Lavash.Component.Calculate (Lavash v0.3.0-rc.2)

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A calculated field computed from state using a reactive expression.

Calculations use rx() to capture expressions that reference state via @field syntax. By default, they are transpiled to JavaScript for client-side optimistic updates.

Fields

  • :name - The atom name of the calculated field
  • :rx - A Lavash.Rx struct containing the expression
  • :optimistic - Whether to transpile to JS (default: true, auto-set to false if not transpilable)
  • :async - Whether to compute asynchronously (default: false)
  • :reads - Ash resources to watch for PubSub invalidation (default: [])

Usage

# Simple reactive calculation - transpiles to JS
calculate :tag_count, rx(length(@tags))
calculate :can_add, rx(@max == nil or length(@items) < @max)

# Server-only (explicit or auto-detected)
calculate :server_only, rx(complex_fn(@data)), optimistic: false

# Async calculation - returns AsyncResult (loading/ok/error)
calculate :factorial, rx(compute_factorial(@n)), async: true

# With resource invalidation
calculate :product_count, rx(length(@products)), reads: [Product]