# `permchain`

## Get started

`pip install permchain`

## Usage

```python
from permchain import Pregel, channels

grow_value = (
    Pregel.subscribe_to("value")
    | (lambda x: x + x)
    | Pregel.write_to(value=lambda x: x if len(x) < 10 else None)
)

app = Pregel(
    chains={"grow_value": grow_value},
    channels={"value": channels.LastValue(str)},
    input="value",
    output="value",
)

assert app.invoke("a") == "aaaaaaaa"

```

Check `examples` for more examples.

## Near-term Roadmap

- [x] Iterate on API
  - [x] do we want api to receive output from multiple channels in invoke()
  - [x] do we want api to send input to multiple channels in invoke()
  - [x] Finish updating tests to new API
- [x] Implement input_schema and output_schema in Pregel
- [ ] More tests
  - [x] Test different input and output types (str, str sequence)
  - [x] Add tests for Stream, UniqueInbox
  - [ ] Add tests for subscribe_to_each().join()
- [x] Add optional debug logging
- [ ] Implement checkpointing
  - [ ] Save checkpoints at end of each step
  - [ ] Load checkpoint at start of invocation
  - [ ] API to specify storage backend and save key
- [ ] Add more examples
  - [ ] human in the loop
  - [ ] combine documents
  - [ ] agent executor
  - [ ] run over dataset
- [ ] Fault tolerance
  - [ ] Retry individual processes in a step
  - [ ] Retry entire step?
- [ ] Pregel.stream_log to contain additional keys specific to Pregel
  - [ ] tasks: inputs of each chain in each step, keyed by {name}:{step}
  - [ ] task_results: same as above but outputs
  - [ ] channels: channel values at end of each step, keyed by {name}:{step}