Add insert function

src/glearray.gleam

@@ -48,4 +48,19 @@ fn is_valid_index(array: Array(a), index: Int) -> Bool {
 
 @external(erlang, "erlang", "append_element")
 @external(javascript, "./glearray_ffi.mjs", "push")
-pub fn push(to array: Array(a), value value: a) -> Array(a)
+pub fn push(onto array: Array(a), value value: a) -> Array(a)
+
+pub fn insert(
+  into array: Array(a),
+  at index: Int,
+  value value: a,
+) -> Result(Array(a), Nil) {
+  case index >= 0 && index <= length(array) {
+    True -> Ok(do_insert(array, index, value))
+    False -> Error(Nil)
+  }
+}
+
+@external(erlang, "glearray_ffi", "insert")
+@external(javascript, "./glearray_ffi.mjs", "insert")
+fn do_insert(array: Array(a), index: Int, value: a) -> Array(a)

src/glearray_ffi.erl

@@ -1,9 +1,11 @@
 -module(glearray_ffi).
 
--export([new/0, at/2, set/3]).
+-export([new/0, at/2, set/3, insert/3]).
 
 new() -> {}.
 
 at(Array, Index) -> element(Index + 1, Array).
 
 set(Array, Index, Value) -> setelement(Index + 1, Array, Value).
+
+insert(Array, Index, Value) -> erlang:insert_element(Index + 1, Array, Value).

src/glearray_ffi.mjs

@@ -25,3 +25,7 @@ export function push(array, value) {
   copy.push(value);
   return copy;
 }
+
+export function insert(array, index, value) {
+  return array.toSpliced(index, 0, value);
+}

test/glearray_test.gleam

@@ -1,5 +1,6 @@
 import gleam/list
 import gleam/function
+import gleam/result
 import gleeunit
 import gleeunit/should
 import glearray.{type Array}
@@ -83,6 +84,22 @@ pub fn push_test() {
   |> should.equal([1, 2, 3])
 }
 
+pub fn insert_test() {
+  let array = glearray.from_list([1, 2, 3])
+  array
+  |> glearray.insert(at: 0, value: 9)
+  |> result.map(glearray.to_list)
+  |> should.equal(Ok([9, 1, 2, 3]))
+  array
+  |> glearray.insert(at: 2, value: -1)
+  |> result.map(glearray.to_list)
+  |> should.equal(Ok([1, 2, -1, 3]))
+  array
+  |> glearray.insert(3, 20)
+  |> result.map(glearray.to_list)
+  |> should.equal(Ok([1, 2, 3, 20]))
+}
+
 fn assert_empty(array: Array(a)) -> Array(a) {
   assert_length(array, 0)
   should.equal(array, glearray.new())