Turns out I made some unnecessary “work” for myself when I tried to add support for command history to inf-mongo. As Mickey over at Mastering Emacs points out in a blog post, comint mode already comes with M-n and M-p mapped to comint-next-input and comint-previous-input. And of course they work in inf-mongo right out of the box. I still prefer using M-up and M-down, plus I learned a bit about sparse key maps and general interaction with comint-mode. So from that perspective, no time was wasted although it wasn’t strictly necessary to put in the work.

I’m spending a lot of time in the MongoDB shell at the moment, so of course I went to see if someone had built an Emacs mode to support the MongoDB shell. Google very quickly pointed me at endofunky’s inf-mongo mode, which implements a basic shell interaction mode with MongoDB using comint. We have a winner, well, almost. The mode does exactly what it says on the tin, but I wanted a little more, namely being able to scroll through my command history. Other repl modes like Cider have this functionality already, so it couldn’t be too hard to implement, could it?