using uCalcSoftware;

var uc = new uCalc();

static void MySum(uCalc.Callback cb) {
   var Total = 0.0;
   var Expr = cb.ArgExpr(1);
   var Start = cb.Arg(2);
   var Finish = cb.Arg(3);
   var Variable = cb.ArgItem(4);

   for (double x = Start; x <= Finish; x++) {
      Variable.Value(x);
      Total += Expr.Evaluate();
   }
   cb.Return(Total);
}

uc.DefineVariable("x");
uc.DefineFunction("Sum(ByExpr Expr, Start, Finish, ByHandle Var)", MySum);
Console.WriteLine(uc.Eval("Sum(x ^ 2, 1, 10, x)"));