add Nix expression for static/cross compilation

.gitignore

@@ -1,2 +1 @@
 dist
-default.nix

default.nix

@@ -0,0 +1,47 @@
+{ nixpkgs ? <nixpkgs>
+, static ? false
+, compiler ? "default"
+, doBenchmark ? false
+, system ? builtins.currentSystem
+}:
+
+let
+
+  basepkgs = import nixpkgs { inherit system; };
+  pkgs = if static then basepkgs.pkgsStatic else basepkgs.pkgs;
+
+  f = { mkDerivation, base, bytestring, configurator, data-default
+      , directory, exceptions, filepath, leveldb-haskell, mtl, selda
+      , selda-sqlite , lib, text, snappy
+      }:
+      mkDerivation {
+        pname = "bisc";
+        version = "0.3.0.0";
+        src = ./.;
+        isLibrary = false;
+        isExecutable = true;
+        executableHaskellDepends = [
+          base bytestring configurator data-default directory exceptions
+          filepath leveldb-haskell mtl selda selda-sqlite text
+        ];
+        executableSystemDepends = [ snappy ];
+        buildFlags = lib.optionals static [
+          "--ld-option=-lstdc++"
+          "--ld-option=-lsnappy"
+        ];
+        homepage = "https://maxwell.ydns.eu/git/rnhmjoj/bisc";
+        description = "A small tool that clears cookies (and more)";
+        license = lib.licenses.gpl3;
+      };
+
+  ghc =  if static then pkgs.haskell.packages.integer-simple.ghc8104
+    else 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 (ghc.callPackage f {});
+
+in
+
+  if pkgs.lib.inNixShell then drv.env else drv