Add dhallPackages and add current Prelude

Dhall is a non-turing complete programming language.

pkgs/development/dhall-modules/default.nix

@@ -0,0 +1,9 @@
+{ pkgs }:
+
+# TODO: add into the toplevel fixpoint instead of using rec
+rec {
+
+  prelude = prelude_3_0_0;
+  prelude_3_0_0 = pkgs.callPackage ./prelude/v3.nix {};
+
+}

pkgs/development/dhall-modules/prelude/v3.nix

@@ -0,0 +1,25 @@
+{ stdenv, lib, fetchFromGitHub }:
+
+stdenv.mkDerivation {
+  name = "dhall-prelude";
+
+  src = fetchFromGitHub {
+    owner = "dhall-lang";
+    repo = "dhall-lang";
+    # Commit where the v3.0.0 prelude folder was merged into dhall-lang
+    # and a LICENSE file has been added.
+    rev = "f6aa9399f1ac831d66c34104abe6856023c5b2df";
+    sha256 = "0kqjgh3y1l3cb3rj381j7c09547g1vh2dsfzpm08y1qajhhf9vgf";
+  };
+
+  phases = [ "unpackPhase" "installPhase" ];
+
+  installPhase = ''
+    cp -r Prelude $out
+  '';
+
+  meta = {
+    license = lib.licenses.bsd3;
+    maintainers = with lib.maintainers; [ Profpatsch ];
+  };
+}