[Haskell-cafe] Re: SYB with Existentials

[Oscar Finnsson]

OK. That was probably the most complete answer ever.

Under what license are you releasing DataEx.hs? I'm wondering if I may
use it in my package (under BSD3 license) until something like it is
included in SYB.

Pedro: How are extensions to SYB handled? code.google only seems to
handle issues - not tickets.

-- Oscar


On Wed, May 26, 2010 at 8:31 AM,  <oleg at okmij.org> wrote:
>
> The only, non-fatal, problem is _not_ with writing the instance of
> gunfold. Defining gunfold is easy. The problem is that the existing
> SYB -- or, the module Data/Data.hs to be precise -- has
> non-extensible constructor and datatype descriptions (Constr and
> DataType). The problem is not fatal and can be worked around in
> various inelegant ways. Alternatively, one can fix the problem once
> and for all by making DataType and Constr extensible -- along the
> lines of the new Exceptions. The following file
>
>        http://okmij.org/ftp/Haskell/DataEx.hs
>
> demonstrates one such fix. The file DataEx.hs also tries to avoid the
> overlap with Data.Typeable. (One doesn't need to carry the name of the
> datatype's type constructor in DataType. That name can be obtained
> from the result of typeOf). The file DataEx can be used alongside the
> original Data.hs. The code below uses DataEx in that way, to
> complement Data.hs. The hope is that the maintainers of SYB might
> choose to extend Data.hs -- perhaps using some bits or ideas from
> DataEx.hs.