1) we could modify `@rule`s to remove all complex selectors from the

@rule(...)

signature, meaning that what happens statically is only the simplest type of conversions:

Select

, and nothing else. then, we would imperatively implement things like `SelectDependencies`/`SelectProjection` in the

@rule

body using the generator syntax we've discussed (ie

classpaths = yield [Select(Classpath, d) for d in target.dependencies]

)