Re: [Haskell-beginners] Cabal: Upgrading to the latest version of library

On Wed, Nov 2, 2011 at 1:31 AM, Giovanni Tirloni wrote:

On Tue, Nov 1, 2011 at 2:04 PM, Hugo Ferreira wrote:

...

I have used Ocaml + the GODI "package manager" and it seems work ok. GODI allows one to identify newer packages, select those we want to upgrade and recompiles any dependencies automatically.

As a newcommer, I feel that this subject has already been discussed at length by the Haskell community and progress is being made.

Two articles that I have been referred to in order to understand it better:

http://www.vex.net/~trebla/haskell/sicp.xhtml#unsafeInterleave

http://ivanmiljenovic.wordpress.com/2010/03/15/repeat-after-me-cabal-is-not-...

Thanks for those links.

As a Fedora user, I'm relying on the Haskell SIG work and using the ghc-* RPM packages. When a given Hackage package has not been packaged in Fedora yet, I'm using cabal to supplement but I think that's sub-optimal (from a sysadmin perspective). I'm looking at ways to actually build my own RPMs following their standards. As it's mentioned in one of the article, someone has had the trouble to figure out which packages work best together.

I wonder if you could throw some light on this? Say you just have to use the 'sub-optimal' solution and cabal install some package foo. Later it appears in the rpm list and you can yum install it. How do you now cabal uninstall foo?

I second Daniel's opinion that updates should be a conscious decision on the part of the developer. The kind of dependency problems exemplified are not restricted to cabal and apply as well to PHP's Pear, Perl's CPAN and others. What I usually see is that developers try to guarantee their packages will correctly work with a given set of dependencies and so they specify minimum and maximum versions of those as restrictions. Obviously, easing those restrictions would ensure it's easier to match package but who guarantees they'll work (i.e. no important API change) ?

My own experience managing packages in PHP hosting environments tells me that, even though the package manager was happy to upgrade everything I told it to.. I would usually find the interfacing problems myself in the form of downtime. In that scenario, I would prefer both a package more strictly defined in terms of dependencies. In cabal/Haskell things won't even compile, which is good :-)

Any, just 0.02 from a newbie.

Giovanni

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