· Unison programming language

📓 Implement functions with Ability operations

rangeAverage : Nat ->{Store [Nat]} Float
rangeAverage n = base.todo "implement me"

Using the Store ability to keep track of a List of numbers, write a function which takes in some number n of Nat as an upper bound of a list from 0 up to (but not including) n and returns the average of the final list.

So, given an upper value of 5, the average produced would be the average of [0, 1, 2, 3, 4], or 2.0

🔑 Answer

One possible solution is as follows:

averageOfRange : Nat ->{Store [Nat]} Float

averageOfRange : Nat ->{Store [Nat]} Float
averageOfRange n =
  use Float / fromNat
  use List +:
  use Nat + ==
  go = cases
    i 
      | i == n    ->
        myList = Store.get
        listSize = List.size myList
        sum = List.foldLeft (acc element -> element + acc) 0 myList
        fromNat sum / fromNat listSize
      | otherwise ->
        Store.modify (currentList -> i +: currentList)
        go (i + 1)
  go 0