PyPy.js: PyPy compiled into JavaScript

PyPy. Compiled into JavaScript. JIT-compiling to JavaScript at runtime. Because why not.

This is a very-much-in-flux collection of supporting scripts and infrastructure for an experimental emscripten/asmjs backend for PyPy, as described here:

https://www.rfk.id.au/blog/entry/pypy-js-first-steps/

For the history of the project, see NEWS.

The actual PyPy backend is maintained as a git submodule pointing to a fork of a github clone of the upstream PyPy repository:

https://github.com/rfk/pypy

You can get all the necessary code from within this top-level repository by accessing it as a git submodule:

$> git submodule update --init

Building pypyjs requires a 32-bit python environment and the emscripten-enabled LLVM toolchain. The recommended way to build is using the pre-built docker image containing these dependencies:

$> docker pull rfkelly/pypyjs-build

The Makefile knows how to use this image transparently during build and test. You can run various parts of the testsuite like this:

$> make test-js-module
$> make test-jit-backend

Do do a full build of the PyPy VM like this:

$> make

Be prepared, this will take a long time. It will eventually produce the file ./build/pypy.vm.js containing the code for the interpreter. This goes together with support files in ./lib/ to make a complete distribution.

To get a full release tarball, do:

$> make release

Take a look in the ./website/js/ directory for an example of how to distribute and use the resulting bundle.

To build from an in-progress branch of the pypy repository, check it out in the submodule like so:

$> cd ./deps/pypy
$> git checkout whatever-branch
$> cd ../../
$> make

If you'd like to hack on PyPyJS, the following background reading will be helpful:

• https://rpython.readthedocs.org/en/latest/translation.html
• https://pypy.readthedocs.org/en/latest/coding-guide.html

We have the following major components in the PyPy repo:

• An "emscripten" build platform definition, which teaches pypy's rpython toolchain how to compile things with emscripten: ./deps/pypy/rpython/translator/platform/emscripten_platform/.
• An rpython JIT backend that emits asmjs at runtime: ./deps/pypy/rpython/jit/backend/asmjs/.
• A "js" builtin module for the resulting interperter, to allow interaction with the host javascript environment: ./deps/pypy/pypy/module/js/.

Along with these wrappers to help working with the resulting interpreter:

• A wrapper to load up the compiled VM and expose it via a nice javascript API: ./lib/pypy.js.
• A script for bundling python modules into an indexed format that can be easily loaded into the browser: ./tools/module_bundler.py.