consumer.js

var store = new TaskStore(reducer, actions.init({
  tasks: {
    incomplete: incompleteTasks,
    complete: completedTasks,
  },
}));

store.state.observe(function (state) { console.log(state) });

store.js

(function () {
  'use strict';

  var empty = R.empty;

  function TaskStore () {
    var dispatcher = mostSubject.subject();

    return function constructor (reducer, initialState) {
      this.state = dispatcher
                     .scan(reducer, head(initialState))
                     .thru(mostHold.default);

      this.dispatch = dispatcher.next.bind(dispatcher);

      return this;
    };
  }

  angular
    .module('task')
    .factory('TaskStore', TaskStore);
}());