[Haskell-cafe] Re: AlternativePrelude extension

[Roel van Dijk]

On Sun, Jan 17, 2010 at 12:27 PM, Ketil Malde <ketil at malde.org> wrote:
> I think there might be justification for doing it multiple places.  The
> cabal file tells you what is required to build the package, the pragmas
> what is required to build each source file.
>
> Perhaps cabal should complain when source files use pragmas not
> declared in the cabal file, and perhaps also warn about options in the
> cabal file not used in any source file.

The "extensions" field in a cabal package description is a bit tricky.
The documentation states "A list of Haskell extensions used by every
module". This might give the impression that it documents the various
extensions used in a package. What it actually does is enable those
extensions for every module.

Duncan's comments on this ticket are enlightening:
http://hackage.haskell.org/trac/hackage/ticket/370

I think the idea of adding a new field "used-extensions" warrants a
separate ticket.