In c#, how to yield until a download is complete?

Ok, I'm trying retreive data from a php file that access a database. That works fine. At the moment I'm using a javascript file to access the php file, which also works fine.

But I want to use a c# version as I've got custom c# classes that will mold the data.

The one thing I've not been able to convert to c# is the yield part below:

 // Post the URL to the site and create a download object to get the result.
   hs_get = WWW(check_url);

   yield hs_get; // Wait until the download is done

I understand that i need to use coroutines. However all the examples use a prespecified time. Where as the javascript above doesn't use any as it waits until the transfer/download is complete. what would be an equilvalent in c#?

Use `yield return WWW` to wait for completion

void Download () {
     //In C#, you have to explicitly start a corotine.

IEnumerator FinishDownload (string url) {
     WWW hs_get = new WWW(url);

    yield return hs_get;

    //Work with the retrieved info.