// 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; }
}

Began life as a copy of #1033977