# `StatifierBlocks.Describe.Edge`
[🔗](https://github.com/riddler/statifier_blocks/blob/v0.44.1/lib/statifier_blocks/describe/edge.ex#L1)

One way control passes between blocks in a `StatifierBlocks.Describe`
outline, in the vocabulary of the package's note on the block-level flow
graph, `docs/block-level-flow-graph.md` (ADR-0016 decision 1).

`container` is the block whose structure produced the edge. An endpoint
names a block and which part of it the edge touches: `{:block, id}` the
block itself, `{:entry, id}` and `{:exit, id}` a container's entry and
exit, and `{:body, id}` a group's body.

| `kind` | From | To | Carries |
|---|---|---|---|
| `:entry` | `{:entry, container}` | the first child, or `{:exit, container}` for an empty body | nothing |
| `:sequence` | a child | the next child in the same slot | `outcomes` |
| `:exit` | the last child of a slot | `{:exit, container}` | `outcomes` |
| `:branch` | `{:entry, branch}` | an arm's first child, or `{:exit, branch}` for an empty arm | `condition` |
| `:interrupt` | a handler | `{:exit, group}` to abandon, `{:body, group}` to resume | `event`, `history` |
| `:timer` | a delayed `core.send` | `{:block, id}`, a `core.on_event` or `core.await` naming the sent event | `event`, `delay` |

`outcomes` is every outcome name the source block's type declares, on
the one edge. `condition` is the arm's condition as its config holds it
(`nil` when none is written), `:otherwise`, or `:undecided`. `history` is
`:shallow` or `:deep` for a resume into a `core.resumable_group`, and
`nil` otherwise: a resume into a `core.group` restarts its body from the
first step.

A `:timer` edge is the one edge that joins two blocks by an event name
(ADR-0016's amendment of 2026-09-27, ADR-0017 decision 3): it is not a
transition, it says that the send arms an event the other block waits
for. Its `container` is the send's parent, `event` is the sent event, and
`delay` is the send's delay as its config holds it, the edge's label.
`delay` is `nil` on every other kind of edge.

# `condition`

```elixir
@type condition() :: String.t() | :otherwise | :undecided | nil
```

# `endpoint`

```elixir
@type endpoint() ::
  {:block, StatifierBlocks.Block.id()}
  | {:entry, StatifierBlocks.Block.id()}
  | {:exit, StatifierBlocks.Block.id()}
  | {:body, StatifierBlocks.Block.id()}
```

# `kind`

```elixir
@type kind() :: :entry | :sequence | :exit | :branch | :interrupt | :timer
```

# `t`

```elixir
@type t() :: %StatifierBlocks.Describe.Edge{
  condition: condition(),
  container: StatifierBlocks.Block.id(),
  delay: String.t() | nil,
  event: String.t() | nil,
  from: endpoint(),
  history: :shallow | :deep | nil,
  kind: kind(),
  outcomes: [String.t()],
  to: endpoint()
}
```

---

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