A Squeak VM written in RPython
Python C Smalltalk Shell HTML PowerShell Batchfile


RSqueak/VM Linux Build Status Windows Build Status Coverage Status Benchmarks

A Squeak VM written in RPython.


All-in-One bundle for Linux, Windows and OS X:

Download zip Download tar.gz

Pre-built 32-bit binaries:

Download Linux Download Mac OS X Download Windows

Pre-built 64-bit binaries (note that the goal for RSqueak/VM to support all image formats that are <= the native word size - so the 64-bit VMs should open both 32-bit and 64-bit images; it should simply be faster. Due to limitations of the underlying RPython toolchain, Windows binaries cannot currently be built in 64-bit mode):

Download Linux x86_64 Download Mac OS X x86_64

We also have experimental builds for Raspberry Pi:

Download Raspberry Pi 1 Download Raspberry Pi 2 Download Raspberry Pi 3

Finding a working image

Although RSqueak can load images starting with Squeak 2, many primitives are not implemented and instead rely on in-image fallback code to be available and correct. For example, we do not have a BitBlt implementation, so unprepared images will simply stay black. This is why only a Trunk image of Squeak with the latest version of VMMaker from the VMMaker.oscog branch fully works. Try this in a recent Trunk image to prepare it for use with RSqueak/VM:

(Installer squeak project: 'VMMaker') install: 'VMMaker.oscog'.
MCMcmUpdater updateFromServer.

Note that RSqueak/VM will always save images in 32-bit Cog-Spur format, regardless of what it was when you opened it. So make sure to save as new version if you want to keep the original around.

Building from Source

Common to all systems

We have scripts for installing dependencies, building, running the unit tests, and running JIT tests in the .build subdirectory. You need the PyPy source tree, and the rsdl source tree. If you already have all these, run .build/build.py --32bit to build 32-bit VM. Run .build/build.py to compile a 64-bit VM. The script passes all other arguments on to the rpython translator, so you can pass other options.

It will generate a config file .build/buildconfig.ini where you can set your paths. You can also run .build/download_dependencies.py to download the dependencies automatically. You will also need a Python and a C compiler for 32-bit compilation, if you plan to do 32-bit development.


On Windows, you will have to use the C compiler that comes with Visual Studio 2008, because newer ones crash the JIT. It suffices to just install the Microsoft C compiler V90 plus Windows SDK 7. Also, install the Python 2.7 Visual Studio compiler package. The packages provided in the link install it to the default paths. If you already have the compiler and SDK, you can also just update the paths in .build/buildconfig.ini.


RSqueak/VM can currently be compiled in both 32-bit and 64-bit configurations. For 32-bit, you need to use 32-bit python and SDL2 using 32-bit libraries for everything. The easiest way to ensure that is to use a chroot, but you can also install the :i386 versions of the SDL2 dependencies for your distro.

Mac OS X

To compile RSqueak/VM for 32-bit, run


before you run any of the python scripts in the .build directory. You also need to download SDL2 as a framework (homebrew version is not tested). Check the .travis/build-osx.sh if you get stuck anywhere.


The .build directory includes several scripts that make development easier. Once you've setup your system for building, you can use these to work on the RSqueak/VM.


This script executes RSqueak/VM in hosted mode, that is, it runs on top of a Python interpreter. This is very slow (we recommend using PyPy), but it can be useful to debug specific aspects of the VM quickly. Ideally, you set up an image so that it executes the code that you are interested in early during startup (DisplayScreen class>>startUp is a good candidate) and then you add your breakpoints to the source. You can also pass commandline arguments to the script or tweak the default arguments in the script itself.

Running a "Smalltalk REPL"

When you want to work on primitives or plugins, it is useful to prepare an image a little (for example, make it so test runs print to the console), and then run the following:

pypy .build/run.py --shell <PATH_TO_IMAGE>

This will load the image and dump you in a simple REPL for Smalltalk, but with some commands to help you execute Python code and, in particular, to reload the Python code you write in any plugin or primitive file. Thus, you can run some Smalltalk code, check for errors, change the primitive code, reload it, and try again. This avoids having to reload the image in interpreted mode all the time (which can be slow).

There is an integrated help that you can get by typing !help, and there is limited autocomplete, too.

Note that the REPL only loads the image, but does not process startup. For many things, you might want to run FileStream startUp: true or Delay startUp to get basic I/O working or delays working.


The second script that is useful for working on issues regarding the interpreter is unittests.py. By default it runs all tests under the rsqueakvm/test directory (but not those in rsqueakvm/test/jittest/). This is a standalone pytest script, so you can pass arguments or select single test files as you would for pytest.


This script requires that you have already built an rsqueak binary and that you have the C Squeak VM installed. It executes the tests in rsqueakvm/test/jittest/ and checks for the JIT output. We use these tests to ensure that development on the VM does not break JIT optimizations.


This script is useful to figure out what the JIT is doing. Like run.py, it executes the RSqueak/VM in hosted mode, but this time it also simulates the JIT. This is even slower, but allows us to test small code snippets without having to retranslate the entire VM. The code snippets are configured directly in the file. When you run it, it does part of the translation process (but only enough to execute your specific code) and then runs the code. When the JIT kicks in, the compiled loop is shown in a PyGame window. You can then inspect it at your leisure and when you quit the window, the code continues executing. In order for this to work, you need to have pygame and graphviz installed and in your PATH.


This script sets all the environment variables as if for translating the VM, and the drops you into an interactive Python prompt. You can type terminal() to drop into a system shell (%COMSPEC% on Windows $SHELL or /bin/sh on Unices) which then has all the environment variables set up that you need to do manual partial translations or similar things.