[deno2]

REPL Driven development as it's called is really yes having your whole system running at your thingertips (even production for the adventurous). You can execute arbitrary code and get results or see what state has changed. You can also redefine anything (in Clojure at least) that is referred to, such as functions and variables (I use these terms loosely here).

Normally you have your IDE configured so that anything executed is executed in the context of the running REPL session. So there should be no need to copy/paste.

When done properly with tests running on every change you really can't, as a developer, get any quicker feedback. It's brilliant and empowering!

Your issue could be emacs but, for Clojure at least, there is the Cursive Intellij plugin which is now definitely usable. Also there are the brand new IDEs like LightTable.

LightTable.com started out with some very different ideas with regards to code organisation and there is still a lot of potential work there. But lighttable instead became open source and a core for plugins. The plugins now range from rainbow parentheses to 'pick your language' evaluation.

If you want to discuss any of these ideas or others please do or PM me. I'm always willing to discuss as my girlfriend is hopeless. But then for everything not programming she keeps me sane.