Updating nested immutable data structures

Question

I want to update a nested, immutable data structure (I attached a small example of a hypothetical game.) And I wonder whether this can be done a little more elegantly.

Answer 1

I asked a similar question, but about haskell: Is there a Haskell idiom for updating a nested data structure?

The excellent answers mentioned a concept known as functional lenses.

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Unfortunately, I don't know what the package is, or if it even exists, for F#.

Update: two knowledgeable F#-ists (F#-ers? F#as?) left useful links about this in comments, so I'll post them here:

• @TomasPetricek suggested FSharpX and this website describing it

• @RyanRiley gave the link for the package

It's awesome that these two guys took the time to read my answer, comment and improve it, as they're both developers of FSharpX!

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More extraneous information: I was motivated to figure out how to do this by Clojure's assoc-in and update-in functions, which proved to me that it is possible in functional languages! Of course, Clojure's dynamic typing makes it simpler than in Haskell/F#. Haskell's solution involves templating, I believe.