title: "Block following this 'let' is unfinished" error f#
body: <p>I'm trying to write a string list to a file using WriteAllLines from the .Net library.
  I'm getting an error on the last line</p>
  
  <p>"Block following this let is unfinished. Expect an expression."
  I'm looking at this for an hour now, cant find anything out. Can someone help?</p>
  
  <pre><code>let rec ConvertToString list =
     match list with
     | [l] -&gt; l.ToString()
     | head :: tail -&gt; head.ToString() + ConvertToString tail
     | [] -&gt; ""
  
  
  let rec WriteImage(filepath:string, width:int, height:int, depth:int, image:int list list) = 
    if image = [] then 
     System.IO.File.WriteAllLines(filepath, L)
     true  // success
    else 
     let L = ConvertToString(image.Head) :: WriteImage(filepath, width, height, depth, image.Tail)
  </code></pre>