Make list.range tail recursive

2 files changed, 10 insertions, 3 deletions

diff --git a/src/gleam/list.gleam b/src/gleam/list.gleam
index c787935..1a9d5ce 100644
--- a/src/gleam/list.gleam
+++ b/src/gleam/list.gleam
@@ -1048,10 +1048,14 @@ pub fn sort(list: List(a), by compare: fn(a, a) -> Order) -> List(a) {
 /// ```
 ///
 pub fn range(from start: Int, to stop: Int) -> List(Int) {
+  tail_recursive_range(start, stop, [])
+}
+
+fn tail_recursive_range(start: Int, stop: Int, acc: List(Int)) -> List(Int) {
   case int.compare(start, stop) {
-    order.Eq -> []
-    order.Gt -> [start, ..range(start - 1, stop)]
-    order.Lt -> [start, ..range(start + 1, stop)]
+    order.Eq -> reverse(acc)
+    order.Gt -> tail_recursive_range(start - 1, stop, [start, ..acc])
+    order.Lt -> tail_recursive_range(start + 1, stop, [start, ..acc])
   }
 }
 
diff --git a/test/gleam/list_test.gleam b/test/gleam/list_test.gleam
index 971a5f1..566aa94 100644
--- a/test/gleam/list_test.gleam
+++ b/test/gleam/list_test.gleam
@@ -488,6 +488,9 @@ pub fn range_test() {
 
   list.range(1, -5)
   |> should.equal([1, 0, -1, -2, -3, -4])
+
+  // This should not overflow the stack
+  list.range(1, 100_000)
 }
 
 pub fn repeat_test() {