Seen this feature in Jason Gilman talk about proto-repl Atom package. It allows you to explore nested maps, vectors, lists in pop-up window, which I think is quite useful. Emacs has child-frames, hideshow-mode, and clickable fringe, which I think are the ingredients for this feature.

I will not go for really complex example, so here's a simple map, and we assoc-in new value to a nested map in it. Here's what cider displays:

This indeed usable, but proto-repl takes this concept further:

And I think it makes perfect sense to truncate such output if we provide feature to explore it:

There are many different packages that provide interactive stuff through child frames, like lsp-ui:

This popup can be scrolled with mouse, focused and resized. Or company-posframe:

These are two child frames side by side, we can interact with both by using specific keybindings.

---

Sorry if I missed feature request for this feature, I've searched with proto and proto-repl queries and found only 1 closed issues that is related to proto-repl:

• Show which form has been evaluated #1689