Option map function

1 files changed, 21 insertions, 0 deletions

diff --git a/src/gleam/option.gleam b/src/gleam/option.gleam
index 663cd1f..46327ed 100644
--- a/src/gleam/option.gleam
+++ b/src/gleam/option.gleam
@@ -85,3 +85,24 @@ pub fn unwrap(option: Option(a), or default: a) -> a {
     None -> default
   }
 }
+
+/// Update a value held within the Some of an Option by calling a given function
+/// on it.
+///
+/// If the option is a None rather than Some the function is not called and the
+/// option stays the same.
+///
+/// ## Examples
+///
+///    > map(over: Some(1), with: fn(x) { x + 1 })
+///    Some(2)
+///
+///    > map(over: None, with: fn(x) { x + 1 })
+///    None
+///
+pub fn map(over option: Option(a), with fun: fn(a) -> b) -> Option(b) {
+  case option {
+    Some(x) -> Some(fun(x))
+    None -> None
+  }
+}