Xmonad can't find module XMonad (or any other)

Question

Whenever xmonad starts, restarts, or is recompiled, I get an xmessage:

xmonad.hs:1:8:
Could not find module `XMonad'
 Perhaps you meant
    Monad (needs flag -package haskell98-2.0.0.2)
    CgMonad (needs flag -package ghc-7.6.3)
    DsMonad (needs flag -package ghc-7.6.3)
 Use -v to see a list of the files searched for

This doesn't stop it from starting, but I only see updates to xmonad or xmobar settings on system reboot. My current xmonad.hs is just

import XMonad

main = xmonad defaultConfig

and it still produces the error. Any attempts to import other modules give similar results. I have both xmonad and xmonad-contrib installed from the Arch repositories, so the modules should be properly in the ghc search path, right? I've tried reinstalling the packages from Cabal like some other sources have suggested, but it turned into a complete snafu, so I went back to the Arch repos, which ought to work. Kind of at a loss for where to go from here; any help would be greatly appreciated.

EDIT: ghc-pkg list xmonad returns

/usr/lib/ghc-7.6.3/packag.conf.d
    xmonad-0.11
/home/decalis/.ghc/x86_64-linux-7.6.3/package.conf.d

and ghc-pkg check output is here: http://pastebin.com/BsCPMn8M. The issue is a little clearer after seeing that, but I still don't get why it's looking in ~/.cabal when all of the packages and their dependencies were resolved from the Arch repos by pacman.

Please show the output of ghc-pkg list xmonad and ghc-pkg check — Roman Cheplyaka
No, that looks normal. Do you have any other ghc versions installed? Did you create any sandboxes? Try removing (or renaming) the ~/.cabal and ~/.ghc directories and see if that helps. Check whether you have any other xmonad binaries in your $PATH. — Roman Cheplyaka
Removing ~/.ghc seems to have fixed all of the aberrant behavior. Restarting XMonad works smoothly, settings update appropriately, and ghc-pkg check now only complains about Haddock (which it always has). Thanks for the help! If you want to post that as an answer, I'll accept it. — Decalis
If only I knew why that fixed the problem! From the data you posted it doesn't look like your global xmonad was shadowed by the local one, or anything like that. Ok, I'll post some general advice about such problems. — Roman Cheplyaka

Roman Cheplyaka Roman Cheplyaka · Accepted Answer · 2014-03-14T22:09:56

In cases like this one of the first things to try is to "start from scratch", i.e. forget about all the local packages that you might have installed in the past.

To do this, wipe (or rename/move) ghc's package database, which is under ~/.ghc/$arch-$os-$ghcver (such as ~/.ghc/i386-linux-7.6.3). Or just remove ~/.ghc altogether.

Xmonad can't find module XMonad (or any other)

2 Answers