haskell-transformers-compat: provide different versions for GHC 7.8.2…

… and below

transformers is a core library in GHC 7.8.2, so that compiler is stuck
with an older version of the -compat library.

pkgs/development/libraries/haskell/transformers-compat/0.3.3.nix

@@ -0,0 +1,14 @@
+{ cabal, transformers }:
+
+cabal.mkDerivation (self: {
+  pname = "transformers-compat";
+  version = "0.3.3";
+  sha256 = "14lmwqr6q79k1f7byvb0jcm4r7lprhxkl85z72pr6ghn7bsvqwps";
+  buildDepends = [ transformers ];
+  meta = {
+    homepage = "http://github.com/ekmett/transformers-compat/";
+    description = "A small compatibility shim exposing the new types from transformers 0.3 and 0.4 to older Haskell platforms.";
+    license = self.stdenv.lib.licenses.bsd3;
+    platforms = self.ghc.meta.platforms;
+  };
+})

pkgs/top-level/haskell-defaults.nix

@@ -17,6 +17,7 @@
   ghcHEADPrefs = self : super : super // {
     mtl = self.mtl_2_1_2;
     cabalInstall_1_20_0_2 = super.cabalInstall_1_20_0_2.override { Cabal = null; };
+    transformersCompat = super.transformersCompat_0_3_3;
   };
 
   ghc782Prefs = self : super : ghcHEADPrefs self super // {
@@ -44,6 +45,7 @@
     mtl = self.mtl_2_2_1;
     pipesBinary = super.pipesBinary.override { binary = self.binary_0_7_2_1; };
     transformers = self.transformers_0_4_1_0; # core packagen in ghc > 7.6.x
+    transformersCompat = super.transformersCompat;
     zipArchive = super.zipArchive_0_2_2_1;    # works without binary 0.7.x
   };
 

pkgs/top-level/haskell-packages.nix

@@ -2269,7 +2269,9 @@ self : let callPackage = x : y : modifyPrio (newScope self x y); in
 
   transformersBase = callPackage ../development/libraries/haskell/transformers-base {};
 
-  transformersCompat = callPackage ../development/libraries/haskell/transformers-compat {};
+  transformersCompat_0_3_3 = callPackage ../development/libraries/haskell/transformers-compat/0.3.3.nix {};
+  transformersCompat_0_3_3_4 = callPackage ../development/libraries/haskell/transformers-compat/0.3.3.4.nix {};
+  transformersCompat = self.transformersCompat_0_3_3_4;
 
   transformersFree = callPackage ../development/libraries/haskell/transformers-free {};