sclass OpsOnVars {

  MapSO vars = syncTreeMap();

  sclass NotRunYet {}

  static new NotRunYet notRunYet;

  *(O... _) {

    addParamsToMap_inPlace(vars, _);

  }

  O getVar aka get(S var) { ret vars.get(var); }

  void setVar aka set(S var, O value) { if (var != null) vars.put(var, value); }

  record SetVar(S var, O value) is Runnable {

    run { setVar(var, value); }

  }

  // SINGLE-OPS (one input variable, one output variable)

  macro singleOpCtors {  

    *() {}

    *(S *inVar, S *outVar) {}

  }

  abstract noeq record SingleOp(S inVar, S outVar) is Runnable {

    transient O value = notRunYet;

    abstract O perform(O arg);

    run { get(); }

    O get() {

      value = perform(getVar(inVar));

      setVar(outVar, value);

      ret value;

    }

  }

  // MULTI-OPS (multiple input variables, one output variable)

  abstract noeq record MultiOp(LS inVars, S outVar) is Runnable {

    transient O value = notRunYet;

    abstract O perform(L values);

    *(S... vars) {

      outVar = last(vars);

      inVars = asListMinusLast(vars);

    }

    run { get(); }

    O get() {

      value = perform(map getVar(inVars);

      setVar(outVar, value);

      ret value;

    }

  }

  macro multiOpCtors {  

    *() {}

    *(LS *inVars, S *outVar) {}

    *(S... vars) { super(vars); }

  }

}