Module transform 

Transform operators (R5.7) — element-wise mappings and folds.

Mirrors the TS shapes in ~/src/graphrefly-ts/packages/pure-ts/src/extra/operators/transform.ts, but driven by Core dispatch (graphrefly_core::OperatorOp) instead of derived-fn factories. Per Slice C-1 / D009.

Each factory takes &Core, an &Arc<dyn OperatorBinding> (for registering the user closure), the source node id, the user-supplied callback, and any operator-specific arguments (seeds for folders). The factory:

1. Registers the user closure on the binding (returns a FnId).
2. Calls Core::register_operator with the appropriate OperatorOp variant.
3. Returns an OperatorRegistration carrying the new node id and (for folders) the registered seed handle.

Refcount discipline

For scan and reduce, the seed handle ownership transfers from the caller’s binding-side intern into Core’s ScanState / ReduceState (post-Slice C-3 / D026 — generic op_scratch slot replaces the typed operator_state field). Core takes one retain via [BindingBoundary::retain_handle] inside register_operator; the caller is expected to retain a share for themselves if they want to reference the seed elsewhere.

Structs

OperatorRegistration

Output of an operator factory call. Carries the new operator node id plus operator-specific context (e.g., the registered closure’s FnId for traceability / debugging).

Functions

distinct_until_changed

distinctUntilChanged(source, equals) — suppresses adjacent duplicates.

distinct_until_changed_with

distinct_until_changed with explicit OperatorOpts.

filter

filter(source, predicate) — silent-drop selection (D012/D018).

filter_with

filter with explicit OperatorOpts.

map

map(source, project) — element-wise transform.

map_with

map with explicit OperatorOpts.

pairwise

pairwise(source) — emits (prev, current) pairs starting after the second value. First value is swallowed (used as prev).

pairwise_with

pairwise with explicit OperatorOpts.

reduce

reduce(source, fold, seed) — left-fold emitting once on upstream COMPLETE.

reduce_with

reduce with explicit OperatorOpts.

scan

scan(source, fold, seed) — left-fold emitting each new accumulator.

scan_with

scan with explicit OperatorOpts.