1 files changed, 12 insertions, 0 deletions
diff --git a/aoc-2020-gleam/src/ext/listx.gleam b/aoc-2020-gleam/src/ext/listx.gleam
index bead987..2d4f4b6 100644
--- a/aoc-2020-gleam/src/ext/listx.gleam
+++ b/aoc-2020-gleam/src/ext/listx.gleam
@@ -6,3 +6,15 @@ pub fn count(list: List(a), satisfying predicate: fn(a) -> Bool) -> Int {
   |> iter.from_list
   |> iterx.count(satisfying: predicate)
 }
+
+fn set_helper(list: List(a), value: a, index: Int, counter: Int) -> List(a) {
+  case list {
+    [] -> []
+    [_, ..t] if counter == index -> [value, ..t]
+    [h, ..t] -> [h, ..set_helper(t, value, index, counter + 1)]
+  }
+}
+
+pub fn set(list: List(a), value: a, at index: Int) -> List(a) {
+  set_helper(list, value, index, 0)
+}