range

2 files changed, 43 insertions, 0 deletions

diff --git a/src/gleam/iterator.gleam b/src/gleam/iterator.gleam
index 33ff8d0..690d66e 100644
--- a/src/gleam/iterator.gleam
+++ b/src/gleam/iterator.gleam
@@ -176,3 +176,20 @@ pub fn cycle(iterator: Iterator(a)) -> Iterator(a) {
   |> do_cycle(_, iterator)
   |> opaque
 }
+
+fn do_range(current, limit, inc) -> fn() -> Action(Int) {
+  case current == limit {
+    True -> fn() { Stop }
+    False -> fn() { Continue(current, do_range(current + inc, limit, inc)) }
+  }
+}
+
+// TODO: document
+pub fn range(from start, to stop) -> Iterator(Int) {
+  case start < stop {
+    True -> 1
+    False -> -1
+  }
+  |> do_range(start, stop, _)
+  |> opaque
+}
diff --git a/test/gleam/iterator_test.gleam b/test/gleam/iterator_test.gleam
index fe0a854..079d57d 100644
--- a/test/gleam/iterator_test.gleam
+++ b/test/gleam/iterator_test.gleam
@@ -117,3 +117,29 @@ pub fn unfold_test() {
   |> iterator.take(_, 5)
   |> expect.equal(_, [])
 }
+
+pub fn range_test() {
+  iterator.range(0, 0)
+  |> iterator.to_list
+  |> expect.equal(_, [])
+
+  iterator.range(1, 1)
+  |> iterator.to_list
+  |> expect.equal(_, [])
+
+  iterator.range(-1, -1)
+  |> iterator.to_list
+  |> expect.equal(_, [])
+
+  iterator.range(0, 1)
+  |> iterator.to_list
+  |> expect.equal(_, [0])
+
+  iterator.range(0, 5)
+  |> iterator.to_list
+  |> expect.equal(_, [0, 1, 2, 3, 4])
+
+  iterator.range(1, -5)
+  |> iterator.to_list
+  |> expect.equal(_, [1, 0, -1, -2, -3, -4])
+}