[Haskell-cafe] I do not want to be a bitch, but ghc-6.8.3 and haskell binary policy are really horrible.

Thomas Schilling nominolo at googlemail.com
Tue Oct 14 06:46:45 EDT 2008

2008/10/14 Magicloud <magicloud.magiclouds at gmail.com>:
> Sorry, let me say it this way:
> 1. Ghc cannot be bootstrap-installed. And the ghc-6.8.3 binary from official
> website also cannot run in my box, some kind of overflow error. So I have to
> look for help, a few hours later, I found 6.4.2 (I am not sure) which runs
> well in my box, and install ghc-6.8.3 indirectly.

Hm, the only issue with binary installers I had were old versions of
some libraries which could be resolved by adding a few symlinks.  What
system are you on?

> 2. After `cabal update && cabal upgrade`, ghc-6.8.3 cannot be built.

Which version of cabal-install ( cabal --version ) are you using?
Note that 'cabal upgrade' is not guaranteed to work since libraries on
hackage don't always specify their dependencies correctly and older
versions of cabal-install might have some issues.  There's an ongoing
initiative to have a set of more controlled packages, the Haskell
Platform.  It should soon has its first release.

That said, you shouldn't need to upgrade anything if you want to build
ghc 6.8.3 with 6.4.2.  Also, what version of ghc does you distribution

> Lib
> Network.URI cannot be compiled because:
> Network/CGI/Protocol.hs:41:0:
>  Failed to load interface for `Network.URI':
>    Perhaps you haven't installed the profiling libraries for package
> network-
>    Use -v to see a list of the files searched for.
> I remove this SUBDIRS from the Makefile, luckly, it works. A few more hours
> lost in my life.
> 3. When I `ghc -v`, there are lots of "hiding package xxx to avoid conflict
> with later version yyy", do I have a way to remove these hiding packages?
> And "package xx will be ignored due to missing or recursive dependencies:
> yy", what does this mean? If it is ignored, my program using it compiled and
> run well. If the dependencies are not right, how can I fix it? I installed
> this by cabal. It reports nothing wrong and cannot check if all packages
> dependencies are OK.
> 4. When `cabal upgrade`, I do not think it knows what it is doing. There
> were many times that I cannot upgrade because I should manually reinstall
> some packages to make it work (Some guy say that this is because ghc cannot
> know the difference between two lib files with the same name). And, cabal
> does not upgrade all packages, I do not know why.

The issue is binary compatibility.  At the moment, GHC cannot make
sure that a library compiled with an older GHC can work with a newer
GHC.  GHC does many cross-module optimisations, and its runtime system
changes occasionally, so it is very pessimistic in that regard.  This
becomes an issue for packages that GHC has been build with itself
(like base, process, array), since these cannot be upgraded without
recompiling GHC (hence requiring recompiling every other package).
Older versions of cabal-install could not deal with this correctly.
So in short, "cabal upgrade" (without arguments) is probably not very
safe, atm.

There are ongoing efforts to provide more ABI compatibility
guarantees, but that requires solving of some difficult issues, so
we're not there yet.

There are certainly some things that could be improved.  For example
GHC 6.10 won't let you unregister a package that other packages depend
on and it keeps checksums of the ABI which may be used by future
versions of Cabal/cabal-install.

> 5. Sometimes when I upgrade some libraries, ghc failed to compile, because
> ld failed to find the new libraries. (Which proves that ghc cannot deal with
> binary files right). I need to recompile this, and recompile that, MAYBE it
> would be resolved.

Without further details I can just guess, but I think this is related
to the problems with binary compatibility above.

> Everyday, I spend a few hours on compiling. Does it really need to be so
> terrible? With erlang or ruby, I never spend more time debugging as
> haskell's feature says but less time on how to run my code.

Many projects can just be loaded via ghci which is a lot faster.  Just
cd to the toplevel source directory, type :l ModuleName.  Then edit
the source code, and type :r to reload the current module.

With many of these smaller issues you can often find quick help on
Haskell's IRC channel #haskell or #ghc if you have problems specific
to GHC (although asking at #haskell will often give you an answer more
quickly, so ask there first anyway)



> Thomas Schilling wrote:
>> It would be helpful if you could describe exactly what you did so we
>> can work on improving the issue in the long term (and help you fix it
>> in the short term).
>> 2008/10/14 Magicloud <magicloud.magiclouds at gmail.com>:
>>> 1. I cannot install ghc-6.8.3 in my box until I found the old runable
>>> binary.
>>> 2. After I installed cabal, and upgraded, ghc-6.8.3 cannot rebuild
>>> itself.
>>> Because its libraries are conflict with the ones upgraded by cabal.
>>> 3. Sometimes, ghc just ignore some libs, because it does not meet its
>>> dependencies. Well, ghc does not even tell me. It knows what I want?
>>> 4. I use cabal, thinking it would make dependencies installation easier
>>> for
>>> me. Well it does not, once an error happened, nothing would work since. I
>>> cannot even remove the broken lib.
>>> 5. No more needed. The above ones, which are important enough to drive me
>>> crazy.
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