can't load .so/.DLL - undefined symbol

[Simon Marlow]

On 11/03/2014 22:11, Henning Thielemann wrote:
> I am trying to understand the following linker message. I have started
> GHCi, loaded a program and try to run it:
>
> Main> main
> ...
> Loading package poll-0.0 ... linking ... done.
> Loading package alsa-seq-0.6.0.3 ... can't load .so/.DLL for:
> /var/cabal/lib/x86_64-linux-ghc-7.8.0.20140228/alsa-seq-0.6.0.3/libHSalsa-seq-0.6.0.3-ghc7.8.0.20140228.so
> (/var/cabal/lib/x86_64-linux-ghc-7.8.0.20140228/alsa-seq-0.6.0.3/libHSalsa-seq-0.6.0.3-ghc7.8.0.20140228.so:
> undefined symbol:
> alsazmseqzm0zi6zi0zi3_SystemziPosixziPoll_zdfStorableFd_closure)
>
>
> I assume that GHCi wants to say the following: The instance Storable Fd
> defined in module System.Posix.Poll cannot be found in the shared object
> file of the alsa-seq package. That's certainly true because that module
> is in the package 'poll' and not in 'alsa-seq'. But 'alsa-seq' imports
> 'poll'. What might be the problem?

It seems to have the idea that System.Posix.Poll is part of the alsa-seq 
package.  Perhaps you have a copy of that module on the search path 
somewhere, or inside the alsa-seq package?

Cheers,
Simon


> It's a rather big example that fails here, whereas the small examples in
> alsa-seq package work. Thus I first like to know what the message really
> means, before investigating further. I installed many packages at once
> with cabal-install using a single build directory, like:
>
> $ cabal install --builddir=/tmp/dist --with-ghc=ghc7.8.0.20140228 poll
> alsa-seq pkg1 pkg2 pkg3 ...
>
> ? Can this cause problems?
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