Add iterator.zip

2 files changed, 37 insertions, 0 deletions

diff --git a/src/gleam/iterator.gleam b/src/gleam/iterator.gleam
index 9146833..010d82a 100644
--- a/src/gleam/iterator.gleam
+++ b/src/gleam/iterator.gleam
@@ -534,3 +534,33 @@ pub fn iterate(
 ) -> Iterator(element) {
   unfold(initial, fn(element) { Next(element, f(element)) })
 }
+
+fn do_zip(
+  left: fn() -> Action(a),
+  right: fn() -> Action(b),
+) -> fn() -> Action(tuple(a, b)) {
+  fn() {
+    case left() {
+      Stop -> Stop
+      Continue(el_left, next_left) ->
+        case right() {
+          Stop -> Stop
+          Continue(el_right, next_right) ->
+            Continue(tuple(el_left, el_right), do_zip(next_left, next_right))
+        }
+    }
+  }
+}
+
+/// Zips two iterators together, emitting values from both
+/// until the shorter one runs out.
+///
+/// ## Examples
+///
+///    > from_list(["a", "b", "c"]) |> zip(range(20, 30)) |> to_list
+///    [tuple("a", 20), tuple("b", 21), tuple("c", 22)]
+///
+pub fn zip(left: Iterator(a), right: Iterator(b)) -> Iterator(tuple(a, b)) {
+  do_zip(left.continuation, right.continuation)
+  |> Iterator
+}
diff --git a/test/gleam/iterator_test.gleam b/test/gleam/iterator_test.gleam
index 098b1b9..ffe57e4 100644
--- a/test/gleam/iterator_test.gleam
+++ b/test/gleam/iterator_test.gleam
@@ -264,3 +264,10 @@ pub fn iterate_test() {
   |> iterator.take(5)
   |> should.equal([1, 3, 9, 27, 81])
 }
+
+pub fn zip_test() {
+  iterator.from_list(["a", "b", "c"])
+  |> iterator.zip(iterator.range(20, 30))
+  |> iterator.to_list
+  |> should.equal([tuple("a", 20), tuple("b", 21), tuple("c", 22)])
+}