static LPair<S, Map> allMapCacheVars() {
  ret allMapCacheVars(mc());
}

static LPair<S, Map> allMapCacheVars(O mc) {
  new LPair<S, Map> l;
  for (S var : allCacheVars(mc)) {
    O o = get(mc, var);
    if (o cast Map)
      l.add(pair(var, o));
  }
  ret l;
}

Began life as a copy of #1015976