Hi all, I'm slowly shopping around for a functional language. The first one I seriously considered was Clojure, because of its agents; but I'm now realizing that most of my concurrency needs can be met using 'par' and 'seq', so I'm thinking about giving Haskell a closer look. However, Clojure's collections (maps, lists, vectors, sets) have a couple of features that I would really miss: - Cheap 'manipulation'. In the following: user=> (def m {:a 1 :b 2}) #'user/m1 user=> (assoc m :a 3) {:a 3, :b 2} the 'assoc' function produces a new map which actually shares structure with m, meaning it doesn't need to make a full copy in memory; but it also leaves m unchanged. This works efficiently even for nested, mixed collections. - Cheap equality by value: user=> (= m {:a 1 :b 2 :c {:d 3 :f 4}}) false user=> (= m {:a 1 :b 2}) true If I understand correctly, equality is computed based on some kind of hash rather than by comparing the two maps element by element, so it's efficient even for large and/or nested collections. Do Haskell's data structures have analogous properties? If not, are there libraries providing such data structures? Thanks, Anand