> Hmm, not sure I understand. How are those shell based?

A shell is just a programming language that's well suited for interactive repl use. Compare https://en.wikipedia.org/wiki/Scsh

Of course, Rust and Haskell aren't typically thought of as shells. Though if you wanted to and felt brave enough, you could use ghci as a shell.

> I guess my poorly worded claim was less focused on the OO nature of psh than on the typization (which both of these also do) - if you knew what type $rev and $path are, it's easier to distinguish intent, whether objects or not.

Agreed!