[runT1ME]

It's awkward to work with fully nested structures. Think about having a map of customer objects which have a list of addresses and you need to update everyone's first address to be capitalized for some raeson. You'd really want a fully fleshed out lens library and maybe even macros for auto generating them on your concrete data structures to make it easy to 'update' (via a persistent structure) without having to deal with all the cruft of doing it by hand.

[pmapcat]

That is the use case that we have to work with quite often. In the end, we use something along the lines of

  (update-fn (fn [{:keys [address]}
                   :as customer]
               (if address (update customer :address clojure.string/capitalize) customer))
    customers)

which pattern matches on some `object` (map) and does processing. We find it less fragile than specifying explicit path to an element. It can also work in a polymorphic fashion. On the other hand, there is a risk of a false positive (when you modify address that you shouldn't). But you can mitigate that risk by using additional checks (in case of a customer, you can check for additional set of fields that are specific for that object(map) edit:formatting

[simongray]

I agree that you want specialised mini-DSLs for querying and updating highly nested structures (... which you should probably avoid creating anyway), but for such a simple task you could just do this (Clojure example):

    (update-vals customers #(update-in % [:address 0] str/capitalize))

[mlajtos]

In JavaScript world, there is ImmutableJS, which uses this style of updates. However, there is better approach which is what ImmerJS uses – you write a function where you can do mutation to the target data structure, wrap it in a "produce" function, and library will pick on those mutations and create a new copy of the data that is structurally shared with the original.

https://immerjs.github.io/immer/