Update nix target.

nix/.nixpkgs/config.nix

@@ -0,0 +1,27 @@
+{
+  packageOverrides = super: let self = super.pkgs; in {
+    myHaskellEnv =
+      self.haskell.packages.ghc7102.ghcWithPackages
+          (haskellPackages: with haskellPackages; [
+              aeson
+              arrows
+              async
+              bake
+              cabal-install
+              case-insensitive
+              ghc-mod
+              hindent
+              hoogle
+              hspec
+              inline-c
+              pandoc
+              shake
+              ShellCheck
+              Spock
+              stack
+              stylish-haskell
+              wreq
+              ]
+          );
+  };
+}

nix/.profile.d/20-functions-nix.sh

@@ -6,3 +6,11 @@ mk_nix_shell()
     | sed -E -e 's/(cabal\.mkDerivation)/with haskellPackages; \1/' -e 'sXsha256 = "0";Xsrc = "./.";X' \
           > shell.nix;
 }
+
+nix_env_setup()
+{
+  NIX_GHC=$(type -p ghc > /dev/null 2>&1)
+  if [ -n "$NIX_GHC" ]; then
+    eval $(grep export "$NIX_GHC")
+  fi
+}

nix/.profile.d/99-final-nix.sh

@@ -3,6 +3,9 @@
 # The nix installer put something like this into the .profile.
 # BAD INSTALLER NO COOKIE!
 if [ -e ${HOME}/.nix-profile/etc/profile.d/nix.sh ]; then
-    . ${HOME}/.nix-profile/etc/profile.d/nix.sh;
-    export NIX_PATH=${HOME}/src/github.com/NixOS/nixpkgs:nixpkgs=${HOME}/src/github.com/NixOS/nixpkgs
+  . ${HOME}/.nix-profile/etc/profile.d/nix.sh;
+  export NIX_PATH=${HOME}/src/github.com/NixOS/nixpkgs:nixpkgs=${HOME}/src/github.com/NixOS/nixpkgs
+  export NIX_CFLAGS_COMPILE="-idirafter /usr/include"
+  export NIX_CFLAGS_LINK="-L/usr/lib"
+  nix_env_setup
 fi