| Safe Haskell | None |
|---|---|
| Language | Haskell2010 |
CRDT.Cm
- class (Observe payload, Eq (Observed payload), PartialOrd update) => CmRDT payload op update | payload -> op, op -> update, update -> payload where
- concurrent :: PartialOrd a => a -> a -> Bool
Documentation
class (Observe payload, Eq (Observed payload), PartialOrd update) => CmRDT payload op update | payload -> op, op -> update, update -> payload where Source #
Operation-based, or commutative (Cm) replicated data type.
Implementation
In Haskell, a CmRDT implementation consists of 3 types —
a payload, an operation (op) and an update.
- Payload
- Internal state of a replica.
- Operation
- User's request to update.
- Update
- Operation to be applied to other replicas.
For many types operation and update may be the same.
But for LWW, for instance, this rule doesn't hold:
user can request only value, and type attaches a timestamp to it.
Additional constraint — commutativity law
Concurrent updates are observed equally.
∀ up1 up2 s .concurrentup1 up2 ==>observe(updateDownstreamup1 .updateDownstreamup2 $ s) ==observe(updateDownstreamup2 .updateDownstreamup1 $ s)
Idempotency doesn't need to hold.
Minimal complete definition
Methods
updateAtSourcePre :: op -> payload -> Bool Source #
Precondition for updateAtSource.
Calculates if the operation is applicable to the current state.
updateAtSource :: Clock m => op -> m update Source #
Generate an update to the local and remote replicas.
Doesn't have sense if updateAtSourcePre is false.
May or may not use clock.
updateDownstream :: update -> payload -> payload Source #
Apply an update to the payload. An invalid update must be ignored.
concurrent :: PartialOrd a => a -> a -> Bool Source #
Not comparable, i. e. ¬(a ≤ b) ∧ ¬(b ≤ a).