The System.IO is not permit in algorithm why ?

The sample in Rest Api use the System.IO.MemoryStream

///

/// When we have a new event trigger, buy some stock:

///

public List GenerateFromURL(string url)

{

List events = new List();

byte[] rawData = null;

string line;

using (var wc = new System.Net.WebClient())

rawData = wc.DownloadData(url);

MemoryStream stream = new MemoryStream(rawData);

using (StreamReader sr = new StreamReader(stream))

{

sr.ReadLine();

while ((line = sr.ReadLine()) != null)

{

Weather w = new Weather(line);

events.Add(w);

if (w.errString != "")

Debug("Weather Err:" + w.errString);

}

}

return events;

}

How to find a solution ?