Skuld.Effects.EventAccumulator (skuld v0.1.26)

View Source

Effect for accumulating events during computation.

Accumulates events in a simple list, preserving emission order. This follows the Decider pattern where Events are facts about what happened.

Example

alias Skuld.Effects.{EventAccumulator, ChangeEvent}
alias Skuld.Comp

use Skuld.Syntax

# Accumulate events during computation
comp do
  user_cs = User.changeset(%User{}, %{name: "Alice"})
  _ <- EventAccumulator.emit(ChangeEvent.insert(user_cs))

  order_cs = Order.changeset(%Order{}, %{user_id: 1})
  _ <- EventAccumulator.emit(ChangeEvent.insert(order_cs))

  return(:ok)
end
|> EventAccumulator.with_handler(output: &{&1, &2})
|> Comp.run!()
#=> {:ok, [%ChangeEvent{...}, %ChangeEvent{...}]}

Options

The with_handler/2 accepts:

  • :output - Transform function (result, events) -> output. Default returns just the result, discarding the events. Use output: &{&1, &2} to get {result, events}.

Grouping Events

If you need to group events by type, use EventAccumulator.IEvent.tag/1:

{result, events} = ...
events_by_tag = Enum.group_by(events, &EventAccumulator.IEvent.tag/1)

See Also

Summary

Functions

__handle__(comp, opts)

Install EventAccumulator handler via catch clause syntax.

emit(event)

Emit an event.

with_handler(comp, opts \\ [])

Install handler to capture events.

Functions

__handle__(comp, opts)

Install EventAccumulator handler via catch clause syntax.

Config is opts (or nil for defaults):

catch
  EventAccumulator -> nil
  EventAccumulator -> [output: fn r, events -> {r, events} end]

emit(event)

@spec emit(term()) :: Skuld.Comp.Types.computation()

Emit an event.

The event will be accumulated in emission order.

Returns :ok.

Example

_ <- EventAccumulator.emit(ChangeEvent.insert(changeset))
_ <- EventAccumulator.emit(%MyCustomEvent{data: "hello"})

with_handler(comp, opts \\ [])

@spec with_handler(
  Skuld.Comp.Types.computation(),
  keyword()
) :: Skuld.Comp.Types.computation()

Install handler to capture events.

Options

  • :output - Transform function (result, events) -> output. Default returns just the result, discarding the events. Use output: &{&1, &2} to get {result, events}.

Example

comp
|> EventAccumulator.with_handler()
|> Comp.run!()
#=> result (events discarded)

comp
|> EventAccumulator.with_handler(output: &{&1, &2})
|> Comp.run!()
#=> {result, [event1, event2, ...]}

comp
|> EventAccumulator.with_handler(output: fn _result, events -> events end)
|> Comp.run!()
#=> [event1, event2, ...]