99 Elm 問題/問題 16/解決方案

解決方案 1：使用 List.foldr 和 List.indexedMap

dropEvery n list =
  let
    indexed = List.indexedMap (,) list
    maybeAdd (i, x) xs =
      if (i + 1) % n == 0 then xs else x :: xs        
  in
    List.foldr maybeAdd [] indexed