From 46ed11c1de1d9cf657d0bbc3ef4ddcc11be5d51a Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Alexander=20W=C3=BChr?= <alex@pnyhf.eu>
Date: Fri, 13 Sep 2024 09:45:32 +0200
Subject: [PATCH] feat(iterator): implement `iterator_window_by_2` (closes #2)

---
 src/brilo.gleam       | 20 ++++++++++++++++++++
 test/brilo_test.gleam | 35 +++++++++++++++++++++++++++++++++--
 2 files changed, 53 insertions(+), 2 deletions(-)

diff --git a/src/brilo.gleam b/src/brilo.gleam
index 5aa0616..233265a 100644
--- a/src/brilo.gleam
+++ b/src/brilo.gleam
@@ -51,3 +51,23 @@ pub fn iterator_window(i: Iterator(a), by n: Int) -> Iterator(Iterator(a)) {
 
   iterator.unfold(from: i, with: yield)
 }
+
+/// Returns an iterator of tuples containing two contiguous elements.
+///
+/// ## Examples
+///
+/// ```gleam
+/// iterator_window_by_2([1,2,3,4])
+///   |> iterator.to_list
+/// // -> [#(1, 2), #(2, 3), #(3, 4)]
+/// ```
+///
+/// ```gleam
+/// iterator_window_by_2([1])
+///   |> iterator.to_list
+/// // -> []
+/// ```
+///
+pub fn iterator_window_by_2(i: Iterator(a)) -> Iterator(#(a, a)) {
+  iterator.zip(i, iterator.drop(i, 1))
+}
diff --git a/test/brilo_test.gleam b/test/brilo_test.gleam
index 4604980..ae9fb40 100644
--- a/test/brilo_test.gleam
+++ b/test/brilo_test.gleam
@@ -19,12 +19,12 @@ pub fn iterator_from_string_test() {
 }
 
 pub fn iterator_window_test() {
-  [1, 2, 3]
+  [1, 2, 3, 4, 5]
   |> iterator.from_list
   |> brilo.iterator_window(2)
   |> iterator.map(iterator.to_list)
   |> iterator.to_list
-  |> should.equal([[1, 2], [2, 3]])
+  |> should.equal([[1, 2], [2, 3], [3, 4], [4, 5]])
 }
 
 pub fn iterator_window_empty_test() {
@@ -61,3 +61,34 @@ pub fn iterator_window_over_size_test() {
   |> iterator.to_list
   |> should.equal([])
 }
+
+pub fn iterator_window_by_2_test() {
+  [1, 2, 3, 4, 5]
+  |> iterator.from_list
+  |> brilo.iterator_window_by_2
+  |> iterator.to_list
+  |> should.equal([#(1, 2), #(2, 3), #(3, 4), #(4, 5)])
+}
+
+pub fn iterator_window_by_2_empty_test() {
+  iterator.empty()
+  |> brilo.iterator_window_by_2
+  |> iterator.to_list
+  |> should.equal([])
+}
+
+pub fn iterator_window_by_2_full_size_test() {
+  [1, 2]
+  |> iterator.from_list
+  |> brilo.iterator_window_by_2
+  |> iterator.to_list
+  |> should.equal([#(1, 2)])
+}
+
+pub fn iterator_window_by_2_over_size_test() {
+  [1]
+  |> iterator.from_list
+  |> brilo.iterator_window_by_2
+  |> iterator.to_list
+  |> should.equal([])
+}