[Hs-Generics] Sample code

[Johan Jeuring]

>>         something of the type t1 -> t2 -> t3 where
>>         t3 = f(t1, t2). Generalization of zip/zipWith. I have never
>> seen that example.
>
> how about generic zip?
>
> gzipWith :: (a->b->c) -> C a -> C b -> C c

Good example. In Generic Haskell, gzipWith has type

gzipWith {| t1 :: *, t2 :: *, t3 :: * |}   :: (gzipWith {| t1, t2, t3  
|}) => (t1,t2) -> Maybe t3

gzipWith is a rather standard generalisation (except for the Maybe)  
of gmap, which has type

gmap {| t1 :: *, t2 :: * |} :: (gmap {| t1, t2 |}) => t1 -> t2

so it might not exhibit new properties. But maybe it does lead to  
problems in other approaches.

-- Johan