lattice/dot_context

A dot context tracks observed events (dots) across replicas.

A “dot” is a pair of (replica_id, counter) uniquely identifying a single write event. The dot context is used by causal CRDTs like MV-Register and OR-Set to determine which operations have been observed and which can be safely discarded during merge.

Example

import lattice/dot_context.{Dot}

let ctx = dot_context.new()
  |> dot_context.add_dot("node-a", 1)
  |> dot_context.add_dot("node-b", 1)
dot_context.contains_dots(ctx, [Dot("node-a", 1)])  // -> True

Types

Dot

</>

A unique identifier for a single write event at a specific replica.

replica_id identifies the replica that produced the event and counter is the replica’s logical clock value at the time of the write. Together they form a globally unique event identifier. Users construct Dot values when calling contains_dots or remove_dots.

pub type Dot {
  Dot(replica_id: String, counter: Int)
}

Constructors

```
Dot(replica_id: String, counter: Int)
```

DotContext

opaque </>

An opaque set of observed dots (write events).

Use new, add_dot, remove_dots, and contains_dots to interact with a DotContext. The internal set representation is hidden to allow future changes to the storage strategy.

pub opaque type DotContext

Values

add_dot

</>

pub fn add_dot(
  context: DotContext,
  replica_id: String,
  counter: Int,
) -> DotContext

Add a specific dot to the context.

Records that the event (replica_id, counter) has been observed. If the dot is already present, the context is returned unchanged.

contains_dots

</>

pub fn contains_dots(
  context: DotContext,
  dots: List(Dot),
) -> Bool

Check if all given dots are present in the context.

Returns True only if every dot in dots has been observed (i.e., every dot was previously added via add_dot and not subsequently removed). Returns True for an empty dots list.

new

</>

pub fn new() -> DotContext

Create a new empty DotContext.

Returns a context with no observed dots. Use add_dot to record events.

remove_dots

</>

pub fn remove_dots(
  context: DotContext,
  dots: List(Dot),
) -> DotContext

Remove a list of dots from the context.

Returns a new context with all dots in dots removed. Dots that are not present are silently ignored.