Nicolas Frisby
writes:
For the "minor point", you'd like for example the following equivalence (modulo decomposing the Attr type)? ...
Thanks Nicolas No, I do want a list result. it's a different list element I want. So I can go: toAttrs (undefined `asTypeOf` head (toAttrs (FooD 7, ...))) (Compare: typeOf $ typeOf ... The applicable Relational Theory here is that any data structure can be represented as a Set (List) of tuples, each tuple element being a Name with value of some type. And since that applies for _any_ data structure, it must also apply for the structure of structures.) So instead of returning Attr: data Attr = Attr TypeRep TypeRep deriving (Show) Return a tuple of: newtype AttrAttrib = AttrAttrib TypeRep deriving (Show, Typeable, Generic) newtype AttrBasedOn = AttrBasedOn TypeRep deriving (Show, Typeable, Generic) toAttrs :: (Generic product,ToAttrsR (Rep product)) => product -> [(AttrAttrib, AttrBasedOn)] toAttrs = map (\(Attr a b) -> (AttrAttrib a, AttrBasedOn b)) . toAttrsR . from
So:
1) Have I understood your specification correctly?
No, but I've learnt something more about the power of Generics.
2) Other experts: is there safe trickery to generally specify this map? I think it might actually be doable in 7.4, but as far as I know, that was accidental generally-unsound functionality that was removed in 7.6+.