block7.ts

const checkIsUploadingState = (state: State) =>
  state.tag === 'Uploading';
const checkIsNewState = (a: State, b: State) =>
  a.tag === b.tag;

const epic: Epic<Action, Action, State> = (
  action$,
  state$
) => {
  const stateEntry$ = state$.distinctUntilChanged(
    checkIsNewState
  );
  const uploadingStateEntry$ = stateEntry$.filter(
    checkIsUploadingState
  );

  const uploadRequest$ = uploadingStateEntry$.mergeMap(
    upload
  );

  // … return actions based on request
};