map a key-value object to an operation

atom-operation-map.ts

export function* map<A>(slice: Slice<Record<string, A>>, operation: (slice: Slice<A>) => Operation<void>): Operation<void> {
  let contexts = new Map<string,Context>();

  function* synchronize(record: Record<string, A>) {
    let keep = new Set<string>();

    for (let key of Object.keys(record)) {
      if (!contexts.has(key)) {
        contexts.set(key, yield spawn(operation(slice.slice(key))))
      }
      keep.add(key);
    }

    for (let [key, context] of contexts.entries()) {
      if (!keep.has(key)) {
        context.halt();
      }
    }
  }

  yield synchronize(slice.get());

  yield subscribe(slice).forEach(synchronize);
}