code: function passthru_prelude(tokenOrForm) {
    // the expression returned is a "no-op" represented as (nop)
    // it's only purpose is to have something for the prelude to hang on
    // (note we scrub "(nop)" from the pretty-printed parse trees btw)
    var nop = sl.list("nop");
    if(tokenOrForm && tokenOrForm.prelude) {
      nop.prelude = tokenOrForm.prelude;
    }
    return nop;
  }
docs: Read functions that just have side effects (e.g. "#use")
  can return "reader.passthru_prelude" to pass comments or
  whitespace that preceded the directive.