title: How to use setIn with immutable.js List
body: <p>Ok I've got a list of objects, pretty standard.</p>
  
  <p><code>const list = Immutable.List([{type:'thang',data:{id:'pants'}}]);</code></p>
  
  <p>Now I want to change pants to shorts... so I'm thinking </p>
  
  <p><code>list.setIn([0,'data','id'],'shorts');</code></p>
  
  <p>Alas</p>
  
  <p><code>Error: invalid keyPath</code></p>
  
  <p>How is this done? </p>
  
  <p>I can't even get this far despite messing around with this for a while :/ Once I know how to do this I'd like to know how to add a new element at a position</p>
  
  <p><code>list.setIn([0,'data','length'],'short');</code></p>
  
  <p>To add a new length attribute to the data object at position 0 in the list.</p>