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machine.js

  // Available variables:
  // - Machine
  // - interpret
  // - assign
  // - send
  // - sendParent
  // - spawn
  // - raise
  // - actions
  // - XState (all XState exports)
  
  let NOT_SET = Symbol('NOT_SET')
  
  let abstractActions = {
      assignInput: assign({input: (_, ev) => ev.data}),
      assignOutput: assign({output: (_, ev) => ev.data}),
      assignError: assign({error: (_, ev) => ev.error}),
      notifyClean: () => console.log('clean'),
      notifyPiping: () => console.log('piping'),
      notifyPiped: () => console.log('piped'),
      notifyLeaking: () => console.warn('leak'),
      notifyEnded: () => console.log('ended'),
      clean: assign(['input', 'output', 'error'].reduce((acc, key) => ({...acc, [key]: NOT_SET}), {})),
      handleLeak: (_, ev) => console.error(ev),
      assemble: () => console.log('assemble'),
    },
    CLEAN = 'clean',
    ASSEMBLE = {
      actions: 'assemble',
    },
    PIPE_IN = {
      target: 'piping',
      actions: 'assignInput',
    },
    PIPE_OUT = {
      target: 'piped',
      actions: 'assignOutput',
    },
    LEAK = {
      target: 'leaked',
      actions: 'assignError',
    }
  
  let pipeMachineDef = {
    id: 'pipe',
    initial: 'clean',
    context: {
      input: NOT_SET,
      output: NOT_SET,
    },
    states: {
      clean: {
        entry: [
          'clean',
          'notifyClean'
        ],
        on: {
          ASSEMBLE,
          PIPE_IN,
        }
      },
      piping: {
        entry: 'notifyPiping',
        invoke: {
          id: 'piping',
          src: 'pipe',
          onDone: PIPE_OUT,
          onError: LEAK,
        }
      },
      leaked: {
        entry: [
          'notifyLeaking',
          'handleLeak',
        ],
        type: 'final',
      },
      piped: {
        entry: 'notifyPiped',
        type: 'final',
      },
    },
  }
  let pipe = input => input * 2
  let pipeMachineConfig = {
    actions: abstractActions,
    services: {
      pipe: ctx => Promise.resolve(pipe(ctx.input)),
    },
  }
  let pipeMachine = Machine(pipeMachineDef, pipeMachineConfig)