// Available variables:
  // - Machine
  // - interpret
  // - assign
  // - send
  // - sendParent
  // - spawn
  // - raise
  // - actions
  // - XState (all XState exports)
  
  const fetchMachine = Machine({
    id: 'fetch',
    initial: 'active',
    
    context: {
      past: [],
      current: null,
      queue: [1, 2, 3]
    },
    
    states: {
      active: {
        type: "parallel",
        
        states: {
          past: {
            initial: "empty",
            states: {
              empty: {},
              filled: {}
            }
          },
          current: {
            initial: "empty",
            states: {
              empty: {},
              filled: {}
            }
          },
          queue: {
            initial: "empty",
            states: {
              empty: {},
              filled: {
                on: {
                  MOVE: {
                    target: "empty",
                    actions: assign({}),
                    cond: "hasNext"
                  }
                }
              }
            }
          }
        }
      }
    }
  }, {
    guards: {
      hasCurrent: context => !!context.current,
      hasNext: context => context.queue.length > 0
    }
  });