[Nix-dev] fixing ghc-pkg update

[roconnor at theorem.ca]

It turns out that this bug is won't fix:  See 
<http://hackage.haskell.org/trac/ghc/ticket/4884#comment:2>

I was afraid of this.  This means that the ghc-pkg wrapper doesn't really work 
in NixOS.

Or, is this specifically the way that NixOS is designed?

Am I not supposed to be doing user installs of software that depend on nix 
installs of software, because without nixos tracking the softare, the 
dependencies could get uninstalled and garbage collected, breaking the user 
installed software.  Is this specifically disallowed?

Are users expected to write nix expressions for all the local software they 
wish to install?

Arguably the same problems noted above apply to Ubuntu.  When apt is managing a 
haskell package, then user installed packages will break when an apt managed 
haskell package is upgraded or deleted.  But then again, maybe we are aiming to 
do better than apt here?

How does this compare to building C programs?  I can locally build C programs 
depending on nix-managed dependences.  So these programs will break if nix 
updates or deletes dependencies.  OTOH there is really no signifigant "install" 
step for C programs.  Arguable I can build Haskell programs just like C 
programs.  I just can't user install Haskell programs using cabal.

So ultimately my question is, should we investgate hacking ghc-pkg to allow 
users to install software depending on nix-managage pacakges, or do we want 
that to be disallowed for some reason?

-- 
Russell O'Connor                                      <http://r6.ca/>
``All talk about `theft,''' the general counsel of the American Graphophone
Company wrote, ``is the merest claptrap, for there exists no property in
ideas musical, literary or artistic, except as defined by statute.''