can hot code swap.
The power of the REPL should not be the evaluation portion but the input or the print otherwise you can just about do any quick evaluation for any language that compiles reasonable fast.
Other than Jupyter Notebook the ones you mention don't really have any amazing output other than pretty print. To the authors point it also helps for the pretty print if the language is homoiconic.
As for input there is even fewer that have Excel like rapid response feedback. See Bret Victor on this. There was a recent company presented here on HN called Luna [1] who have a very cool REPL. Now that is where I think REPLs should be.
> P.S. I didn't get your point about python having nominal types, duck typing seems closer to structural typing to me and mypy seems to support both, but maybe I misunderstood you. Thanks for the thought provoking discussion though :)
For the most part you need to name functions in Python (lambda support I believe is even on the way out but I can't recall the status). In fact other than I guess tuples you need to name everything in Python.
But to your point structural typing means less in a duck typing environment particularly one with really late dispatch.
Using a REPL vs. an IDE like you describe is the difference between a conversation and sending somebody a letter with instructions.
This is more visible when we use more dynamic languages/runtimes than Java/JVM. Since the changes one can do and how they need to be done is not very advanced, the usefulness of a REPL is reduced.
