Well, now this is quite the experience.
I’ve been trying Viper for the past few days. Viper, for those that don’t know, is usually described as a set of Vi bindings for Emacs.
After reading the nearly 100 pages of documentation and trying it a bit, I have realized that this is not really an accurate description. Viper is a port of vi to Elisp.
But that doesn’t really do it justice. Viper seems to have pretty much everything going for it that Vim does, and then some. It is extensible with Elisp, and works with all the Emacs major modes (indentation and so forth). Yet it also is a very authentic Vi implementation, yet more customizable than Vim. And, in my opinion, more capable than Vim too.
On the one hand, this is a really neat combination: the power of the vi editing commands with the power of Emacs and Elisp for indentation, customization, etc.
On the other hand, it makes my head hurt. While Viper and Vim both are supersets of the vi command set, they don’t always implement extensions (such as multiple windows) the same way or with the same keys. Of course, you could remap them in both, but it’s a bit jarring to run Viper in expert mode, press C-w to start creating a new window, and have it run the Emacs cut command. (You can run Viper in a more limited mode where it does not recognize any regular Emacs keys if you don’t want that)
It’s just weird. It mostly looks like Emacs. It is modal like Vim, and responds to all Vi and most Vim commands. It has an additional mode: the Emacs mode. Also if configured to run in expert configuration, Emacs commands are accepted most places. Yes, you can move with h, j, k, l and C-n, C-p, C-f, C-b all at the same time.
The main drawback I can see is that Viper mode doesn’t work well with Info mode, which has other bindings for keyboard shortcuts… so all of a sudden, hjkl don’t work in info mode.
I don’t know yet if I’ll use viper much, but it is a slick program.