anchor.diff:  , buildPhase ? null
   , configurePhase ? null
   , meta ? {}
  -, enableDebugInfo ? false
   , ... }@attrs:
   
   with lib;
  
positive.code:     (_: v: v != null)
      { inherit setupHook configurePhase buildPhase installPhase; };
  
    pkg = self: stdenv.mkDerivation (attrs // {
  
      name = "${name}-${version}";
      inherit version;
  
      buildInputs = buildInputs ++ [ erlang rebar3 openssl ];
      propagatedBuildInputs = [checkouts];
  
      dontStrip = true;
  
      inherit src;
  
      setupHook = writeText "setupHook.sh" ''
         addToSearchPath ERL_LIBS "$1/lib/erlang/lib/"
      '';
  
      configurePhase = ''
        runHook preConfigure
        ${if checkouts != null then
            "cp --no-preserve=all -R ${checkouts}/_checkouts ."
          else
            ""}
        runHook postConfigure
      '';
  
  
negative.code: { stdenv, erlang, rebar3WithPlugins, openssl,
    lib }:
  
  { name, version
  , src
  , beamDeps ? []
  , buildPlugins ? []
  , checkouts ? null
  , releaseType
  , buildInputs ? []
  