First values

You want a small vector and a map, their sizes, and a stable identity — without a file or a server. Build them as Dacite values. Count, get, and the content hash are the whole API you need here.

Five minutes. nbb only; no JVM.

Prerequisites

• Node.js 18+
• A clone of the dacite repository

git clone https://github.com/jclaggett/dacite.git
cd dacite
npm install

Run the example

npm run hello

Expected shape of the output:

Dacite Hello World
  vector count : 3
  vector hash  : 58a4799b…
  map count    : 2
  map hash     : 5de2bb0c…
  (get m "hello") realized: 42
Done.

The exact hashes are stable across hosts (JVM, babashka, nbb) for the same value structure — that is part of the Dacite porting contract.

What the code does

Source: hello.cljc.

1. Create a mem store — an in-memory rooted store.

   (def st (store/mem))
   

2. Build values — first argument is always a store, root, or peer value:

   (def v (v/vector st 1 2 3))
   (def m (v/map v
                 "hello" (v/i64 v 42)
                 "vec" v))
   

3. Read with dacite.value — collection ops take the value first:

   (v/count v)              ; => 3
   (v/get m "hello")        ; => Dacite scalar
   (v/realize …)            ; => 42
   

4. Content hash — identity is the hash, independent of store location:

   (store/hash->hex (v/hash v))
   

Try it in a one-liner

npx nbb -e "
(require '[dacite.store :as store]
         '[dacite.value :as v])
(let [st (store/mem)
      vec (v/vector st 1 2 3)]
  (println (v/count vec))
  (println (store/hash->hex (v/hash vec))))
"

Next steps

• Anatomy of a Dacite app — add a root and persist
• Persist and update a document — nested map, file or HTTP
• Values API — constructors, collection ops