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by lmkg 3404 days ago
> "Turing completeness" doesn't mean "I can run a program written in X in Y's runtime."

It's not the definition of Turing Complete, but it is a provable property of Turing-Completeness. If Y is Turing-Complete, then you can use Y to write an interpreter for X. Then the issue is reduced to arguing about what the word "in" means in the phrase "run Python 2 in Python 3."
1 comments
thehardsphere 3404 days ago
Actually it's reduced to the words "in Python 3" because the conflation between the Python 3.x language and the CPython 3.x runtime is something that is prevalent throughout the document.

Just because the maintainers of CPython 3 haven't included a Python 2 interpreter doesn't mean that Python 3 is not Turing complete. Their choice not to do that has nothing to do with the Turing completeness of anything.

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TuringTest 3404 days ago
> Just because the maintainers of CPython 3 haven't included a Python 2 interpreter doesn't mean that Python 3 is not Turing complete. Their choice not to do that has nothing to do with the Turing completeness of anything.

Which is precisely the point that the original version of the essay was making. The joke was on those insisting that it couldn't possibly work, and the punchline was telling them "oh, so what you're saying is that your language is not Turing complete?"

Ok, maybe that doesn't follow the format for a classic joke, but it's certainly a humorous and sarcastic remark.

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joshuamorton 3403 days ago
Except that the original statement isn't really that you can't write a python2 interpreter in python3. In fact, I'm quite sure that those exist somewhere on github, but that there wasn't some kind of transparent interop between py2 and py3.

That is, why can't the cPython3 implementation of the python3 language also execute python2 code? To which I think the simplest response is "why can't the gcc implementation of the C++ language spec link arm-compiled C++ and x86-compiled C++?"

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TuringTest 3400 days ago
> Except that the original statement isn't really that you can't write a python2 interpreter in python3.

That's why Z thinks of this as a joke, not a straight-face assertion.

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joshuamorton 3400 days ago
I don't know what this statement is supposed to mean, could you rephrase or elaborate?
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