Note that syz is essentially based on Data.Data, which is no less "official" than GHC.Generics. (The compiler can derive Data with -XDeriveDataTypeable.) I am not sure what your primary concern is. In case you are concerned with the ease of deriving generic instances, almost every generics library out there, including traverse-with-class, provides a TH function for deriving the necessary instances. You can write a zipper based on GHC.Generics, but it won't be a straightforward translation of syz (nor would it be a trivial undertaking). Roman * Luke Evans [2013-04-10 16:38:17-0700]

Hmm, in my naivety I failed to notice that the 'official' GHC.Generics are completely different to SYB on which syz is built. Classic case of reading the same words/names and assuming they're exactly the same thing.

Maybe it's not that hard to rewrite syz in terms of GHC.Generics.Generic (I'll perhaps take a look), but maybe there's a generic Zipper library already based on the GHC stuff?

On 2013-04-10, at 3:19 PM, Roman Cheplyaka wrote:

...

...Apart from that, I am not aware of any problems with syz.

Roman

Hi Luke, Even though you might have made up your mind already, here's some more info. If you want a zipper that does not use Typeable (and thus runtime type comparison and casting, which are potentially inefficient), you can use the zipper in Multirec [1]. Creating a zipper based on GHC.Generics should be easy taking the zipper based on instant-generics [2], or you can just use Sean Leather's rendering [3]. Cheers, Pedro [1] http://hackage.haskell.org/package/multirec [2] http://hackage.haskell.org/package/instant-zipper [3] https://github.com/spl/generic-deriving-extras On Thu, Apr 11, 2013 at 8:44 AM, Luke Evans wrote:

Thanks Roman.

I'll probably go with Data.Data then. Certainly, I'm not looking for any significant distractions and I'll heed your cautionary note. I read that GHC.Generics is fit and fast in comparison to SYB, but that's not really a big concern for me at the moment. I just fell in to believing that GHC.Generics was the true religion given its apparent status as the adopted generics in GHC.

On 2013-04-10, at 11:24 PM, Roman Cheplyaka wrote:

...

Note that syz is essentially based on Data.Data, which is no less "official" than GHC.Generics. (The compiler can derive Data with -XDeriveDataTypeable.)

You can write a zipper based on GHC.Generics, but it won't be a straightforward translation of syz (nor would it be a trivial undertaking).

Roman

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