title: Leksah in NixOS 14.12 - fails to install, why?
body: <p>Leksah in NixOS 14.12 - unstable channel fails to install, why ?</p>
  
  <pre><code>[demo@nixos:~]$ nix-channel --list
  nixpkgs http://nixos.org/channels/nixpkgs-unstable
  
  [demo@nixos:~]$ nix-env -i leksah
  installing ‘leksah’
  these derivations will be built:
    /nix/store/69k8c7mvz64k08z9gabh7gmcn1i265rn-haskell-regex-tdfa-text-1.0.0.2.drv
    /nix/store/h9dxxnab1sngr2d6g1q9qj0yv35iqyzs-haskell-leksah-0.15.0.1.drv
    /nix/store/lfjh66d015dkh9kr51h5871c7gqji5na-ghc-7.10.1.drv
    /nix/store/pdpsxp33mffmq72vhk5ig8bhrrdyq7p2-leksah.drv
  building path(s) ‘/nix/store/53kxzd2apkijwib78gw4mdlpxs5vllpj-haskell-regex-tdfa-text-1.0.0.2’
  setupCompilerEnvironmentPhase
  Build with /nix/store/bc84hdk730zcdm1c9s5yf2ahpvm51lzp-ghc-7.10.1.
  unpacking sources
  unpacking source archive /nix/store/cmrcmadl401k7sjgqwj2dz4b9jqwxnck-regex-tdfa-text-1.0.0.2.tar.gz
  source root is regex-tdfa-text-1.0.0.2
  patching sources
  compileBuildDriverPhase
  setupCompileFlags: -package-db=/tmp/nix-build-haskell-regex-tdfa-text-1.0.0.2.drv-0/package.conf.d -j1 -threaded
  [1 of 1] Compiling Main             ( Setup.lhs, /tmp/nix-build-haskell-regex-tdfa-text-1.0.0.2.drv-0/Main.o )
  Linking Setup ...
  configuring
  configureFlags: --verbose --prefix=/nix/store/53kxzd2apkijwib78gw4mdlpxs5vllpj-haskell-regex-tdfa-text-1.0.0.2 --libdir=$prefix/lib/$compiler --libsubdir=$pkgid --with-gcc=gcc --package-db=/tmp/nix-build-haskell-regex-tdfa-text-1.0.0.2.drv-0/package.conf.d --ghc-option=-optl=-Wl,-rpath=/nix/store/53kxzd2apkijwib78gw4mdlpxs5vllpj-haskell-regex-tdfa-text-1.0.0.2/lib/ghc-7.10.1/regex-tdfa-text-1.0.0.2 --ghc-option=-j1 --enable-split-objs --disable-library-profiling --enable-shared --enable-library-vanilla --enable-executable-dynamic --enable-tests
  Configuring regex-tdfa-text-1.0.0.2...
  Dependency array -any: using array-0.5.1.0
  Dependency base &gt;=3 &amp;&amp; &lt;5: using base-4.8.0.0
  Dependency regex-base -any: using regex-base-0.93.2
  Dependency regex-tdfa &gt;=1.1.1: using regex-tdfa-1.2.0
  Dependency text -any: using text-1.2.1.1
  Using Cabal-1.22.2.0 compiled by ghc-7.10
  Using compiler: ghc-7.10.1
  Using install prefix:
  /nix/store/53kxzd2apkijwib78gw4mdlpxs5vllpj-haskell-regex-tdfa-text-1.0.0.2
  Binaries installed in:
  /nix/store/53kxzd2apkijwib78gw4mdlpxs5vllpj-haskell-regex-tdfa-text-1.0.0.2/bin
  Libraries installed in:
  /nix/store/53kxzd2apkijwib78gw4mdlpxs5vllpj-haskell-regex-tdfa-text-1.0.0.2/lib/ghc-7.10.1/regex-tdfa-text-1.0.0.2
  Private binaries installed in:
  /nix/store/53kxzd2apkijwib78gw4mdlpxs5vllpj-haskell-regex-tdfa-text-1.0.0.2/libexec
  Data files installed in:
  /nix/store/53kxzd2apkijwib78gw4mdlpxs5vllpj-haskell-regex-tdfa-text-1.0.0.2/share/x86_64-linux-ghc-7.10.1/regex-tdfa-text-1.0.0.2
  Documentation installed in:
  /nix/store/53kxzd2apkijwib78gw4mdlpxs5vllpj-haskell-regex-tdfa-text-1.0.0.2/share/doc/x86_64-linux-ghc-7.10.1/regex-tdfa-text-1.0.0.2
  Configuration files installed in:
  /nix/store/53kxzd2apkijwib78gw4mdlpxs5vllpj-haskell-regex-tdfa-text-1.0.0.2/etc
  No alex found
  Using ar found on system at:
  /nix/store/yxg5zsjxp1l16xk7r23rayyc18fkxynk-binutils-2.23.1/bin/ar
  No c2hs found
  No cpphs found
  Using gcc version 4.8.4 given by user at:
  /nix/store/ylj1q31a7x3pvcraxk60dyv9y4wmwcrc-gcc-wrapper-4.8.4/bin/gcc
  Using ghc version 7.10.1 found on system at:
  /nix/store/bc84hdk730zcdm1c9s5yf2ahpvm51lzp-ghc-7.10.1/bin/ghc
  Using ghc-pkg version 7.10.1 found on system at:
  /nix/store/bc84hdk730zcdm1c9s5yf2ahpvm51lzp-ghc-7.10.1/bin/ghc-pkg
  No ghcjs found
  No ghcjs-pkg found
  No greencard found
  Using haddock version 2.16.0 found on system at:
  /nix/store/bc84hdk730zcdm1c9s5yf2ahpvm51lzp-ghc-7.10.1/bin/haddock
  No happy found
  Using haskell-suite found on system at: haskell-suite-dummy-location
  Using haskell-suite-pkg found on system at: haskell-suite-pkg-dummy-location
  No hmake found
  Using hpc version 0.67 found on system at:
  /nix/store/bc84hdk730zcdm1c9s5yf2ahpvm51lzp-ghc-7.10.1/bin/hpc
  Using hsc2hs version 0.67 found on system at:
  /nix/store/bc84hdk730zcdm1c9s5yf2ahpvm51lzp-ghc-7.10.1/bin/hsc2hs
  Using hscolour version 1.22 found on system at:
  /nix/store/g6mfdhbmwm0499n88bnzd32y96gmnfn9-hscolour-1.23/bin/HsColour
  No jhc found
  Using ld found on system at:
  /nix/store/ylj1q31a7x3pvcraxk60dyv9y4wmwcrc-gcc-wrapper-4.8.4/bin/ld
  No lhc found
  No lhc-pkg found
  No pkg-config found
  Using strip version 2.23 found on system at:
  /nix/store/yxg5zsjxp1l16xk7r23rayyc18fkxynk-binutils-2.23.1/bin/strip
  Using tar found on system at:
  /nix/store/blyc5sprbm85ph2fmksyhrqislp9j0im-gnutar-1.28/bin/tar
  No uhc found
  building
  Building regex-tdfa-text-1.0.0.2...
  Preprocessing library regex-tdfa-text-1.0.0.2...
  [1 of 2] Compiling Text.Regex.TDFA.Text.Lazy ( Text/Regex/TDFA/Text/Lazy.hs, dist/build/Text/Regex/TDFA/Text/Lazy.o )
  
  Text/Regex/TDFA/Text/Lazy.hs:77:9:
      Non type-variable argument
        in the constraint: Data.Array.Base.IArray a (Int, Int)
      (Use FlexibleContexts to permit this)
      When checking that ‘go’ has the inferred type
        go :: forall t (a :: * -&gt; * -&gt; *) i.
              (Functor (a i), Num i, GHC.Arr.Ix i,
               Data.Array.Base.IArray a (Int, Int), Extract t) =&gt;
              Int -&gt; t -&gt; [a i (Int, Int)] -&gt; [a i (t, (Int, Int))]
      In the expression:
        let
          go i _ _ | i `seq` False = undefined
          go _i _t [] = []
          go i t (x : xs)
            = let ... in fmap trans x : seq t' (go (off0 + len0) t' xs)
        in go 0 source (matchAll regex source)
      In an equation for ‘matchAllText’:
          matchAllText regex source
            = let
                go i _ _ | i `seq` False = undefined
                go _i _t [] = ...
                go i t (x : xs) = ...
              in go 0 source (matchAll regex source)
  builder for ‘/nix/store/69k8c7mvz64k08z9gabh7gmcn1i265rn-haskell-regex-tdfa-text-1.0.0.2.drv’ failed with exit code 1
  cannot build derivation ‘/nix/store/lfjh66d015dkh9kr51h5871c7gqji5na-ghc-7.10.1.drv’: 1 dependencies couldn't be built
  cannot build derivation ‘/nix/store/pdpsxp33mffmq72vhk5ig8bhrrdyq7p2-leksah.drv’: 1 dependencies couldn't be built
  error: build of ‘/nix/store/pdpsxp33mffmq72vhk5ig8bhrrdyq7p2-leksah.drv’ failed
  </code></pre>