Libraries Digest, Vol 87, Issue 16

John Lato jwlato at
Wed Nov 10 05:31:46 EST 2010

On Tue, Nov 9, 2010 at 5:12 PM, Duncan Coutts
<duncan.coutts at>wrote:

> On 9 November 2010 10:40, John Lato <jwlato at> wrote:
> >> On the other hand, on those systems people would get all packages
> >> (libraries and programs) required by the Haskell platform, plus
> >> some additional ones. Wouldn't hurt too much, IMHO (allthough it
> >> feels a little bit wrong if the platform would contain programs
> >> that can't be built with only the platform).
> >
> > I think this was exactly the situation rationale 8.5 means to avoid.
> > I do think it would be technically possible to make this work, but only
> by
> > greatly increasing the maintenance cost for HP (I underestimated this
> cost
> > originally).  It's probably not a good trade-off.
> > If cabal supported something like run-time-specified repos it would be
> much simpler.
> What sort of thing are you thinking of here?

If, in addition to the global and user package stores, you could specify
alternate package stores.  Then it would be possible to do e.g.

cabal install --use-package-store=./buildlibs

to create a package store at ./buildlibs (if it doesn't exist) and install a
library there.  Then later commands could do

cabal install --extra-package-store=./buildlibs

to check for packages in that extra location in addition to the default
global and user locations.

This would certainly enable building non-blessed libs as part of the HP and
differentiating from the normal blessed packages.  It might be useful for
other reasons too.  I'm not saying it's a good idea for HP, just that it
would be technically possible.

Were some other people already talking about this in this thread?  Is this
already implemented?

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