title: Can I insert into a map by key in F#?
body: <p>I'm messing around a bit with F# and I'm not quite sure if I'm doing this correctly. In C# this could be done with an IDictionary or something similar.</p>
  
  <pre><code>type School() =
     member val Roster = Map.empty with get, set
  
     member this.add(grade: int, studentName: string) =
        match this.Roster.ContainsKey(grade) with
          | true -&gt; // Can I do something like this.Roster.[grade].Insert([studentName])?
          | false -&gt; this.Roster &lt;- this.Roster.Add(grade, [studentName])
  </code></pre>
  
  <p>Is there a way to insert into the map if it contains a specified key or am I just using the wrong collection in this case?</p>