From 4942ac97ff67c97c0673b8131244e78ae35a341e Mon Sep 17 00:00:00 2001
From: Louis Pilfold <louis@lpil.uk>
Date: Thu, 13 Jul 2023 14:38:46 +0100
Subject: Add deprecated version

---
 CHANGELOG.md         | 3 ++-
 src/gleam/list.gleam | 6 ++++++
 2 files changed, 8 insertions(+), 1 deletion(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 18f9c04..6213b65 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -3,7 +3,8 @@
 ## Unreleased
 
 - The `list` module gains the `list.map2` function.
-- `flatten` has been renamed to `concat` in the `list` module.
+- `flatten` has been renamed to `concat` in the `list` module. The old name is
+  still available as an alias and is deprecated.
 
 ## v0.29.2 - 2023-06-21
 
diff --git a/src/gleam/list.gleam b/src/gleam/list.gleam
index ed1d718..75a66ef 100644
--- a/src/gleam/list.gleam
+++ b/src/gleam/list.gleam
@@ -683,6 +683,12 @@ pub fn concat(lists: List(List(a))) -> List(a) {
   do_concat(lists, [])
 }
 
+// TODO: Add deprecation attribute and then remove later.
+/// This function is deprecated, see `concat` instead.
+pub fn flatten(lists: List(List(a))) -> List(a) {
+  do_concat(lists, [])
+}
+
 /// Maps the list with the given function into a list of lists, and then flattens it.
 ///
 /// ## Examples
-- 
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