beamPackages: Add support for Mix and Erlang.mk

pkgs/development/beam-modules/fetch-hex.nix

@@ -0,0 +1,34 @@
+{ stdenv, fetchurl }:
+
+{ pkg, version, sha256
+, meta ? {}
+}:
+
+with stdenv.lib;
+
+stdenv.mkDerivation ({
+  name = "hex-source-${pkg}-${version}";
+
+  src = fetchurl {
+    url = "https://s3.amazonaws.com/s3.hex.pm/tarballs/${pkg}-${version}.tar";
+    inherit sha256;
+  };
+
+  phases = [ "unpackPhase" "installPhase" ];
+
+  unpackCmd = ''
+    tar -xf $curSrc contents.tar.gz
+    mkdir contents
+    tar -C contents -xzf contents.tar.gz
+  '';
+
+  installPhase = ''
+    runHook preInstall
+    mkdir "$out"
+    cp -Hrt "$out" .
+    success=1
+    runHook postInstall
+  '';
+
+  inherit meta;
+})