The architecture

The layers

Each package imports only from the layers under it. The dependencies of the package files enforce the order.

The core layers, and the two standalone packages (dashed). The viewer also uses pack for its layout.

The flow of data

1. hydrate makes an instance tree from a value. Each instance has a root container whose slots are its cells.
2. The store evaluates all new nodes in one epoch.
3. splay renders the tree with the render methods of the classes, through a memo.
4. An edit writes a cell (setValue). The store starts one ordered epoch over the readers of the cell.
5. The host deletes the memo entries of the changed instances and renders again.
6. For a user class, the edit also changes the class, and updateClass sends it to the other instances.

The invariants

Invariant	Who keeps it
The value of each node is the evaluation of its expression	Each write starts an epoch, or a batch starts one at its end
The seats agree with the reads	The flush rewires each touched node
The expression of a container is the record of its slots	setSlot, expandNode and the removal make the record again
Each slot points at a node of the store	removeNode detaches each slot of each holder
A node outside a cycle evaluates at most one time in an epoch	The topological order of the components of the closure
A write is not reverted	A write changes the expression, and the value comes from the expression

The decisions

The decisions record each choice and its reason. The review records each defect that the October review found, with the live status of its regression test.