NixOS newbie: xmonad and haskellmode on NixOS 14.04

Question

I am trying to configure NixOS VM to develop code in haskell and am encountering problems with the basic installation of xmonad and emacs. Relevant part of my/etc/nixos/configuration.nix

environment.systemPackages = with pkgs; [
    emacs
    emacs24Packages.haskellMode
    xlibs.xmessage
    haskellPackages.haskellPlatform.ghc
    haskellPackages.xmobar
    haskellPackages.xmonad
    haskellPackages.xmonadContrib
    haskellPackages.xmonadExtras
];

• xmonad: when I try to compile the code, xmonad complains that it could not find the XMonad.Util.EZConfig module. Compiling xmonad.hswith ghc is fine, and I can also load the module in ghci. On channel #nixos I was told to use the ghcWithPackages function, but I could not fix the problem. Moreover, I would like to understand why this problem primarily arises, since it seems to me that this is a very simple use case. The minimal xmonad.hsone I am having a problem with:

  import XMonad
  import XMonad.Util.EZConfig
  
  main = xmonad $ defaultConfig
    { modMask = mod4Mask
    , terminal = "konsole"
    }
    `additionalKeysP`
    [ ("M-e", spawn "emacs")
    , ("M-f", spawn "firefox")
    ]
  

• emacs: haskellmode ( configuration.nix ), haskell-mode emacs.

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Answer 1

    windowManager.xmonad.enableContribAndExtras = true;

to

    /etc/nixos/configuration.nix

xmonad .xsession

Answer 2

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