cycle

2 files changed, 25 insertions, 0 deletions

diff --git a/src/gleam/iterator.gleam b/src/gleam/iterator.gleam
index a2ca7d8..a4c9361 100644
--- a/src/gleam/iterator.gleam
+++ b/src/gleam/iterator.gleam
@@ -160,3 +160,20 @@ pub fn filter(iterator: Iterator(a), for predicate: fn(a) -> Bool) -> Iterator(a
   |> do_filter(_, predicate)
   |> opaque
 }
+
+fn do_cycle(next: fn() -> Action(a), reset: fn() -> Action(a)) {
+  fn() {
+    case next() {
+      Continue(e, iterator) -> Continue(e, do_cycle(iterator, reset))
+      Stop -> do_cycle(reset, reset)()
+    }
+  }
+}
+
+// TODO: document
+pub fn cycle(iterator: Iterator(a)) -> Iterator(a) {
+  let iterator = iterator |> unopaque
+  iterator
+  |> do_cycle(_, iterator)
+  |> opaque
+}
diff --git a/test/gleam/iterator_test.gleam b/test/gleam/iterator_test.gleam
index b587d12..447e912 100644
--- a/test/gleam/iterator_test.gleam
+++ b/test/gleam/iterator_test.gleam
@@ -99,3 +99,11 @@ pub fn repeat_test() {
   |> iterator.take(_, 5)
   |> expect.equal(_, [1, 1, 1, 1, 1])
 }
+
+pub fn cycle_test() {
+  [1, 2, 3]
+  |> iterator.from_list
+  |> iterator.cycle
+  |> iterator.take(_, 9)
+  |> expect.equal(_, [1, 2, 3, 1, 2, 3, 1, 2, 3])
+}