Mechanically, eMacs is quite close to THI. On THI the LEAP key was the fundamental navigation mechanic. It worked like a SHIFT or CTRL key, but it performed as

Mechanically, eMacs is quite close to THI. On THI the LEAP key was the fundamental navigation mechanic. It worked like a SHIFT or CTRL key, but it performed as an incremental search forward or backwards depending on which LEAP key you pressed. If you pressed (essentially) a META and tapped LEAP, it would search again. Not having used a Canon Cat, I can’t speak to the reality of how well that works. But ^S/^R are pretty close. Of course emacs has all sorts of navigation commands, the Cat had LEAP and PAGE, and part of THI was “one way to do things”. I doubt many rely on incremental search for all navigation in eMacs. The other concept was the modeless operations on selected text. In the Cat the idea was you could type in some simple math, select it, evaluate it, and replace it with the results. Out of the box I’m pretty sure you can select a Lisp expression and replace it with it evaluated result. Either way, you can see how straightforward it is to do whatever you can imagine to a region in eMacs. Pretty sure there’s a way you can adapt eMacs to automatically save and reopen all buffers when you exit and re-enter eMacs. What you lose is the undo history. Anyway, I think that eMacs captures a lot of what THI was trying to do.