Array vs List in Elm

Question

I was suprised to learn that Array and List were two different types in Elm:

• Array

• List

In my case,

Answer 1

Something like this should work:

import Array
import Debug

fromJust : Maybe a -> a
fromJust x = case x of
    Just y -> y
    Nothing -> Debug.crash "error: fromJust Nothing"

selectFromList : List a -> List Int -> List a
selectFromList els idxs = 
  let arr = Array.fromList els
   in List.map (\i -> fromJust (Array.get i arr)) idxs

It converts the input list to an array for fast indexing, then maps the list of indices to their corresponding values in the array. I took the fromJust function from this StackOverflow question.