Option flatten function

3 files changed, 35 insertions, 1 deletions

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 8918f8e..48415df 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -15,7 +15,7 @@
 - The `dynamic.tuple2_of` function has been renamed to `dynamic.typed_tuple2`.
 - The `list.traverse` function has been renamed to `list.try_map`.
 - The `list.traverse` first argument gains the label `over`.
-- Added the `map` function to the the `option` module.
+- The `option` module gains the the `map` and `flatten` functions.
 
 ## 0.9.0 - 2020-05-26
 
diff --git a/src/gleam/option.gleam b/src/gleam/option.gleam
index 46327ed..9a2e479 100644
--- a/src/gleam/option.gleam
+++ b/src/gleam/option.gleam
@@ -106,3 +106,23 @@ pub fn map(over option: Option(a), with fun: fn(a) -> b) -> Option(b) {
     None -> None
   }
 }
+
+/// Merge a nested Option into a single layer.
+///
+/// ## Examples
+///
+///    > flatten(Some(Some(1)))
+///    Some(1)
+///
+///    > flatten(Some(None))
+///    None
+///
+///    > flatten(None)
+///    None
+///
+pub fn flatten(option: Option(Option(a))) -> Option(a) {
+  case option {
+    Some(x) -> x
+    None -> None
+  }
+}
diff --git a/test/gleam/option_test.gleam b/test/gleam/option_test.gleam
index edbb569..03f4186 100644
--- a/test/gleam/option_test.gleam
+++ b/test/gleam/option_test.gleam
@@ -54,3 +54,17 @@ pub fn map_option_test() {
   |> option.map(fn(x) { x + 1 })
   |> should.equal(None)
 }
+
+pub fn flatten_option_test() {
+  Some(Some(1))
+  |> option.flatten()
+  |> should.equal(Some(1))
+
+  Some(None)
+  |> option.flatten()
+  |> should.equal(None)
+
+  None
+  |> option.flatten()
+  |> should.equal(None)
+}