A Logos atom (mutable-reference-via-process): %Logos.Atom{pid: pid()}. This is unrelated to Elixir's :atom type (an interned symbolic constant) -- a Logos atom is a mutable reference cell, analogous to Clojure's atom.

This Elixir struct is deliberately just an identity wrapper -- an address, exactly like Logos.Pid -- around the pid of a small self-recursive Lisp loop process (atom-loop in concurrency.logos) that actually holds and services the atom's state. No stateful behaviour lives here: atom/deref/swap!/reset! are ordinary Lisp functions in concurrency.logos, built on spawn/send/receive (the Logos.Process primitives). This is intentionally not an Elixir GenServer/Agent reimplementation: keeping the atom's state machine as plain message-passing Lisp code (rather than special-cased Elixir behaviour) keeps the Elixir-level primitive surface small and lets atoms be inspected/reasoned about like any other Logos value. See concurrency.logos's "atoms" section for the loop process itself.

Kept as a distinct struct from Logos.Pid (rather than reusing Logos.Pid directly) so that Logos-level predicates like a hypothetical atom?/pid? can tell the two apart, and so deref/swap!/reset!'s Elixir-level primitive clauses (Logos.Primitives) can pattern-match on %Logos.Atom{} specifically -- atom and pid are two separate runtime value cases and must never be conflated even though an atom is, underneath, just a pid wrapped one layer deeper.