Add iterator.{empty, once, single}

2 files changed, 52 insertions, 0 deletions

diff --git a/src/gleam/iterator.gleam b/src/gleam/iterator.gleam
index 0b747df..c09901c 100644
--- a/src/gleam/iterator.gleam
+++ b/src/gleam/iterator.gleam
@@ -965,3 +965,37 @@ pub fn last(iterator: Iterator(element)) -> Result(element, Nil) {
   iterator
   |> reduce(fn(elem, _) { elem })
 }
+
+/// Creates an iterator that yields no elements.
+///
+/// ## Examples
+///
+///    > empty() |> to_list
+///    []
+///
+pub fn empty() -> Iterator(element) {
+  Iterator(stop)
+}
+
+/// Creates an iterator that yields exactly one element provided by calling the given function.
+///
+/// ## Examples
+///
+///    > once(fn() { 1 }) |> to_list
+///    [1]
+///
+pub fn once(f: fn() -> element) -> Iterator(element) {
+  fn() { Continue(f(), stop) }
+  |> Iterator
+}
+
+/// Creates an iterator that yields the given element exactly once.
+///
+/// ## Examples
+///
+///    > single(1) |> to_list
+///    [1]
+///
+pub fn single(elem: element) -> Iterator(element) {
+  once(fn() { elem })
+}
diff --git a/test/gleam/iterator_test.gleam b/test/gleam/iterator_test.gleam
index 84459a2..53da3db 100644
--- a/test/gleam/iterator_test.gleam
+++ b/test/gleam/iterator_test.gleam
@@ -393,3 +393,21 @@ pub fn last_test() {
   |> iterator.last
   |> should.equal(Ok(9))
 }
+
+pub fn empty_test() {
+  iterator.empty()
+  |> iterator.to_list
+  |> should.equal([])
+}
+
+pub fn once_test() {
+  iterator.once(fn() { 1 })
+  |> iterator.to_list
+  |> should.equal([1])
+}
+
+pub fn single_test() {
+  iterator.single(1)
+  |> iterator.to_list
+  |> should.equal([1])
+}