Re: C bindings

[Shahbaz Youssefi <shabbyx-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>]

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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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