CODEWITHSUNDEEP
javascriptfunctional-programmingramda.js
corvid
corvid

Reputation: 11197

ramda: set object based on the current state of the object

I want to have a pipeline which will set up a location object. Suppose the location object looks as follows to start:

{
  pathname: '/users',
  search: 'sort=desc&sortBy=name',
  hash: '',
  state: {},
}

On step one of the pipeline, I want to set the state.redirect of this to be the current object, but without the state included. e.g.,

{
  pathname: '/users',
  search: 'sort=desc&sortBy=name',
  hash: '',
  state: {
    redirect: {
      pathname: '/users',
      search: 'sort=desc&sortBy=name',
      hash: '',
    }
  }
}

I started with the following, but it didn't really work.

set(lensProp('state'), /* ??? */)

what's the appropriate way to do this in ramda?

Upvotes: 0

Views: 73

Answers (2)

Matías Fidemraizer
Matías Fidemraizer

Reputation: 64943

What about the following approach?

const input = {
  pathname: '/users',
  search: 'sort=desc&sortBy=name',
  hash: '',
  state: {},
}

const { lensProp, set, over, dissoc, pipe } = R

// The W combinator to apply twice the same input to a binary function
// W :: (a -> a -> b) -> a -> c
const W = f => x => f (x) (x)

// stateLens :: a -> b
const stateLens = lensProp ('state')

// Note how W will apply the input twice: it'll set the input
// to 'state' property!
// setSelfState :: (Object -> Object -> Object) -> Object -> Object
const setSelfState = W (set (stateLens))

// dissocInnerState :: Object -> Object
const dissocInnerState = over (stateLens) (dissoc ('state'))

// setSelftState :: Object -> Object
const setSelfState_ = pipe (
  setSelfState,
  dissocInnerState
)

const output = setSelfState_ (input)

console.log (output)
<script src="//cdnjs.cloudflare.com/ajax/libs/ramda/0.25.0/ramda.js"></script>

Upvotes: 0

Scott Sauyet
Scott Sauyet

Reputation: 50807

This should do it:

const loc = {
  pathname: '/users',
  search: 'sort=desc&sortBy=name',
  hash: '',
  state: {},
}

console.log(R.dissoc('state', loc))
<script src="//cdnjs.cloudflare.com/ajax/libs/ramda/0.25.0/ramda.js"></script>

Ramda's What Function Should I Use? might help find functions like this.

Upvotes: 1

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