Hello Simon,
I'm not sure what you intend here. Can you be more concrete?
A concrete example could look like this, {-# ANN T $(defaultValue [| T { foo = 1 } |]) #-} data T = T { foo :: Int, baz :: Int } where defaultValue :: Q Exp -> Q Exp would encode the value in a suitable form. The intention is to specify default values for some fields of the record. Then, later, I want to generate a parser for T, that takes the default value into consideration, in order to make the foo field optional and the baz field mandatory. $(deriveParser ''T) Inside deriveParser, I want to access the annotation of T. That requires a function like getAnnotations :: (Typeable a, Binary a) => Name -> Q [a] which does not exist. So the first question is, Would adding this function be feasible? If yes, what sort of stage restrictions would be required to make it work? Continuing the example above, I can achieve the same effect by passing the default value in some form as an argument to deriveParser. But I'd prefer using an annotation because then I only have to specify that value once even if there are several chunks of generated code that rely on a default value. A second advantage is that an unused annotation does not add any clutter to the code at all -- it can be completely optional. So in my eyes this feature would be ideal for specifying exceptional handling of a few data types (or functions or constructors) from Template Haskell code. Of course there are disadvantages as well, foremost that it'd be yet another ghc specific extension. So the second question is, is the idea really useful enough to justify being implemented? regards, Bertram [annotations] http://hackage.haskell.org/trac/ghc/wiki/Annotations