Full Example & Setup

var output = result.Value switch
{
    Success<Todo> s  => $"OK: {s.Data.Title}",
    HttpError h      => $"HTTP {h.StatusCode}: {h.Message}",
    TransportError t => $"Transport error: {t.Exception.Message}",
    _                => "Unknown"
};

var result = await httpClient.GetJsonAsync<Todo>("https://api.example.com/todos/1");

var summary = await result
    .MapAsync(async todo => todo with { Title = todo.Title.ToUpperInvariant() })
    .ContinueWith(t => t.Result.Bind(todo =>
        todo.Completed
            ? ApiResult.Ok($"Done: {todo.Title}")
            : ApiResult.HttpFail<string>(HttpStatusCode.UnprocessableEntity, "Not completed")));

Console.WriteLine(summary.Value switch
{
    Success<string> s => s.Data,
    HttpError h       => $"Error {h.StatusCode}: {h.Message}",
    TransportError t  => $"Transport: {t.Exception.Message}",
    _                 => "?"
});

var result = await httpClient.GetJsonAsync<Todo>(url);