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Discussion on: Basic monads in Javascript

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edwilliams profile image
Ed Williams

This looks a excellent library; looking forward to using this. Could you help with the following example?

const data = [
  { wrongName: 'Jason', level: 7, cool: true },
  { wrongName: 'Blanche', level: 8, cool: false }
]

Maybe(data)
  .map(people => people.filter(person => person.cool))
  .map(people => people[0])
  .map(person => person.name)
  .map(name => name.toUpperCase())
  .cata({
    Just: data => console.log(data), // JASON
    Nothing: () => console.log('No data available')
  })

this appears to give me a Uncaught TypeError: Cannot read property 'toUpperCase'... but I imagined it might deal with the error in a similar way to Promises

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rametta profile image
Jason Author

For this example the following would be better if you weren't sure if some fields would be available

const data = [
  { wrongName: 'Jason', level: 7, cool: true },
  { wrongName: 'Blanche', level: 8, cool: false }
]

Maybe(data)
  .map(people => people.filter(person => person.cool))
  .chain(head)
  .chain(get(['name']))
  .map(name => name.toUpperCase())
  .cata({
    Just: data => console.log(data), // JASON
    Nothing: () => console.log('No data available')
  })
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yurakostin profile image
Yuri Kostin

It seems to looks better with Ramda, isn't it:

const data = [
  { wrongName: 'Jason', level: 7, cool: true },
  { wrongName: 'Blanche', level: 8, cool: false }
];

Maybe(data)
  .map(filter(propEq('cool', true)))
  .map(head)
  .map(prop('name'))
  .map(toUpper)
  .cata({
    Just: console.log
    Nothing: () => console.log('No data available')
  })

PS: thanks a lot for the article

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rametta profile image
Jason Author

This isn't exactly the same because Ramdas prop() does not return a Maybe, so if that prop did not exist then ramda would return an undefined, which will cause problems down the line. Same with head()

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yurakostin profile image
Yuri Kostin

You are totally right. Sorry for my mistake.