Function read

repos/effect/packages/effect/src/unstable/reactivity/Atom.ts:1180–1208

(
    get: AtomContext,
    services?: Context.Context<any>
  )

  const [read, write] = makeResultFn(f, options)
  return writable(read, write) as any
}

function makeResultFn<Arg, E, A>(
  f: (arg: Arg, get: FnContext) => Effect.Effect<A, E, Scope.Scope | AtomRegistry> | Stream.Stream<A, E, AtomRegistry>,
  options?: {
    readonly initialValue?: A
    readonly concurrent?: boolean | undefined
  }
) {
  const argAtom = removeTtl(state<[number, Arg | Interrupt]>([0, undefined as any]))
  const initialValue = options?.initialValue !== undefined
    ? AsyncResult.success<A, E>(options.initialValue)
    : AsyncResult.initial<A, E>()
  const fibersAtom = options?.concurrent
    ? removeTtl(readable((get) => {
      const fibers = new Set<Fiber.Fiber<any, any>>()
      get.addFinalizer(() => fibers.forEach((f) => f.interruptUnsafe()))
      return fibers
    }))
    : undefined

  function read(
    get: AtomContext,
    services?: Context.Context<any>
  ): AsyncResult.AsyncResult<A, E | Cause.NoSuchElementError> {
    const fibers = fibersAtom ? get(fibersAtom) : undefined
    ;(get as any).isFn = true
    const [counter, arg] = get.get(argAtom)
    if (counter === 0) {
      return initialValue
    } else if (arg === Interrupt) {
      return AsyncResult.failureWithPrevious(Cause.interrupt(), { previous: get.self() })