diff --git a/README.md b/README.md
--- a/README.md
+++ b/README.md
@@ -9,7 +9,7 @@
 It consists of multiple commands:
 - `elm2nix convert`: Given `elm.json` in current directory, all dependencies are
   parsed and their sha256sum calculated
-- `elm2nix snapshot`: Downloads snapshot of http://package.elm-lang.org into `versions.dat`
+- `elm2nix snapshot`: Downloads snapshot of https://package.elm-lang.org/all-packages json and converts into binary `registry.dat` used by [elm-compiler](https://github.com/elm/compiler/blob/047d5026fe6547c842db65f7196fed3f0b4743ee/builder/src/Stuff.hs#L147) as a cache
 - `elm2nix init`: Generates `default.nix` that glues everything together
 
 ## Assumptions
@@ -36,7 +36,8 @@
     $ cd elm-todomvc
     $ elm2nix init > default.nix
     $ elm2nix convert > elm-srcs.nix
-    $ elm2nix snapshot > versions.dat
+    # generates ./registry.dat
+    $ elm2nix snapshot
     $ nix-build
     $ chromium ./result/Main.html
 
@@ -50,22 +51,24 @@
 
 As it's considered experimental, it's generated for now. Might change in the future.
 
-### How to use with ParcelJS and Yarn?
+### How do I use elm2nix with [ParcelJS][parceljs] and [Yarn][yarn-v1]?
 
-Instead of running `elm2nix init`, use something like:
+Instead of running `elm2nix init`, create a `default.nix` with the following derivation:
 
 ```nix
 { pkgs ? import <nixpkgs> {}
 }:
 
 let
-  yarnPkg = pkgs.yarn2nix.mkYarnPackage {
+  yarnPkg = pkgs.mkYarnPackage {
     name = "myproject-node-packages";
-    packageJSON = ./package.json;
-    unpackPhase = ":";
-    src = null;
+    src = pkgs.lib.cleanSourceWith {
+      src = ./.;
+      name = "myproject-node-packages.json";
+      filter = name: type: baseNameOf (toString name) == "package.json";
+    };
     yarnLock = ./yarn.lock;
-    publishBinsFor = ["parcel-bundler"];
+    publishBinsFor = ["parcel"];
   };
 in pkgs.stdenv.mkDerivation {
   name = "myproject-frontend";
@@ -89,12 +92,16 @@
 
   configurePhase = pkgs.elmPackages.fetchElmDeps {
     elmPackages = import ./elm-srcs.nix;
-    versionsDat = ./versions.dat;
+    elmVersion = "0.19.1";
+    registryDat = ./registry.dat;
   };
 
   installPhase = ''
     mkdir -p $out
-    parcel build -d $out index.html
+    parcel build --dist-dir $out index.html
   '';
 }
 ```
+
+[parceljs]: https://parceljs.org/
+[yarn-v1]: https://classic.yarnpkg.com/lang/en/
diff --git a/elm2nix.cabal b/elm2nix.cabal
--- a/elm2nix.cabal
+++ b/elm2nix.cabal
@@ -3,7 +3,7 @@
 -- see: https://github.com/sol/hpack
 
 name:           elm2nix
-version: 0.3.0
+version: 0.3.1
 synopsis:       Turn your Elm project into buildable Nix project
 description:    Please see the README on Github at <https://github.com/domenkozar/elm2nix#readme>
 homepage:       https://github.com/domenkozar/elm2nix#readme
diff --git a/src/Elm2Nix.hs b/src/Elm2Nix.hs
--- a/src/Elm2Nix.hs
+++ b/src/Elm2Nix.hs
@@ -11,7 +11,7 @@
 
 import Control.Concurrent.Async (mapConcurrently)
 import Control.Monad (liftM2)
-import Control.Monad.Except (liftIO, MonadIO)
+import Control.Monad.IO.Class (liftIO, MonadIO)
 import Control.Monad.Trans.Except (ExceptT, runExceptT, throwE)
 import Data.Aeson (Value(..))
 import Data.List (intercalate, nub)