Add Dhall preludes

dhall/default.nix

@@ -0,0 +1,8 @@
+{ nixpkgs }:
+
+rec {
+
+  prelude = prelude_9_0_0;
+  prelude_9_0_0 = nixpkgs.callPackage ./prelude-9.0.0.nix {};
+  genode = nixpkgs.callPackage ./genode.nix {};
+}

dhall/genode.nix

@@ -0,0 +1,7 @@
+{ fetchgit }:
+
+fetchgit
+  { url = "git://depot.h4ck.me/srv/git/dhall-genode";
+    rev = "4b03fc71a4529cc35cef9dfe9d95ec431f8246e6";
+    sha256 = "0a2ff2d68yxvg2vwdbigakglixxbw063bays0mg9hkbd8570l3h3";
+  }

dhall/prelude-9.0.0.nix

@@ -0,0 +1,24 @@
+{ stdenvNoCC, lib, fetchFromGitHub }:
+
+stdenvNoCC.mkDerivation {
+  name = "dhall-prelude";
+  version = "9.0.0";
+
+  src = fetchFromGitHub {
+    owner = "dhall-lang";
+    repo = "dhall-lang";
+    rev = "6cbf57c946e7e6576babc23a38320e53ecfa6bee";
+    sha256 = "1r06fijszyifq5b4j6libwkm06g8693m9n5c4kq61dvzrjfd2gim";
+  };
+
+  phases = [ "unpackPhase" "installPhase" ];
+
+  installPhase = ''
+    cp -r Prelude $out
+  '';
+
+  meta = {
+    license = lib.licenses.bsd3;
+    maintainers = with lib.maintainers; [ ehmry ];
+  };
+}