Array fold_right

4 files changed, 29 insertions, 1 deletions

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 07d70c7..2b4892c 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`, and `length` functions.
+  `from_list`, `map`, `fold`, `fold_right`, and `length` functions.
diff --git a/src/ffi.js b/src/ffi.js
index 91a2f73..81362bb 100644
--- a/src/ffi.js
+++ b/src/ffi.js
@@ -13,3 +13,7 @@ export function length(thing) {
 export function reduce(thing, acc, fn) {
   return thing.reduce(fn, acc);
 }
+
+export function reduceRight(thing, acc, fn) {
+  return thing.reduceRight(fn, acc);
+}
diff --git a/src/gleam/javascript/array.gleam b/src/gleam/javascript/array.gleam
index 20d12d1..0895ff1 100644
--- a/src/gleam/javascript/array.gleam
+++ b/src/gleam/javascript/array.gleam
@@ -14,3 +14,6 @@ pub external fn map(Array(a), fn(a) -> b) -> Array(b) =
 
 pub external fn fold(Array(e), a, fn(a, e) -> a) -> a =
   "../../ffi.js" "reduce"
+
+pub external fn fold_right(Array(e), a, fn(a, e) -> a) -> a =
+  "../../ffi.js" "reduceRight"
diff --git a/test/gleam/javascript/array_test.gleam b/test/gleam/javascript/array_test.gleam
index 5bf52db..ccebcc7 100644
--- a/test/gleam/javascript/array_test.gleam
+++ b/test/gleam/javascript/array_test.gleam
@@ -16,6 +16,10 @@ pub fn length_test() {
   assert 0 =
     array.from_list([])
     |> array.length
+
+  assert 2 =
+    array.from_list([1, 2])
+    |> array.length
 }
 
 pub fn map_test() {
@@ -48,3 +52,20 @@ pub fn fold_test() {
     |> array.from_list
     |> array.fold([], fn(a, e) { [e, ..a] })
 }
+
+pub fn fold_right_test() {
+  assert [] =
+    []
+    |> array.from_list
+    |> array.fold_right([], fn(a, e) { [e, ..a] })
+
+  assert [1, 2, 3, 4] =
+    [1, 2, 3, 4]
+    |> array.from_list
+    |> array.fold_right([], fn(a, e) { [e, ..a] })
+
+  assert [4, 3, 2, 1] =
+    [4, 3, 2, 1]
+    |> array.from_list
+    |> array.fold_right([], fn(a, e) { [e, ..a] })
+}