Some LISP for Hare?
Posted 2024-06-04. Last updated 2024-11-05.
So, about my new project.
His name is **mice**[^1]. For he is small!
I thought, what am I missing as a programmer? That's right, my own **Scheme** dialect. Of course, the point is not that I just want to write an interpreter. The fact is that the new wonderful programming language **Hare**[^2] lives without the ability to extend application logic with any scripting language. This can't go on any longer! **"How long!"** I thought and sat down to work.
In fact, I expected that much would be unclear to me. But having some experience writing plugins for **Emacs** and a little experience in **Hare** itself, I had an idea where to approach it. I also found an excellent article[^3], which explains in a very basic but clear way what and how to do. I slightly reworked **Hare** lexer, wrote a small **READ**, tweaked **EVAL**. And before I could blink, my interpreter began accepting test code for calculating **Fibonacci** numbers for interpretation!
(define (fib n)
(if (= n 2) 1
(if (= n 1) 1
(+ (fib (- n 1)) (fib (- n 2))))))
After that, I filed **REPL** itself and now it usable!
$ ./mice mice-repl v0.0.0 λ => (define x 12) 12 λ => (+ x 25) 37 λ => (define y (+ x 25)) 37 λ => (exit) Bye!
Of course, there is still a lot of work ahead, but I can handle it. Initially I thought I would add one primitive per week. But implementing **Scheme** on **Hare** turned out to be so easy that in a short time I was able to add almost all the most basic primitives. I think I will have some difficulties with the garbage collector. Something tells me that no one has done this on **Hare** before me. All that remains is to read the documentation and code examples in good old **C**. Fortunately, **Hare** and **C** have comparable capabilities.
As an unexpected bonus, I received another piece of the “understanding technology” puzzle that I was putting together. Now I can say with confidence that I not only understand exactly how machines process commands and perform the operations described in them, but I have also implemented such a machine, albeit at a very basic level and not in hardware. But who knows, maybe someday I’ll get to a stack machine on **FPGA**.
In the meantime, wish me luck, because I have very big plans for this interpreter.
To be continued...
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