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# Statifier
[](https://github.com/riddler/statifier-ex/actions/workflows/ci.yml)
[](https://hex.pm/packages/statifier)
[](https://hex.pm/packages/statifier)
[](https://hexdocs.pm/statifier/)
[](https://github.com/riddler/statifier-ex/blob/main/LICENSE)
A W3C SCXML-conformant statecharts engine for Elixir. Ground-up rewrite of
[statifier](https://github.com/riddler/statifier) v1.x, built against the SCION
and W3C conformance corpora from day one.
## Why a rewrite
v1 works, but its interpreter re-derived the SCXML semantics instead of porting
the spec's algorithm, and the divergences account for nearly all of its remaining
conformance failures. v2 is:
- a **literal port of W3C SCXML Appendix D** - same functions, same names
- a **pure functional core** returning effects - one semantics for every API,
sessions and timers layered on top
- **predicator as the datamodel** - safe, non-evaluative expressions; no
ECMAScript, no eval
- built **corpus-first** - 281 generated SCION/W3C conformance tests (119
SCION + 162 W3C) behind a forward-only regression ratchet inherited from
v1, with the generator committed this time
## Installation
Add `statifier` to your dependencies:
```elixir
def deps do
[
{:statifier, "~> 2.3"}
]
end
```
Releases follow [SemVer](https://semver.org); [CHANGELOG.md](CHANGELOG.md)
is the upgrade briefing, and its `[2.0.0]` section is written as a migration
document for 1.x users. (The pre-release SHA-pinning contract ended with
2.0.0 - [ADR-0066](https://github.com/riddler/statifier-ex/blob/main/docs/adr/0066-publishes-2-0-0-ending-the-sha-pinning-contract.md).)
Persisted position and recording blobs refuse with a typed error on a
format-version or chart-identity mismatch rather than misreading.
## Quick start
Compile an SCXML document, initialize it, and send it events. Here is a card
authorization that checks the amount against a budget before capturing it:
```elixir
source = """
<scxml xmlns="http://www.w3.org/2005/07/scxml" version="1.0"
datamodel="predicator" initial="authorizing">
<datamodel>
<data id="amount" expr="4200"/>
<data id="budget_remaining" expr="10000"/>
</datamodel>
<state id="authorizing">
<transition event="card.approved" cond="amount <= budget_remaining"
target="capturing"/>
<transition event="card.approved" target="over_budget"/>
<transition event="card.declined" target="declined"/>
</state>
<state id="capturing">
<invoke type="myapp:capture" id="capture">
<param name="amount" expr="amount"/>
</invoke>
<transition event="done.invoke.capture" target="settled"/>
<transition event="error.communication" target="needs_attention"/>
</state>
<state id="over_budget"/>
<state id="declined"/>
<state id="needs_attention"/>
<final id="settled"/>
</scxml>
"""
{:ok, machine} = Statifier.compile(source)
{machine_state, _effects} = Statifier.initialize(machine)
Statifier.active_leaf_states(machine_state)
#=> MapSet.new(["authorizing"])
{:ok, machine_state, effects} = Statifier.send_event(machine_state, "card.approved")
Statifier.active_leaf_states(machine_state)
#=> MapSet.new(["capturing"])
```
The guard is a [predicator](https://github.com/riddler/predicator-ex)
expression evaluated against the chart's own datamodel - no ECMAScript and no
`eval`. Because `4200 <= 10000` held, the run took the first arrow.
Effects come back as data; the engine never performs them for you. Entering
`capturing` did not call your payment service, it described the call:
```elixir
effects
#=> [
#=> invoke: %Statifier.Effect.Invoke{
#=> invoke_id: "capture",
#=> type: "myapp:capture",
#=> params: %{"amount" => 4200},
#=> ...
#=> }
#=> ]
```
Performing that effect is your host's job, and so is telling the chart how it
went: `Statifier.Session.done_invocation/3` delivers
`done.invoke.capture`, and `Statifier.Session.failed_invocation/3` delivers
`error.communication.invoke.capture` once your retry policy is exhausted -
which is the arrow that parks this run in `needs_attention` instead of waiting
in `capturing` forever. See [Extending](docs/extending.md).
That four-function surface (`compile/2`, `initialize/2`, `send_event/2`,
`active_leaf_states/1`) is the whole entry point; sessions, durable timers,
persistence, and telemetry layer on top of it.
## Documentation
Published guides on [hexdocs](https://hexdocs.pm/statifier/):
- [Architecture](docs/architecture.md) - the layered design and the
decisions behind it
- [Datamodel](docs/datamodel.md) - predicator expressions, `<data>`,
`<assign>`, and `<script>`
- [Extending](docs/extending.md) - registering your own `<invoke>` handlers,
and reporting completion or permanent failure back to the chart
- [Persistence](docs/persistence.md) - chart identity, persisted positions,
and resuming sessions
- [Durable timers](docs/durable-timers.md) - scheduling delayed sends
outside the session process
- [Observability](docs/observability.md) - trace effects and what to do
with them
- [OpenTelemetry](docs/opentelemetry.md) - span topology and the OTel bridge
- [Testing charts](docs/testing-charts.md) - testing your own state charts
- [Chart patterns](docs/chart-patterns.md) - patterns for
external-resource verdicts (park/retry, fail-fast)
- [Family reference](docs/family-reference.md) - what the statifier sibling
repos copy from here
Architecture Decision Records live in the repository at
[docs/adr/](https://github.com/riddler/statifier-ex/blob/main/docs/adr/README.md).
## Development
```bash
mix deps.get
mix quality --profile loop # fast inner loop
mix quality # full gate (required green before commit)
```
Issue tracking is [beads](https://github.com/gastownhall/beads) (`bd ready` to
find work). Workflow, model roles, and worktree conventions:
[docs/workflow.md](https://github.com/riddler/statifier-ex/blob/main/docs/workflow.md).
## License
MIT - see [LICENSE](https://github.com/riddler/statifier-ex/blob/main/LICENSE).