The interactive development workflow in Idris is best described as type driven development and the focus seems to be on making the REPL an interface where an intelligent dialog can happen in between the programmer and the compiler, with the compiler trying to nudge you in the right direction. It is kinda fun, you should definitely check it out[1].

And regarding your point about the modern IDE workflow, I personally think that the sweet spot is somewhere in between, I personally prefer having a REPL process in the background I can interact with while still writing code in my source file and a REPL kept open as a scratch space where I can experiment freely without messing up my source code, I feel much better experimenting in a REPL, but to each his own I suppose :)

Jupyter Notebook is a completely different beast though, modern REPL + literate programming, what's not to love.

[1] -- (https://www.manning.com/books/type-driven-development-with-i...)