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machine.js

const echoCallbackHandler = (context, event) => (callback, onEvent) => {
  onEvent(({ type }) => {
    if(type === 'HEAR') {
     callback('ECHO')  
    }
  })
}
  
const echoMachine = Machine({
  id: 'echo',
  initial: 'listening',
  states: {
    listening: {
      invoke: {
        id: 'echoCallback',
        src: echoCallbackHandler,
      },
      on: {
       SPEAK: {
         actions: send('HEAR', {
           to: 'echoCallback'
         })
       },
        ECHO: {
          actions: () => {
            console.log('echo, echo')
          }
        } 
      }
    }
  }
});