[Haskell-cafe] Re: Unable to install packages

[Albert Y. C. Lai]

On 10-11-28 09:55 AM, Ketil Malde wrote:
> Joachim Breitner<mail at joachim-breitner.de>  writes:
>
>> I would not recommend using --global on Debian/Ubuntu-systems, as it
>> might interfere with packages installed by Debian.
>
> But 'cabal install --global' installs in /usr/local/, does it not?
> And official packages (i.e. debs) put stuff in /usr, so these would be
> separate.

Metadata is more important than data.

In the case of Debian/Ubuntu's GHC, both 'cabal install --global' and 
'apt-get install' records in /var/lib/ghc-6.12.3/package.conf.d

If you cabal install one version and apt-get another version, sure, they 
are two different records in the metadata, no immediate problem.

But how about

   cabal install --global binary
   apt-get install libghc6-binary-dev

They are the same version (at the time of writing, and assume Ubuntu 
10.10) and they will fight for the unique throne of "binary-0.5.0.2" in 
the metadata.

The immediate problem: they likely have different ABI hashes because 
they're built differently. Suppose you

   cabal install --global binary
   (suppose it becomes binary-0.5.0.2-300339c66a688207241e4643a9e17721)
   cabal install --global I-depend-on-binary
   apt-get install libghc6-binary-dev
   (this is binary-0.5.0.2-32d59ff8fdfc79aa888e82997612374d in Ubuntu 
10.10 i386 32-bit)

Now I-depend-on-binary is hosed. It was built against 
binary-0.5.0.2-300339c66a688207241e4643a9e17721 but that's usurped.

OK, who would knowingly usurp his/her own binary-0.5.0.2? Of course no 
one knowingly does. But everyone does it unknowingly:

   cabal install --global maccatcher
   (this brings in binary)
   apt-get install libghc6-agda-dev
   (this brings in libghc6-binary-dev)

Now maccatcher is hosed.

See also my http://www.vex.net/~trebla/haskell/sicp.xhtml

P.S. Deleting "--global" mitigates this problem but causes some other 
problem. I will describe it in my article in the future.