I have written a new eclass, to be called ghc-package.eclass,
and submitted it as bug #69270 for everyone to see.

Explanation for non-Haskellers:

The Glasgow Haskell Compiler (GHC) is available in Gentoo
as an ebuild (dev-lang/ghc).

There are also a couple of Haskell libraries in the distribution,
and there are going to be more in the future ... For a library
to be available for other Haskell programs to use, it has to be
registered with GHC's package tool, called ghc-pkg, which is
shipped with the compiler.

This package tool writes a system-wide package configuration file,
and can therefore only be executed during post-installation.

Currently, the Haskell libraries that have ebuilds use slightly
varying hacks to prevent the makefiles from calling ghc-pkg
directly and to register the packages during post-installation
(and to unregister packages during removal).

This is the main purpose that the eclass fulfills: it specifies
clearly what the package maintainer has to do, and it leaves
all the dirty work to the eclass methods.

I have adapted a few ebuilds to use the eclass -- they are
also included in the bug. It seems to work fine.

I am away for the weekend, which gives you time to send comments
and flames. If I don't hear anything negative, I would commit
the eclass next week, and start to convert ebuilds to use it
afterwards ...

Cheers,
  ks

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