From 032f840e212f82f9b940fe75cdd4789db9aa2ba2 Mon Sep 17 00:00:00 2001
From: Marcin Puc <marcin.e.puc@gmail.com>
Date: Sun, 14 Mar 2021 20:35:28 +0100
Subject: Add {iterator, list}.last

---
 src/gleam/iterator.gleam       | 17 +++++++++++++++++
 src/gleam/list.gleam           | 17 +++++++++++++++++
 test/gleam/iterator_test.gleam | 10 ++++++++++
 test/gleam/list_test.gleam     |  8 ++++++++
 4 files changed, 52 insertions(+)

diff --git a/src/gleam/iterator.gleam b/src/gleam/iterator.gleam
index fa49b87..499cd92 100644
--- a/src/gleam/iterator.gleam
+++ b/src/gleam/iterator.gleam
@@ -946,3 +946,20 @@ pub fn reduce(
       |> Ok
   }
 }
+
+/// Returns the last element in the given iterator.
+///
+/// Returns `Error(Nil)` if the iterator is empty.
+///
+/// ## Examples
+///
+///    > from_list([]) |> last
+///    Error(Nil)
+///
+///    > range(1, 10) |> last
+///    Ok(9)
+///
+pub fn last(iterator: Iterator(element)) -> Result(element, Nil) {
+  iterator
+  |> reduce(fn(elem, _) { elem })
+}
diff --git a/src/gleam/list.gleam b/src/gleam/list.gleam
index 9f88063..f99b729 100644
--- a/src/gleam/list.gleam
+++ b/src/gleam/list.gleam
@@ -1431,3 +1431,20 @@ pub fn scan(
 ) -> List(b) {
   do_scan(list, initial, [], fun)
 }
+
+/// Returns the last element in the given list.
+///
+/// Returns `Error(Nil)` if the list is empty.
+///
+/// ## Examples
+///
+///    > last([])
+///    Error(Nil)
+///
+///    > last([1, 2, 3, 4, 5])
+///    Ok(5)
+///
+pub fn last(list: List(a)) -> Result(a, Nil) {
+  list
+  |> reduce(fn(elem, _) { elem })
+}
diff --git a/test/gleam/iterator_test.gleam b/test/gleam/iterator_test.gleam
index 492bb1e..84459a2 100644
--- a/test/gleam/iterator_test.gleam
+++ b/test/gleam/iterator_test.gleam
@@ -383,3 +383,13 @@ pub fn reduce_test() {
   |> iterator.reduce(with: fn(x, y) { x + y })
   |> should.equal(Ok(15))
 }
+
+pub fn last_test() {
+  iterator.from_list([])
+  |> iterator.last
+  |> should.equal(Error(Nil))
+
+  iterator.range(1, 10)
+  |> iterator.last
+  |> should.equal(Ok(9))
+}
diff --git a/test/gleam/list_test.gleam b/test/gleam/list_test.gleam
index 572812c..5fe2dd5 100644
--- a/test/gleam/list_test.gleam
+++ b/test/gleam/list_test.gleam
@@ -645,3 +645,11 @@ pub fn scan_test() {
   )
   |> should.equal(["Odd", "OddEven", "OddEvenOdd", "OddEvenOddEven"])
 }
+
+pub fn last_test() {
+  list.last([])
+  |> should.equal(Error(Nil))
+
+  list.last([1, 2, 3, 4, 5])
+  |> should.equal(Ok(5))
+}
-- 
cgit v1.2.3