Stratego -- Strategies for Program Transformation
Aster is an attribute grammar system based on Stratego. It makes use of the standard Stratego facilities such as pattern matching and concrete syntax to specify attribute equations and associate them with nodes of an abstract syntax tree. To abstract from these basic equations, users can specify attribute decorators that provide an abstract evaluation mechanism for attributes. Inspired by Stratego's rewriting strategies, these can be used to provide separation of concerns between the basic equations and high-level global search or traversal patterns to be taken on the tree for their evaluation. For example, these can be used to specify automatic copy rules, such as a downward copy rule that copies an attribute value from the parent node if it is not defined at the current node, and recursively higher up in the tree.

Attribute decorators can be used to describe different various high-level attribution patterns, and are not limited to basic copy rule specifications. For example, these include providing support for collection attributes, declaration lookup attributes, and attributes that require fix-point evaluation of circular dependencies (e.g., for data-flow equations). These patterns are often implemented as extensions of the basic attribute grammar paradigm in other systems, "baked into" different attribute evaluator systems. Rather than supporting these in the attribute evaluation system itself, Aster allows to provide these as a library of decorators, and lets users specify their own, often domain-specific decorators by hand.

Project Information

Aster has been developed by Lennart Kats.

Contact and Mailing List

Please send questions to the mailing list or contact Lennart Kats directly. Also, the developers are usually available on IRC at #stratego on (web version). Feel free to drop by!


Aster is LGPL (GNU Lesser General Public License) software. This means that you can use it without being required to distribute your software under the GPL.


Source Repository

The full source code is available from Subversion:

Daily builds

Distributions are built continuously:


Lennart C. L. Kats, Anthony M. Sloane, Eelco Visser. Decorated Attribute Grammars. Attribute Evaluation Meets Strategic Programming. In Proceedings of the 18th International Conference on Compiler Construction (CC 2009), Volume 5501 of Lecture Notes in Computer Science, pages 142157. York, United Kingdom, Springer-Verlag, March 2009. [abstract] [pdf] [bib]


Decorated Attribute Grammars (CC 2009)

Related Software

The Transformers project incorporates a Stratego-based attribute grammar system into SDF for disambiguation of context-free grammars.