# `Statifier.Effect.Trace.ExitSet`
[🔗](https://github.com/riddler/statifier-ex/blob/v2.0.0/lib/statifier/effect/trace/exit_set.ex#L1)

Trace payload for `{:trace, %__MODULE__{}}` - emitted before any state is
exited (`docs/observability.md` constraint 2's "exit set" row). `indexes`
are the states to be exited (constraint 3, integer indexes), in exit
order.

Two sites emit it, matching the two places this engine exits states:
`Statifier.Interpreter.ExitEntry.exit_states/2` over `compute_exit_set`'s
result, and `Statifier.Interpreter.exit_interpreter/1` over the whole
configuration at termination. Both are phase boundaries Appendix D names
(`exitStates` and `exitInterpreter` compute the same `statesToExit`), so
ADR-0012 item 2 asks for the row at both.

`configuration` is the full configuration (ADR-0005, ancestors included)
as it stands *after* every state in `indexes` has left it, so a consumer
can render the configuration per microstep without folding deltas. It is
deliberately the only field taken from the post-exit
state; `macrostep`/`microstep`/`round` are stamped from the state as it
stood at the phase boundary the payload names, which is what keeps this
payload an "exit set" marker rather than an after-the-fact report
(`test/fixtures/adr_judge/0012_trace_prestate_captured.diff` is the
sanctioned shape). At `Statifier.Interpreter.exit_interpreter/1` the sweep
empties the configuration, so `configuration` is `MapSet.new()` there -
which is the true resulting configuration and not a missing value;
`Trace.Done.configuration`, which carries the configuration as it stood
*at* exit, is the payload that answers "what was active when the run
ended".

Built with `new/2`, never a struct literal, so `macrostep`/`microstep`/
`round` are always stamped from the `Statifier.MachineState` at hand.

# `t`

```elixir
@type t() :: %Statifier.Effect.Trace.ExitSet{
  configuration: MapSet.t(non_neg_integer()),
  indexes: [non_neg_integer()],
  macrostep: non_neg_integer(),
  microstep: non_neg_integer(),
  round: non_neg_integer()
}
```

# `new`

```elixir
@spec new(machine_state :: Statifier.MachineState.t(), fields :: keyword()) :: t()
```

Stamps `macrostep`/`microstep`/`round` from `machine_state` and sets
`fields` (`:indexes`, `:configuration`).

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*Consult [api-reference.md](api-reference.md) for complete listing*