{ lib, buildEnv, yarn, overmind, ruby_2_5, nodejs-10_x ? null }:

let
 pkgsNewEnough = (lib.versionAtLeast yarn.version "1.10.0") && (nodejs-10_x != null);

 webpkgs = if pkgsNewEnough
   then { inherit yarn nodejs-10_x; }
   else builtins.trace "Using <nixpkgs-unstable> channel for web packages"
        (import <nixpkgs-unstable> {});
in

let
 nodejs = webpkgs.nodejs-10_x;
 yarn   = webpkgs.yarn.override { inherit nodejs; };
in

buildEnv {
 name = "eikaiwa-packages";
 paths = [
   nodejs
   yarn
   overmind
   ruby_2_5
 ];
}