Add option.all

Author: sporto

CHANGELOG.md

@@ -3,7 +3,7 @@
 ## Unreleased
 
 - The `list` module gains the `flat_map` function.
-- The `option` module gains the `values` function.
+- The `option` module gains the `all` and `values` functions.
 - The `result` module gains the `values` function.
 - All modules now use the new `#(a, b, ...)` tuple syntax.
 

src/gleam/option.gleam

@@ -11,6 +11,33 @@ pub type Option(a) {
   None
 }
 
+/// Combines a list of options into a single option.
+/// If all elements in the list are Some then returns a Some holding the list of values.
+/// If any element is None then returns None.
+///
+/// ## Examples
+///
+/// ```
+///    > all([Some(1), Some(2)])
+///    Some([1, 2])
+///
+///    > all([Some(1), None])
+///    None
+/// ```
+///
+pub fn all(list: List(Option(a))) -> Option(List(a)) {
+  list.fold_right(
+    list,
+    from: Some([]),
+    with: fn(item, acc) {
+      case acc, item {
+        Some(values), Some(value) -> Some([value, ..values])
+        _, _ -> None
+      }
+    },
+  )
+}
+
 /// Checks whether the option is a Some value.
 ///
 /// ## Examples

test/gleam/option_test.gleam

@@ -1,6 +1,14 @@
 import gleam/should
 import gleam/option.{None, Some}
 
+pub fn all_test() {
+  option.all([Some(1), Some(2), Some(3)])
+  |> should.equal(Some([1, 2, 3]))
+
+  option.all([Some(1), None, Some(3)])
+  |> should.equal(None)
+}
+
 pub fn is_some_test() {
   option.is_some(Some(1))
   |> should.be_true