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I'm currently trying to use pandoc (as a Haskell module, not as a program) to convert MediaWiki text to other formats.

Let's assume this program:

 import Text.Pandoc.Readers.MediaWiki
 main = do print "foo"

When using runghc to run it, I get the following error message:

pandock.hs:1:8:
    Could not find module `Text.Pandoc.Readers.MediaWiki'
    Use -v to see a list of the files searched for.

My first assumption was that pandoc was either not installed or incorrectly installed. Therefore I reinstalled it with --force-reinstalls

$ cabal install pandoc --reinstall
[...]
In order, the following will be installed:
pandoc-1.12.3.1 (reinstall) changes: old-time-1.1.0.1 added
[...]
[32 of 55] Compiling Text.Pandoc.Readers.MediaWiki ( src/Text/Pandoc/Readers/MediaWiki.hs, dist/build/Text/Pandoc/Readers/MediaWiki.o )
[...]
Installing library in
/home/uli/.cabal/lib/x86_64-linux-ghc-7.6.3/pandoc-1.12.3.1
Installing executable(s) in /home/uli/.cabal/bin
Registering pandoc-1.12.3.1...
Installed pandoc-1.12.3.1

The output of runghc -v pandock.hs is quite long, I assume the relevant part is:

*** Chasing dependencies:
Chasing modules from: *pandock.hs

pandock.hs:1:8:
    Could not find module `Text.Pandoc.Readers.MediaWiki'
    Locations searched:
      Text/Pandoc/Readers/MediaWiki.hs
      Text/Pandoc/Readers/MediaWiki.lhs
Failed, modules loaded: none.

However, both ~/.cabal/lib/x86_64-linux-ghc-7.6.3/pandoc-1.12.3.1/Text/Pandoc/Readers/Mediawiki/MediaWiki.hi and ~/.cabal/bin/pandoc exist. How can I make GHC properly recognize the cabal-installed package?

Any help will be appreciated!

Uli Köhler
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  • Is your installation of pandoc in the global or user package database? I believe that `runghc` only looks in one of those databases. – user2407038 Jan 22 '14 at 04:32
  • @user2407038 I didn't install with `cabal install --global`, so can I assume it's in the user DB? I installed and regularly use dozends of other packages the same way (`cabal install pandoc`), there is no problem with any of those (including, for example Yesod). – Uli Köhler Jan 22 '14 at 04:36
  • At the location where `pandock.hs` is located and you're invoking `runghc`, do you by chance have subdirectories called `Text` and `Text/Pandoc`? – kosmikus Jan 22 '14 at 08:18
  • @kosmikus Unfortunately, no :-( It it an empty directory (I specifically take care of that because I had similar problems with Python not finding Tornado because the file was named tornado.py) – Uli Köhler Jan 23 '14 at 01:00
  • @MigMit Yes, it does (`ghc-pkg list | grep pandoc` yields `pandoc-1.12.3.1`). I'm currently facing the exact same issues with the `yaml` package, so it doesn't seem to be specific to `pandoc`. I also tried without any success to reproduce the problem on another computer. `ghc-pkg check` shows some broken packages, maybe the problem is related to them? – Uli Köhler Jan 23 '14 at 01:02

1 Answers1

2

When trying to reproduce this issue on other computers, only 2 out of 5 computers had this issue. On both of them I installed cabal packages in about the same way and order.

In retrospect I assume this issue arose because of some broken packages wreaking havoc:

$ ghc-pkg check
There are problems in package feed-0.3.9.2:
  dependency "xml-1.3.13-dd52b1688e97a3c6cd0aa48dba7b153e" doesn't exist
There are problems in package hxt-9.3.1.3:
  dependency "network-2.4.2.2-ea77cdf1bc747bc58308fdeb52745c4d" doesn't exist
There are problems in package hspec-1.8.1.1:
  dependency "QuickCheck-2.6-409fcc32c191cd6e04afdebb15869820" doesn't exist
There are problems in package quickcheck-io-0.1.0:
  dependency "QuickCheck-2.6-409fcc32c191cd6e04afdebb15869820" doesn't exist
There are problems in package regex-compat-0.95.1:
  dependency "regex-base-0.93.2-2023953b859e6f91efe89733d2ef5421" doesn't exist
There are problems in package regex-posix-0.95.2:
  dependency "regex-base-0.93.2-2023953b859e6f91efe89733d2ef5421" doesn't exist
There are problems in package hxt-9.3.1.2:
  dependency "network-2.4.2.2-ea77cdf1bc747bc58308fdeb52745c4d" doesn't exist

The following packages are broken, either because they have a problem
listed above, or because they depend on a broken package.
feed-0.3.9.2
hxt-9.3.1.3
hspec-1.8.1.1
quickcheck-io-0.1.0
regex-compat-0.95.1
regex-posix-0.95.2
hxt-9.3.1.2
MissingH-1.2.0.2
yesod-test-1.2.1

Note that neither pandoc nor yaml (I installed it after asking the question and had the exact same issues as with pandoc) are listed there.

For users also having a similar problem, please ensure:

  1. The package is installed and you're not inside any sandbox where the package is not installed.

  2. In the directory where you're executing the test script, ensure that there is no Text/Pandoc folder (or equivalent, depending on the package causing the problem

  3. Run your test script with runghc -v to check if it searches the proper directory

  4. ghc-pkg list lists your package as installed, and no packages are broken (use ghc-pkg check to check)

I solved my problem by renaming ~/.cabal and ~/.ghc. Note that I did this lacking a proper solution, I think you should only do this as a last resort.

Uli Köhler
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