Add set function

src/glearray.gleam

@@ -17,7 +17,7 @@ pub fn to_list(array: Array(a)) -> List(a)
 pub fn length(of array: Array(a)) -> Int
 
 pub fn at(in array: Array(a), get index: Int) -> Result(a, Nil) {
-  case index >= 0 && index < length(array) {
+  case is_valid_index(array, index) {
     True -> Ok(do_at(array, index))
     False -> Error(Nil)
   }
@@ -26,3 +26,22 @@ pub fn at(in array: Array(a), get index: Int) -> Result(a, Nil) {
 @external(erlang, "glearray_ffi", "at")
 @external(javascript, "./glearray_ffi.mjs", "at")
 fn do_at(array: Array(a), index: Int) -> a
+
+pub fn set(
+  in array: Array(a),
+  at index: Int,
+  value value: a,
+) -> Result(Array(a), Nil) {
+  case is_valid_index(array, index) {
+    True -> Ok(do_set(array, index, value))
+    False -> Error(Nil)
+  }
+}
+
+@external(erlang, "glearray_ffi", "set")
+@external(javascript, "./glearray_ffi.mjs", "set")
+fn do_set(array: Array(a), index: Int, value: a) -> Array(a)
+
+fn is_valid_index(array: Array(a), index: Int) -> Bool {
+  index >= 0 && index < length(array)
+}

src/glearray_ffi.erl

@@ -1,7 +1,9 @@
 -module(glearray_ffi).
 
--export([new/0, at/2]).
+-export([new/0, at/2, set/3]).
 
 new() -> {}.
 
 at(Array, Index) -> element(Index + 1, Array).
+
+set(Array, Index, Value) -> setelement(Index + 1, Array, Value).

src/glearray_ffi.mjs

@@ -13,3 +13,9 @@ export function arrayLength(array) {
 export function at(array, index) {
   return array[index];
 }
+
+export function set(array, index, value) {
+  const copy = [...array];
+  copy[index] = value;
+  return copy;
+}

test/glearray_test.gleam

@@ -27,7 +27,7 @@ pub fn from_to_list_test() {
 }
 
 pub fn at_test() {
-  let list = ["a", "B", "fdsau", "rh3892wfd", "äèëå亣", "Another ONE!"]
+  let list = ["a", "B", "fdsau", "rh3892wfd", "äèëå亣"]
   let array = glearray.from_list(list)
   list.index_map(
     list,
@@ -44,6 +44,26 @@ pub fn at_test() {
   |> should.be_error
   glearray.at(array, 100)
   |> should.be_error
+  glearray.at(glearray.new(), 0)
+  |> should.be_error
+}
+
+pub fn set_test() {
+  let array = glearray.from_list([1, 2, 3, 4])
+  let assert Ok(modified) = glearray.set(in: array, at: 1, value: 10)
+  array
+  |> glearray.to_list
+  |> should.equal([1, 2, 3, 4])
+  modified
+  |> glearray.to_list
+  |> should.equal([1, 10, 3, 4])
+
+  glearray.set(array, -1, 0)
+  |> should.be_error
+  glearray.set(array, glearray.length(array), 0)
+  |> should.be_error
+  glearray.set(glearray.new(), 0, 0)
+  |> should.be_error
 }
 
 fn assert_empty(array: Array(a)) -> Array(a) {