title: Is the whole Map copied when a new binding is inserted?
body: <p>I would like to better understand the interns of e.g. Data.Map. When I insert a new binding in a Map, then, because of immutability of data I get back a new data structure that is identical with the old data structure plus the new binding.</p>
  
  <p>I would like to understand how this is achieved. Does the compiler eventually implement this by copying the whole data structure with e.g. millions of bindings? Can it generally be said that mutable data structures/arrays (e.g. Data.Judy) or imperative programming languages perform better in such cases? Does immutable data have any advantage when it comes to dictionaries/key-value stores?</p>