await [sequencing](https://alexn.org/blog/2017/01/30/asynchronous-programming-scala.html#h4-1)

CSharpVsScalaAsync

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Imaging;
using System.Windows.Navigation;
using System.Windows.Shapes;

namespace ScalaAsync
{
    /// <summary>
    /// Interaction logic for MainWindow.xaml
    /// </summary>
    public partial class MainWindow : Window
    {
        public MainWindow()
        {
            InitializeComponent();
        }

        private async void button_Click(object sender, RoutedEventArgs e)
        {
            int res = await sumAsync(ReadTexts());
            textBox0.Text = res.ToString();
        }

        async Task<int> ReadText1()
        {
            await Task.Delay(1000);
            int res;
            if (int.TryParse(textBox1.Text, out res))
            {
                return res;
            } else
            {
                return -1000;
            }
        }
        async Task<int> ReadText2()
        {
            await Task.Delay(2000);
            int res;
            if (int.TryParse(textBox2.Text, out res))
            {
                return res;
            }
            else
            {
                return -2000;
            }
        }
        async Task<int> ReadText3()
        {
            await Task.Delay(3000);
            int res;
            if (int.TryParse(textBox3.Text, out res))
            {
                return res;
            }
            else
            {
                return -3000;
            }
        }

        List<Task<int>> ReadTexts()
        {
            return new List<Task<int>>()
            {
                ReadText1(),
                ReadText2(),
                ReadText3()
            };
        }

        private async Task<int> sumAsync(List<Task<int>> list)
        {
            int sum = 0;
            foreach (var f in list)
            {
                sum += await f;
            }
            return sum;
        }
    }
}

Second example with explicit closure

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Imaging;
using System.Windows.Navigation;
using System.Windows.Shapes;

namespace ScalaAsync
{
    /// <summary>
    /// Interaction logic for MainWindow.xaml
    /// </summary>
    public partial class MainWindow : Window
    {
        public MainWindow()
        {
            InitializeComponent();
        }

        private void button_Click(object sender, RoutedEventArgs e)
        {
            var action = sumAsync(ReadTexts());
            action();
        }

        async Task<int> ReadText1()
        {
            await Task.Delay(1000);
            int res;
            if (int.TryParse(textBox1.Text, out res))
            {
                return res;
            } else
            {
                return -1000;
            }
        }
        async Task<int> ReadText2()
        {
            await Task.Delay(2000);
            int res;
            if (int.TryParse(textBox2.Text, out res))
            {
                return res;
            }
            else
            {
                return -2000;
            }
        }
        async Task<int> ReadText3()
        {
            await Task.Delay(3000);
            int res;
            if (int.TryParse(textBox3.Text, out res))
            {
                return res;
            }
            else
            {
                return -3000;
            }
        }

        List<Task<int>> ReadTexts()
        {
            return new List<Task<int>>()
            {
                ReadText1(),
                ReadText2(),
                ReadText3()
            };
        }

        private Action sumAsync(List<Task<int>> list)
        {
            int sum = 0;
            return async delegate
            {
                foreach (var f in list)
                {
                    sum += await f;
                }
                textBox0.Text = sum.ToString();
            };
        }
        //more about closures and anonymous methods in C# https://stackoverflow.com/a/428624
    }
}