Array index

4 files changed, 34 insertions, 1 deletions

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 2b4892c..1c049cb 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -3,4 +3,4 @@
 ## Unreleased
 
 - The `array` module was created with the `Array(element)` type and `to_list`,
-  `from_list`, `map`, `fold`, `fold_right`, and `length` functions.
+  `from_list`, `map`, `fold`, `fold_right`, `get`, and `length` functions.
diff --git a/src/ffi.js b/src/ffi.js
index 81362bb..c0b2076 100644
--- a/src/ffi.js
+++ b/src/ffi.js
@@ -1,3 +1,5 @@
+import { Ok, Error } from "./gleam.js";
+
 export function toArray(list) {
   return list.toArray();
 }
@@ -17,3 +19,7 @@ export function reduce(thing, acc, fn) {
 export function reduceRight(thing, acc, fn) {
   return thing.reduceRight(fn, acc);
 }
+
+export function index(thing, index) {
+  return index in thing ? new Ok(thing[index]) : new Error(undefined);
+}
diff --git a/src/gleam/javascript/array.gleam b/src/gleam/javascript/array.gleam
index 0895ff1..4b59b85 100644
--- a/src/gleam/javascript/array.gleam
+++ b/src/gleam/javascript/array.gleam
@@ -1,3 +1,5 @@
+// TODO: docs
+// TODO: labels
 pub external type Array(element)
 
 pub external fn to_list(Array(element)) -> List(element) =
@@ -17,3 +19,6 @@ pub external fn fold(Array(e), a, fn(a, e) -> a) -> a =
 
 pub external fn fold_right(Array(e), a, fn(a, e) -> a) -> a =
   "../../ffi.js" "reduceRight"
+
+pub external fn get(Array(e), Int) -> Result(e, Nil) =
+  "../../ffi.js" "index"
diff --git a/test/gleam/javascript/array_test.gleam b/test/gleam/javascript/array_test.gleam
index ccebcc7..6e8599c 100644
--- a/test/gleam/javascript/array_test.gleam
+++ b/test/gleam/javascript/array_test.gleam
@@ -69,3 +69,25 @@ pub fn fold_right_test() {
     |> array.from_list
     |> array.fold_right([], fn(a, e) { [e, ..a] })
 }
+
+pub fn index_test() {
+  assert Ok(1) =
+    [1, 2]
+    |> array.from_list
+    |> array.get(0)
+
+  assert Ok(2) =
+    [1, 2]
+    |> array.from_list
+    |> array.get(1)
+
+  assert Error(Nil) =
+    [1, 2]
+    |> array.from_list
+    |> array.get(2)
+
+  assert Error(Nil) =
+    [1, 2]
+    |> array.from_list
+    |> array.get(-1)
+}