run esy under NixOS

esy.nix

{ pkgs ? import <nixpkgs> {} }:                                                                                               
                                                                                                                              
(pkgs.buildFHSUserEnv {                                                                                                       
  name = "esy-env";
  targetPkgs = pkgs: (with pkgs;                                                                                              
    [                                                                                                                         
      # this set suffices to build esy 0.3.4 with esy 0.2.11
      # and also to build the hello-ocaml demo with esy 0.3.4
      nodejs-10_x
      stdenv.cc
      stdenv.cc.bintools
      gnumake
      which
      m4
      perl
      patch
      # this is for an optional feature
      libbfd
    ]);
  multiPkgs = pkgs: ([]);
  runScript = "bash";
}).env