ADR 18: Keeping a single state #305
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ch1bo
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| * The interface between the `Hydra.Node` and a `Hydra.Chain` component consists of | ||
| - constructing certain Head protocol transactions given a description of it (`PostChainTx tx`): | ||
| ```hs | ||
| postTx :: MonadThrow m => PostChainTx tx -> m () |
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I don't think this first point is really about the interface between the Hydra.Node and the Hydra.Chain. This is really the client interface and how clients can interact with the on-chain state.
Nevermind. We do indeed use this handle as a mean between the two components, postChainTx calls are a result of effects emitted by the head logic in response to client inputs.
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Somehow I keep getting "confused" by this 🤔 ... Maybe just a naming question.
| * We provide the latest `ChainState tx` to `postTx` by extending `PostChainTx tx` | ||
| * We change the callback interface of `Chain` to | ||
| ```hs | ||
| type ChainCallback tx m = (ChainState tx -> Maybe (OnChainTx tx)) -> m () |
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This suggests that the ChainState tx may evolve separately from the an event occurrence. Is that the case 🤔 ?
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My bad, I missed the parentheses. The ChainState here would be provided by the logic layer. I wonder though if this can be achieved in a pure fashion 🤔 ... Intuitively, I feel like we'd need something like m (ChainState tx)
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As this is the core bit of the whole proposal, i did twiddle things around a bit and tested them on the https://github.com/input-output-hk/hydra-poc/compare/ch1bo/adr-18-single-state-example branch. Happy to walk you through the current proposed state and we can pair on making it simpler still maybe? :)
| ```hs | ||
| postTx :: MonadThrow m => ChainState tx -> PostChainTx tx -> m () | ||
| type ChainCallback tx m = (ChainState tx -> Maybe (OnChainTx tx, ChainState tx)) -> m () | ||
| ``` |
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I do highly prefer the alternative here ☝️ , as it:
- Keep the base types "simpler"
- Make more obvious from the type signature what is going on (typical state update
s -> (a, s)) - Maintain a clearer separation between the stateful part, and the somewhat stateless / deterministic bits which are the chain tx.
Co-authored-by: Matthias Benkort <[email protected]>
Co-authored-by: Matthias Benkort <[email protected]>
We decided to favor the non-extended "core types" in the Node/Chain interface as it's more explicit about ChainState updates.
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Drafted how we could keep a single TVar only by updating the interface between
Hydra.NodeandHydra.Chain.I tried to exercise (quick'n'dirty and not intending to be merged) this and the to-be-discussed alternative (see ADR) on these branches:
hydra-nodewith only some undefinedFixes #257