Macro annotations

Eugene Burmako
15.11.2011

I'm excited to announce that we've decided to introduce a third flavor of macros into project Kepler, namely: macro annotations. These macros are very much inspired by Nemerle, but there are some important differences.

In line with the idea of transparent embedding into the language, macro annotations look the same as regular annotations, but instead of being static participants of the compilation, they trigger AST rewriting. As of such, macro annotations are expanded strictly after all other macros applicable to the annottee (e.g. macro annotations for a class kick in after all macro types get expanded and after the entire inheritance chain is resolved and the members are mixed in).

We have also played with the idea of macro annotations affecting outer scopes as well. For example, if we put a @lazy macro annotation on a parameter of some method def m(@lazy x: T), then we'd really like the annotation to overwrite the entire method. However, it's not perfectly clear how far upwards we should go (e.g. it might also be reasonable to wish that a member annotation rewrites the entire class), so we decided to do away with this idea for the moment.

Later today or tomorrow I will update the site with examples and further details about macro annotations. Stay tuned and let us know what you think at dev@scalamacros.org.