[Hs-Generics] Request for code review: Generics for tuple/newtype introspection

[AntC]

> Nicolas Frisby <nicolas.frisby <at> gmail.com> 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+.
>