Lavash.Actions.PreRun (Lavash v0.4.0-rc.4)

Copy Markdown View Source

Pre-cascade imperative escape hatch for actions.

Runs BEFORE the reactive cascade. Takes a socket, returns a socket. The user is responsible for writing state via Lavash.Socket.put_state/3 (or any LV-style write that updates socket.assigns.__changed__) — the action runtime extracts __changed__ after the body to populate lavash's dirty set, so the cascade sees what changed and recomputes precisely.

When to use

pre_run fn socket ->
  # Validate / preprocess BEFORE state mutates
  if socket.assigns.form_valid? do
    Lavash.Socket.put_state(socket, :submitted, true)
  else
    raise "validation failed"  # or just return socket unchanged
  end
end

Use pre_run when you need imperative Elixir to compute a state value that downstream calcs depend on. The cascade fires after, and your write is visible to it.

For state mutation that fits rx(), prefer the declarative set :foo, rx(...). For socket-level ops that don't write state (push_event, stream_insert, etc.) and that want to observe POST-cascade state, use run (the post-cascade socket op).

Fields

  • :fun — quoted AST of the fn socket -> socket end body. Compiled at runtime into a __lavash_pre_run__/3 clause on the user's module, same pattern as Run/SocketRun.