[Hs-Generics] compositional gMap in SYB1

[Johan Jeuring]

> I have done so. I have committed a new version of
> 	/comparison/SYB1_2/GMap.lhs
> with gmap2 of the type

Interesting.

>> gmap2 :: forall a b c . (Data a, Data b,
>> 		           Data (c a), Data (c b), Data (c X)) =>
>>         (a -> b) -> c a -> c b
>
> The compositionality tests seem to pass. There are no unsafe
> operations or any unsafe extensions. Only standard Data.Typeable and
> Generics.Data operations are being used. The code also contains an
> optimization: if it is determined that a structured value has no
> components to map, no traversal is performed and the value is returned
> as it is. That should speed things up a little. The trick is producing
> something out of nothing.
>
> 	Too bad that the deadline to amend a Haskell workshop paper
> has passed, and so has the deadline for the generics workshop. Perhaps
> we should write a separate paper?

We're thinking about extending the Haskel Symposium paper to a journal
version, in which we would also take efficiency into account (i.e., also
try to set up something like a benchmark for generic programming).
Would something like that be suitable you think?

-- Johan