Add gleam/set.{map}.

2 files changed, 22 insertions, 0 deletions

diff --git a/src/gleam/set.gleam b/src/gleam/set.gleam
index 12bfba1..9e64b07 100644
--- a/src/gleam/set.gleam
+++ b/src/gleam/set.gleam
@@ -218,6 +218,21 @@ pub fn filter(
   Set(dict.filter(in: set.dict, keeping: fn(m, _) { predicate(m) }))
 }
 
+/// Creates a new set from a given set with the result of applying the given
+/// function to each member.
+///
+/// ## Examples
+///
+/// ```gleam
+/// map(from_list([1, 2, 3, 4], fn(x) { x * 2 }))
+/// // -> [2, 4, 6, 8]
+/// ```
+pub fn map(set: Set(member), with fun: fn(member) -> mapped) -> Set(mapped) {
+  fold(over: set, from: new(), with: fn(acc, member) {
+    insert(acc, fun(member))
+  })
+}
+
 /// Creates a new set from a given set with all the same entries except any
 /// entry found on the given list.
 ///
diff --git a/test/gleam/set_test.gleam b/test/gleam/set_test.gleam
index 908fe29..46d4d13 100644
--- a/test/gleam/set_test.gleam
+++ b/test/gleam/set_test.gleam
@@ -83,6 +83,13 @@ pub fn fold_test() {
   |> should.equal(13)
 }
 
+pub fn map_test() {
+  [1, 2, 3, 4]
+  |> set.from_list
+  |> set.map(with: fn(x) { x * 2 })
+  |> should.equal(set.from_list([2, 4, 6, 8]))
+}
+
 pub fn filter_test() {
   [1, 4, 6, 3, 675, 44, 67]
   |> set.from_list()