aquavm/crates/air-lib/trace-handler/README.md
Mike Voronov 24f0d66bed
Rename subtree to subgraph (#265)
Intially, a fold instruction was designed based on idea that its iterable can't expand,
so AIR was considered as a subtree. But after introducing recursive streams in #225, it's
no more a subtree, but a subgraph.
2022-05-17 15:53:33 +03:00

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## AIR trace handler
This crate contains implementation of the CRDT-based merging data algorithm. It exposes the `TraceHandler` struct that based on the visitor pattern and has public methods that should be called in certain places of AIR instructions execution. Internally `TraceHandler` contains several FSM and each of such public methods does state transitioning of one or more these FSMs. Below are state transition sequences for all instructions that caller must follow.
### Ap instruction
Expected sequence of `TraceHandler` calls for the `ap` instruction:
```
meet_ap_start
-> meet_ap_end
```
### Call instruction
Expected sequence of `TraceHandler` calls for the `call` instruction:
```
meet_call_start
-> meet_call_end
```
### Par instruction
Expected sequence of `TraceHandler` calls for the `par` instruction:
```
meet_par_start
-> meet_par_subgraph_end(..., SubgraphType::Left)
-> meet_par_subgraph_end(..., SubgraphType::Right)
```
### Fold instruction
Expected sequence of `TraceHandler` calls for the `fold` instruction:
```
meet_fold_start.1 ->
meet_generation_start.N ->
meet_next.M ->
meet_prev.M ->
meet_generation_end.N ->
meet_fold_end.1
```
where .T means that this function should be called exactly T times.