Add expression for Haskell library 'these'

pkgs/development/libraries/haskell/these/default.nix

@@ -0,0 +1,19 @@
+{ cabal, bifunctors, mtl, profunctors, semigroupoids, semigroups
+, transformers, vector
+}:
+
+cabal.mkDerivation (self: {
+  pname = "these";
+  version = "0.4.2";
+  sha256 = "0hs59i07k1lkynvdpymjvl1va2frc3aq6wyrmbi7mz3vmz0bjcp7";
+  buildDepends = [
+    bifunctors mtl profunctors semigroupoids semigroups transformers
+    vector
+  ];
+  meta = {
+    homepage = "https://github.com/isomorphism/these";
+    description = "An either-or-both data type, with corresponding hybrid error/writer monad transformer";
+    license = self.stdenv.lib.licenses.bsd3;
+    platforms = self.ghc.meta.platforms;
+  };
+})