Comment by matheusmoreira

> note! repl implies there's a top-level but there isn't...

I'm a little confused. How could it not have a top-level environment? There are environments which are extended on function application by consing lists of variables and their values onto the old environment.

  void* extend(void* env, void* vars, void* vals) {
    return cons(cons(vars, vals), env);
  }

This implies a root environment whose cdr is nil.