// VarContext is thread-safe AFTER the first variable has been defined

// or after you call makeThreadSafe(), whichever comes first

sclass VarContext {

  gettable VarContext parent;

  MapSO vars;

  *() {}

  *(VarContext *parent) {}

  O get(S name) {

    if (containsKey(vars, name))

      ret mapGet(vars, name);

    if (parent != null)

      ret parent.get(name);

    null;

  }

  void set aka put(S name, O value) {

    vars = putOrCreateSyncMap(vars, name, value);

  }

  AutoCloseable tempSet aka tempPut(S name, O value) {

    initMap();

    ret main tempPut(vars, name, value);

  }

  void unset(S name) {

    remove(vars, name);

  }

  void printMe {

    pnl(vars);

    print(+parent);

  }

  void makeThreadSafe aka initMap() {

    vars if null = syncHashMap();

  }

  // mechanism for returning from a script

  settable O exitFromScript;

  settable O returnValue;

  bool exiting() { ping(); ret exitFromScript != null; }

}