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A Squeak/Smalltalk implementation of Babelsberg licensed under MIT

See also Babelsberg/R and Babelsberg/JS

Work in progress.

How to Install

Download prebuilt image

Prebuilt images are published when the tests are green. You probably want the Image, Changes, and Sources. You can also try it online through SqueakJS (but note that this runs very slowly, and does not support Z3).

Install into your own image

  1. Get Squeak 4.5 or later with a recent CogVM for your operating system. Make sure that the SqueakSSL plugin is included (should be true for all official distributions.)
  2. Load Babelsberg/S into your image (You need Metacello¹)
Metacello new
  baseline: 'BabelsbergS';
  repository: 'github://babelsberg/babelsberg-s/repository';

How to develop

If you want to forward development, there are a number of areas that need work. In general, the system needs to be refactored so other constraint solvers (e.g. DeltaBlue) can be added more easily. There are also a number of things that this implementation does not do, yet, that are desirable, such as identity constraints, constraint priorities at time of definition, proper readonly variables, or automatic recalculation of constraints when a complex object involved in the constraint changes identity (the latter is an optimization found in the Babelsberg/R and Babelsberg/JS implementations). Further down the road, the constraints from different constraint solvers should be able to interact (as implemented in Babelsberg/JS).

The repository includes a package, Babelsberg-Tests, that includes the conformance tests generated from the executable semantics. These may be a little outdated if they have not been regenerated in some time, but in any case, a goal for further development should be to improve pass rates on these tests. As a guideline, Babelsberg/JS currently passes 39 of these tests using a combination of Z3 and DeltaBlue (the latter for identity constraints). Getting the number for Babelsberg/S up to mid-30 would be worthwhile.


All files except those in Cassowary.package are under the MIT License.
The files in Cassowary.package are under the LGPL License


In case you do not have Metacello in your Squeak image, bootstrap it like this:

Installer gemsource
    project: 'metacello';
    install: 'ConfigurationOfMetacello'.

"Bootstrap Metacello Preview"
((Smalltalk at: #ConfigurationOfMetacello) project version: #'previewBootstrap') load.

"Load the Preview version of Metacello from GitHub and then load Latest Baseline"
(Smalltalk at: #Metacello) new
  configuration: 'MetacelloPreview';
  version: #stable;
  repository: 'github://Metacello/metacello:configuration';
(Smalltalk at: #Metacello) new
  baseline: 'Metacello';
  repository: 'github://Metacello/metacello:master/repository';
(Smalltalk at: #Metacello) new
  baseline: 'Metacello';
  repository: 'github://Metacello/metacello:master/repository';


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