docs: function main(sources) {
      let nextDialog$ = sources.Dialog
  	    .filter(({id}) => id == 'first')
  	    .map(x => ({
  		method: 'alert',
  		options: {
  		    message: 'result value:' + x.value
  		}
  	    }));
  
      let dialog$ = Rx.Observable.just({
  	id: 'first',
  	method: 'prompt',
          options: {
  	    message: 'hello cycle.js',
  	    placeholder: 'input'
  	}
      }).merge(nextDialog$);
      return {
  	Dialog: dialog$
      };
  }