daggy_machine.js

var daggy = require('daggy')

const Machine = daggy.taggedSum('Timer', {
  Yellow: [],
  Green: [],
  Red: []
})

Machine.prototype.timer =
  function () {
    return this.cata({
      Green: () => Machine.Yellow,
      Yellow: () => Machine.Red,
      Red: () => Machine.Green,
    })
  }


var machine = Machine.Red
console.log(machine.toString())

machine = machine.timer()
console.log(machine.toString())

machine = machine.timer()
console.log(machine.toString())

machine = machine.timer()
console.log(machine.toString())