Persistent values from the first line

Why the canonical post model is a record, and why collections are persistent rather than mutable.

The canonical model is an immutable value. Posts are records, collections are persistent Vectors and Maps, and no build step mutates a value in place.

Records for domain values

A canonical post has a fixed field set, so the model declares it once:

(defrecord Post
  [id slug title summary body published-at updated-at authors tags cover draft
   pinned-weight provenance aliases comment-channels])

Reading a field is direct keyword lookup, and the type has an exact predicate. Cross-source identity is the id field, never a title or a derived path.

Persistent collections

Lists, vectors, maps, and sets share structure instead of copying. The builder folds over a vector to accumulate documents, which is ordinary Lisp-style code:

• Collection/get reads a key with a fallback,
• Collection/assoc returns a new map,
• Collection/conj returns a new vector,
• Order/sort returns a new vector without mutating its input.

That last property is what makes the build deterministic. Sorting cannot observe or disturb the module-level constants it consumes.

Why this matters for a blog

A build is a pure function from normalized input to output. When the input and the renderer identity are equal, the output bytes are equal too. Determinism is a property of the value model, not a promise layered on top of it.

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