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machine.js

const isGasable = (context) => context.temperature >= 100
const isFreezable = (context) => context.temperature < 0
const isLiquidable = (context) => context.temperature > 0 && context.temperature < 100

const waterMachine = Machine({
  id: 'waterMachine',
  initial: 'ice',
  context: {
    temperature: 0
  },
  states: {
    ice: {
      on: {
        FUSION: {target:'liquid', cond: isLiquidable},
        SUBLIMATION: {target:'gas', cond: isGasable}
      }
    },
    liquid: {
      on: {
        SOLIDIFICATION: 'ice',
        VAPORISATION: 'gas'
      }
    },
    gas: {
      on: {
        CONDENSATION: 'ice',
        LIQUEFACTION: 'liquid'
      }
    },
  },
  on: {
    INCREASE_ROOM_TEMPERATURE: {
      actions: assign({ temperature: (context) => context.temperature + 10 })
    },
    DECREASE_ROOM_TEMPERATURE: {
      actions: assign({ temperature: (context) => context.temperature - 10 })
    }
  }
});