using uCalcSoftware;

var uc = new uCalc();

static void DoublePositive(uCalc.Callback cb) {
   // If input is negative, raise a syntax error.
   if (cb.Arg(1) < 0) {
      cb.Error.Raise(ErrorCode.Syntax_Error);
   }
   cb.Return(cb.Arg(1) * 2);
}

uc.DefineFunction("DoublePositive(x)", DoublePositive);
Console.WriteLine(uc.EvalStr("DoublePositive(10)"));
Console.WriteLine(uc.EvalStr("DoublePositive(-5)"));