unified and extensible annotations

We have several annotations in current Haskell: deriving, pragmas {-# #-}, ! ! (DrIFT), haddock... These are ad-hoc, and not extensible by the programmer.

There are better ways:

• C-sharp has "custom attributes".
• Java (1.5) has "annotations".

For me the important features are

• An annotation is allowed basically at any declaration,
• and programmers can define their own annotations,
• and annotations can also have values.
• Also, they have a retention policy saying whether they should be visible at compile time or at run time, where compile time is for tools/preprocessors, and visibility at run time is helpful for reflection. (Would need some support from Data.Generics or thereabouts.)

I have brought this proposal up on the mailing list and there was one response.