# `ExTLA.GenServer.Violation`
[🔗](https://github.com/dcoai/extla/blob/v0.6.0/lib/ex_tla/gen_server/violation.ex#L1)

A Layer 3 conformance failure: the implementation took a step its specification does not
permit, or reached an abstract state the specification forbids.

`kind` is the finding, and the message is the layer's primary output:

| `kind` | Meaning |
|---|---|
| `:not_enabled` | the action's guard was false on the pre-state — the implementation did what the spec forbids there |
| `:diverged` | the guard held, but no binding of the action's params reproduces the implementation's post-state |
| `:unmapped_but_moved` | no action was claimed, yet the abstract state changed |
| `:invariant` | the abstract post-state violates one of the spec's invariants |
| `:action_property` | the abstract transition violates one of the spec's action properties |

`:diverged` is the common one, and it is more often the **refinement mapping** that is
wrong than the implementation. That is still a finding worth having: a mapping that does
not track the implementation invalidates every other check in the layer.

# `t`

```elixir
@type t() :: %ExTLA.GenServer.Violation{
  __exception__: term(),
  action: atom() | nil,
  detail: String.t() | nil,
  diff: [{atom(), term(), term()}] | nil,
  kind:
    :not_enabled
    | :diverged
    | :unmapped_but_moved
    | :invariant
    | :action_property,
  name: atom() | nil,
  params: map() | nil,
  post: ExTLA.State.t() | nil,
  pre: ExTLA.State.t() | nil,
  spec: module()
}
```

---

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