Promise/Future Result Maybe object!

gistfile1.md

The task

1. get something from a remote site (loadPage())
2. find specific element (findElement())
3. grab and parse contents as JSON (extractJson())

stage 1

Easy way: grab page and return result

const task = async url => {
  // loadPage :: String -> Promise Page
  const page = await loadPage(url)
  
  // findElement :: Page -> DomElement|Null
  const element = findElement(page)
  
  // extractJson :: DomElement -> Object|Null
  return element ? extractJson(element) : null
}

stage 2

findElement and extractJson can return null. It's a perfect case for Maybe !

const task = async url => {
  const page = await loadPage(url)
  
  // findElement :: Page -> Maybe DomElement
  // extractJson :: DomElement -> Maybe Object
  return findElement(page)
    .chain(extractJson)
}

stage 3

why should I stop on Maybe. There're more fancy things!

Looks like Task is the right one for the job.

// loadPage :: String -> Task Error Page

stage 4

Hmm.. should Task return data wrapped in Result? Sounds quite logical!

// loadPage :: String -> Task Error (Result ?? Page)

stage 5

Does Task should return Future... Don't think so. Actually Promise is a Future so I'm replacing Task with Future.

stage 6

So, I have a Future which should return Result. Value of Result will be parsed and wrapped in Maybe.

Doest it mean that my function returns Future (Result Error (Maybe object))? :o

stage 7

The complexity of this thing weighs heavily on my shoulders...

stage 8

Ahh! forgot that task() should return a promise. Way more complicated..

stage 9 - finale

Fuck it! Promise returning Maybe is all I need.
going back to stage 2

@i-am-tom : Thank you! I was sure that I should hold Maybe as a Data of Future (or, actually, Promise). Now it makes more sense. Thanks!