title: What is the benefit of purely functional data structure?
body: <p>There are large number of texts on data structures, and libraries of data structures code. I understand that purely functional data structure is easier to reason about. However I have trouble to understand the real world advantage of using purely functional data structure in pragmatic code (using functional programming language or not) over the imperative counterpart. Can somebody provide some real world cases where purely functional data structure has advantage and why?</p>
  
  <p>Examples along the line like I use <strong>data_structure_name</strong> in <strong>programming_language</strong> to do <strong>application</strong> because it can do <strong>certain_thing</strong>. </p>
  
  <p>Thanks.</p>
  
  <p>PS: What I mean by purely functional data structure is not the same as persistent data structure. Persistent data structure is a data structure that doesn't change?? On other hand purely functional data structure is a data structure that operates purely.</p>