Would it just be easier if we derived Data and Typeable instances in pandoc?

On Tue, Feb 24, 2015 at 2:39 PM, Shahbaz Youssefi <shabbyx-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> wrote:

> Hi,
>
> I'm updating libpandoc to align with pandoc 1.13, but I'm currently having
> a compilation issue that is beyond my understanding.
>
> In [LibPandoc/Instances.hs](
> https://github.com/ShabbyX/libpandoc/blob/master/src/LibPandoc/Instances.hs),
> there is the following code, that had been working with pandoc 1.11:
>
>     {-# LANGUAGE TemplateHaskell #-}
>
>     module LibPandoc.Instances where
>
>     import Data.Data
>     import Data.DeriveTH
>     import Text.Pandoc
>     import Text.Pandoc.Shared
>     import Text.Highlighting.Kate.Types
>
>     $( derive makeTypeable ''ReaderOptions )
>     $( derive makeData ''ReaderOptions )
>     $( derive makeTypeable ''WriterOptions )
>     $( derive makeData ''WriterOptions )
>     ...
>
> From what I understand, `derive makeData` does some magic, so that later
> one could say `deriving (Data)` for a type that contains `ReaderOptions`
> and `WriterOptions`.  With newer pandoc, it seems that some types were
> added.  With `TrackChanges` used in `ReaderOptions`, I can add similar
> `derive makeTypeable/makeData` lines and everything is ok.  With `MediaBag`
> used in `WriterOptions` however, I can't do this.
>
> Without `derive makeData` for `MediaBag`, I get the following error for
> `$( derive makeData WriterOptions )`:
>
>     No instance for (Data MediaBag) arising from a use of `k'
>     Possible fix: add an instance declaration for (Data MediaBag)
>     In the expression:
>         ... A VERY LONG EXPRESSION WITH A LOT OF `k` INFIX CALLS ...
>
> If I add `$( derive makeData MediaBag)` before, I get this error on it:
>
>     Not in scope: data constructor `MediaBag'
>
> I have `import Text.Pandoc.MediaBag`.
>
> From what I could make out, the reason is probably that others, such as
> `TrackChanges` are defined with the `data` keyword, but `MediaBag` is
> defined with the `newtype` keyword.  Is that so? How then, can I make `$(
> derive makeData ''MediaBag)` work? If not possible, how can I make `$(
> derive makeData ''WriterOptions )` work?
>
> Thanks for the help,
> Shahbaz
>
> On Sunday, June 30, 2013 at 8:30:37 PM UTC+2, fiddlosopher wrote:
>>
>> Thanks for doing this.  I've updated pandoc-extras.
>>
>> +++ Shahbaz Youssefi [Jun 30 13 13:04 ]:
>> >    Hi again,
>> >    I updated libpandoc (for C bindings) to the current version of
>> pandoc
>> >    and made some improvements. I sent a pull request to toyvo, but it
>> has
>> >    been left unanswered (he's probably not so active on github). In the
>> >    meantime, you could
>> >    [refer]([1]https://github.com/jgm/pandoc/wiki/Pandoc-Extras) to my
>> fork
>> >    at:
>> >    [2]https://github.com/ShabbyX/libpandoc
>> >    Have a nice day,
>> >    Shahbaz
>> >
>>
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