Program.cs

await foreach (string line in ReadLinesAsync(args[0]))
{
    Console.WriteLine(line);
}

static async IAsyncEnumerable<string> ReadLinesAsync(string path)
{
    using (var bodyTextReader = new StreamReader(path))
    {
        while (!bodyTextReader.EndOfStream)
        {
            string? line = await bodyTextReader.ReadLineAsync();
            if (line is not null) { yield return line; }
        }
    }
}



// These examples illustrate features that are built into .NET. We don't
// want to define it ourselves, hence the #if false
#if false
bool MoveNext();


public interface IAsyncEnumerable<out T>
{
    IAsyncEnumerator<T> GetAsyncEnumerator(
        CancellationToken cancellationToken = default);
}

public interface IAsyncEnumerator<out T> : IAsyncDisposable
{
    T Current { get; }

    ValueTask<bool> MoveNextAsync();
}
#endif