public async Task <double> VisitAsync(BinaryExpression node)
{
char operation;
switch (node.NodeType)
{
case ExpressionType.Add:
{
operation = '+';
break;
}
case ExpressionType.Subtract:
{
operation = '-';
break;
}
case ExpressionType.Multiply:
{
operation = '*';
break;
}
case ExpressionType.Divide:
{
operation = '/';
break;
}
default:
{
throw new ArgumentException();
}
}
var before = new[]
{
new Lazy <Task <double> >(VisitAsync((dynamic)node.Left)),
new Lazy <Task <double> >(VisitAsync((dynamic)node.Right))
};
var numbers = await Task.WhenAll(before.Select(x => x.Value));
var result = await _calculator.CalculateAsync(numbers[0], operation, numbers[1]);
Console.WriteLine(node);
return(result);
}