what's the point of rpython?

Brendan Miller catphive at catphive.net
Sat Jan 17 01:37:39 CET 2009


So I kind of wanted to ask this question on the pypy mailing list..
but there's only a pypy-dev list, and I don't want to put noise on the
dev list.

What's the point of RPython? By this, I don't mean "What is RPython"?
I get that. I mean, why?

The goals of the pypy project seems to be to create a fast python
implementation. I may be wrong about this, as the goals seem a little
amorphous if you look at their home page.

So, to do that this RPython compiler was created? Except that it
doesn't compile python, it compiles a static subset of python that has
type inference like ML.

This RPython thing seems like a totally unnecessary intermediate step.
Instead of writing an implementation of one language, there's an
implementation of two languages.

Actually, it seems like it harms the ultimate goal. For the
interpreted pyton to be fast, the interpreter has to be written in a
reasonably fast language. ML, and C++ compilers have had a lot of work
put into their optimization steps. A lot of the performance boost you
get from a static language is that knowing the types at compile time
lets you inline code like crazy, unroll loops, and even execute code
at compile time.

RPython is a statically typed language because I guess the developers
associate static languages with speed? Except that they use it to
generate C code, which throws away the type information they need to
get the speed increase. Huh? I thought the goal was to write a fast
dynamic language, not a slow static one?

Is this going anywhere or is this just architecture astronautics?

The RPython project seems kind of interseting to me and I'd like to
see more python implementations, but looking at the project I can't
help but think that they haven't really explained *why* they are doing
the things they are doing.

Anyway, I can tell this is the sort of question that some people will
interpret as rude. Asking hard questions is never polite, but it is
always necessary :)

Thanks,
Brendan



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