Add iterator.iterate

2 files changed, 21 insertions, 0 deletions

diff --git a/src/gleam/iterator.gleam b/src/gleam/iterator.gleam
index 9bbf9d0..f441859 100644
--- a/src/gleam/iterator.gleam
+++ b/src/gleam/iterator.gleam
@@ -494,3 +494,17 @@ pub fn find(
     Stop -> Error(Nil)
   }
 }
+
+/// Creates an iterator that inifinitely applies a function to a value.
+///
+/// ## Examples
+///
+///    > iterate(1, fn(n) { n * 3 }) |> take(5)
+///    [1, 3, 9, 27, 81]
+///
+pub fn iterate(
+  from initial: element,
+  with f: fn(element) -> element,
+) -> Iterator(element) {
+  unfold(initial, fn(element) { Next(element, f(element)) })
+}
diff --git a/test/gleam/iterator_test.gleam b/test/gleam/iterator_test.gleam
index 0f836c6..af38508 100644
--- a/test/gleam/iterator_test.gleam
+++ b/test/gleam/iterator_test.gleam
@@ -250,3 +250,10 @@ pub fn find_test() {
   |> iterator.find(fn(cat: Cat) { cat.id == 10 })
   |> should.equal(Ok(Cat(id: 10)))
 }
+
+pub fn iterate_test() {
+  fn(x) { x * 3 }
+  |> iterator.iterate(from: 1)
+  |> iterator.take(5)
+  |> should.equal([1, 3, 9, 27, 81])
+}