Add shell.nix

shell.nix

@@ -0,0 +1,52 @@
+{ nixpkgs ? import <nixpkgs> {}, compiler ? "default", doBenchmark ? false }:
+
+let
+
+  inherit (nixpkgs) pkgs;
+
+  f = { mkDerivation, ansi-wl-pprint, base, containers, criterion
+      , data-fix, deepseq, deriving-compat, directory, filepath, Glob
+      , parsers, regex-tdfa, regex-tdfa-text, semigroups, split, stdenv
+      , tasty, tasty-hunit, tasty-th, text, transformers, trifecta
+      , unordered-containers, these, optparse-applicative, free
+      , interpolate, process, exceptions, bytestring, mtl, monadlist
+      , base16-bytestring, cryptohash, template-haskell, syb
+      }:
+      mkDerivation {
+        pname = "hnix";
+        version = "0.4.0";
+        src = ./.;
+        isLibrary = true;
+        isExecutable = true;
+        libraryHaskellDepends = [
+          ansi-wl-pprint base containers data-fix deepseq deriving-compat
+          parsers regex-tdfa regex-tdfa-text semigroups text transformers
+          trifecta unordered-containers these free process directory
+          filepath exceptions bytestring mtl monadlist base16-bytestring
+          cryptohash template-haskell syb
+        ];
+        executableHaskellDepends = [
+          ansi-wl-pprint base containers data-fix deepseq optparse-applicative
+          text transformers unordered-containers template-haskell
+        ];
+        testHaskellDepends = [
+          base containers data-fix directory filepath Glob split tasty
+          tasty-hunit tasty-th text transformers interpolate
+        ];
+        benchmarkHaskellDepends = [ base containers criterion text ];
+        homepage = "http://github.com/jwiegley/hnix";
+        description = "Haskell implementation of the Nix language";
+        license = stdenv.lib.licenses.bsd3;
+      };
+
+  haskellPackages = if compiler == "default"
+                       then pkgs.haskellPackages
+                       else pkgs.haskell.packages.${compiler};
+
+  variant = if doBenchmark then pkgs.haskell.lib.doBenchmark else pkgs.lib.id;
+
+  drv = variant (haskellPackages.callPackage f {});
+
+in
+
+  if pkgs.lib.inNixShell then drv.env else drv