> Byterun is a Python interpreter written in Python. This may strike you as odd, but it's no more odd than writing a C compiler in C.
I'm not so sure. The difference between a self-hosted compiler and a circular interpreter is that the compiler has a binary artifact that you can store.
With an interpreter, you still need some binary to run your interpreter, which will probably be CPython, making the new interpreter redundant. And if you add a language feature to the custom interpreter, and you want to use that feature in the interpreter itself, you need to run the whole chain at runtime: CPython -> Old Interpreter That Understand New Feature -> New Interpreter That Uses New Feature -> Target Program. And the chain only gets longer, each iteration exponentially slower.
Meanwhile with a self-hosted compiler, each iteration is "cached" in the form a compiled binary. The chain is only in the history of the binary, not part of the runtime.
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Edit since this is now a top comment: I'm not complaining about the project! Interpreters are cool, and this is genuinely useful for learning and experimentation. It's also nice to demystify our tools.
PyPy handled this by implementing PyPy in a restricted minimal subset of Python that they called RPython, and that seemed to work out well for them.
Oooh it's a bytecode interpreter! I was wondering how they'd fit a parser/tokenizer in 500 lines unless the first was `import tokenizer, parser`. And it looks like 1500ish lines according to tokei
I think because python is a stack-based interpreter this is a really great way to get some exposure to how it works if you're not too familiar with C. A nice project!
Very well written! Everyone used to tell me during Uni that stacks are used for running programs, never ACTUALLY understood where or how.
the article glosses over something worth pausing on: the `getattr` trick for dispatching instructions (replacing the big if-elif chain) is actaully a really elegant pattern that shows up in a lot of real interpreters and command dispatchers, not just toy ones -- worth studying that bit specifically if you're building anything with extensible command sets.
And, in some ways, PyPy. I still think it is the sanest way to implement Python.
It makes me sad that I have to write C to make any meaningful changes to Python. Same goes for ruby. Rubinius was such a nice project.
Hacking on schemes and lisps made me realize how much more fun it is when the language is implemented in the language itself. It also makes sure you have the right abstractions for solving a bunch of real problems.
> And, in some ways, PyPy
What do you mean by that? I'm not familiar with PyPy
PyPy is python implemented in python. It is fast.
It lags behind CPython in features and currently only supports Python versions up to 3.11. There was a big discussion a month ago: https://news.ycombinator.com/item?id=47293415
But you can help! https://pypy.org/howtohelp.html
PyPy is python implemented in RPython, which is technically a python subset. It's so restricted it might as well be a different language though.
It is restricted in a way that you would restrict yourself to write high speed software in most languages, and I found it is not that restrictive compared to C that you would have to use if you were to write a fast Python library.
oh for sure, but I still feel like telling people pypy is written in python is misleading. it's written in something significantly like python, but it's not python.
> technically a python subset
So it can just run under CPython? If so, then that isn't too misleading.
Yes. It can run under Cpython (2.7).
Well, one could rewrite Python (perhaps piece by piece?) in Shedskin.
Shedskin is very nearly Python compatible, one could say it is an implementation of Python.
aka A Metacircular Interpreter
"Yaw dog I heard you liked python, so I put python in your python so you can interpret python while you interpret python"
Just wondering why you stopped there? Why not a python interpreter for a python interpreter for python ?
It already is that.