Commit loops

The store’s mutable cell is a hash. Wrap it once:

(def r (v/root rs))
(def books (v/root (s/lens rs (v/vector rs "books"))))  ; same ops, nested path

(or (v/deref r)
    (let [seed (v/map r "theme" "dark")]
      (v/cas! r nil seed)
      seed))

swap! is read → apply f → CAS. If another writer landed first, f runs again on the new current value. Domain functions must be retries-safe: compute the next value from the argument, do not close over a stale copy.

(v/swap! r add-todo "milk")
;; add-todo is (fn [todos title] (v/conj todos …))

A lens (s/lens rs path) is a rooted store whose root / cas! / swap! talk about the nested value. path is a Dacite vector of keys (or a host seq). The document cell is unchanged. This is client convenience, not an HTTP path. See Rooted stores — lenses.

See Two writers, one CAS.