Proposal: traversal filterWithIndex

[kylegoetz]

🚀 Feature request

that Traversal have a filterWithIndex in addition to filter

Current Behavior

A non-behavior because the feature does not exist.

Desired Behavior

I would like Traversal<S,A> to have filterWithIndex: <I>(f: Predicate<I>) => (sa:Traversal<S,A>) => Traversal<S,A>

Suggested Solution

I still am trying to figure out how the traversal code works, so I can't provide a suggested solution (yet). Is it theoretically possible/desired?

Who does this impact? Who is this for?

Additional context

Motivating use case: I'm porting some old, very convoluted code over to a more functional style and at one point it has something like

let spec = {}
Object.keys(obj).forEach(k => {
  if(['description', 'value', 'type'].indexOf(k) === -1) {
    spec[k] = obj[k].map(mappingFunction)
  }
})

It seems this would be nice:

const spec = objectTraversal
    .filterWithIndex((k,v) => ['description','value','type'].indexOf(k)===-1)
    .modify(mappingFunctioN)

[kylegoetz]

Note: I meant PredicateWithIndex<A> not Predicate<I>