I use a separate tool to call a lot of functions written in C. That tool is called “Python”. Or “Ruby”.
Sometimes I use a separate tool to call functions written in Python (or JavaScript, or...) and that tool is called PostgreSQL.
Sometimes I use Ruby to call C to call Postgres to call JS.
> Now that we have better languages, why not use them to write the OS bottom-up?
What better languages for implementing an OS? Lisp? We had that before C. Rust? Either way—and I like both languages—I don't want to use either for a shell. Red? Maybe, but I don't think we're to the point of a Red OS yet, and while it's probably eventually usable for that purpose, I don't see it as necessarily ideal for OS implementation though it might be tolerable as a shell language.
There is a long history of alternative shells csh, tcsh, zsh, fish, etc. All with various level of abstraction and various amounts of "programming language type constructs" (for lack of a better term).
At the end of the day, long arguments have been had over which is the better shell. It's all just personal preference. Hence it can be set in /etc/passwd per user.
You prefer python? chsh is there to change it.
Space on a line is limited and one directional, so thr tools naturally evolved towards strange single line incantations instead of full fledged programs.
Commodore Pet did it right by introducing a navigable terminal where you could move between lines and don't need to open an editor to write multiline programs.
Modern CLIs can usually emulate at least a few of the old scrolling character matrix displays, but only a few bash commands (e.g. top) use the extra features.
But mm... why you would want to mutable state like current directory in first place? Or even mutable filesystem? Why aren't those just immutable parameters of your program?
Because that's how just about any OS, application, library, filesystem, device driver, database, nearly everything related to computing at all, works. Reinventing the universe has never, ever lead to success. If you want even the slightest hope for non-negligible adoption of your operating system, you need to be able to interface with the rest of the world. And that's why you don't want the filesystem to be an "immuatble parameter of your program".
> any OS, application, library, filesystem, device driver, database, nearly everything related to computing at all
-is trying to actually do to your files and operation like reverting changes is trivial. Sure it's not performance optimal and effects what kind of software is ideal to work within such a system. It's just a different approach with different trade-offs.
Anyway if I one day want to build new OS it's for trying different interesting approaches and not yet another 'successful any-OS'.
You can actually consider current directory as immutable already.
It became "badly mutable" for example if you manipulate the current directory and this change is observable from a program point of view which is already running. Would that be really useful?
To clarify I am not trying to say that absolutely everything should be immutable but it's fun thought experiment how far you can go.
Being immutable doesn't mean that everything is static but that things aren't changeable in place. So instead of having a global mutable state, you have this local state which you can alter by creating new instances and passing them around. In the end, the difference is that on what scope changes are observable and how that constraint effects on your design. In some sense: mutable = changes are uncontrollable, immutable = changes are controllable.
I’m not saying POSIX shells are without fault but they weren’t just created because C is too low level; they were created because people used a terminal who weren’t always techies so Bell Labs created a language which anyone could easily write simple programs with. Granted that need has dissipated a little but your solution of having one language to rule them all creates more problems than it solves (really the only problem it solves is OCD for a few LISP enthusiasts).
The reason there are so many different programming languages isn’t just an element of NIH; some languages do genuinely handle some use cases better than some other languages. Plus there is always going to be an element of user preference. So your idea of a perfect system would be hell for a great many other people - myself included (and I do generally enjoy functional programming).
At some point when I wasn't proficient enough in Bash yet, I was writing scripts for automation using Perl and Ruby. The 'logic part' is definitely much easier in these languages. But simple file/directory stuff is far more complex actually. A lot of this has to do with error handling and different expectations how that is supposed to work. In a default shell script, errors are handled very forgivingly which is very much how most people work when performing tasks manually - not every step is super important.
On the other hand Shell scripting documentation is crap. Most of it is from 80s/90s, full of irrelevant details for the practical person. A bit like 90s/00s JS documentation before MDN.
Compare Rust, which tries to keep allocations (and the size/asymptotic complexity of allocations) explicit and visible.
[1] The optimizer catches some cases, but not all of them.