[Haskell-cafe] Conditional code for Haddock

[Daniel Fischer]

Am Mittwoch 20 Januar 2010 12:20:55 schrieb Roel van Dijk:
> I want to generate documentation for the following code snippet:
> > import qualified Data.ByteString as BS ( ByteString, length )
> >
> > -- | Foo 'BS.empty' equals 0
> > foo ∷ BS.ByteString → Int
> > foo = BS.length
>
> Because I do not explicitly import BS.empty haddock will not generate
> a nice link.
>
> I can fix it by adding:
> > import qualified Data.ByteString as BS ( empty )
>
> But now the compiler rightly warns me:
> > Warning: Imported from `Data.ByteString' but not used: `BS.empty'
>
> There is a ticket related to this problem [1], but I do not think making
> haddock 'magically' find BS.empty is the right answer. What I would like
> to
>
> do is:
> > #ifdef __DOC__
> > import qualified Data.ByteString as BS ( empty )
> > #endif
>
> Because I use additional symbols in my comments it feels natural to also
> have special imports for them.
>
> I know that cabal used to define the __HADDOCK__ macro. Is it possible
> to manually define a preprocessor macro when haddock is run? Perhaps an
> equivalent to ghc-options: haddock-options?

Doesn't haddock define __HADDOCK__ by itself?

I would've thought

import qualified Data.ByteString as Bs
    ( ByteString
    , length
#ifdef __HADDOCK__
    , empty
#endif
    )

should work.

>
> Ideally I want only have to add the following to my .cabal file:
> > haddock-options: -D__DOC__
>
> Regards,
> Roel van Dijk
>
>
> 1 - http://trac.haskell.org/haddock/ticket/78