Add the Option type.

2 files changed, 56 insertions, 0 deletions

diff --git a/src/gleam/option.gleam b/src/gleam/option.gleam
new file mode 100644
index 0000000..30bc1e2
--- /dev/null
+++ b/src/gleam/option.gleam
@@ -0,0 +1,38 @@
+/// Option represents a value that may be present or not. Some means the value is
+/// present, None means the value is not.
+///
+/// This is Gleam's alternative to having a value that could be Null, as is
+/// possible in some other languages.
+///
+pub type Option(a) {
+  Some(a)
+  None
+}
+
+/// Check whether the option is a Some value.
+///
+/// ## Examples
+///
+///    > is_some(Some(1))
+///    True
+///
+///    > is_some(None)
+///    False
+///
+pub fn is_some(option: Option(a)) -> Bool {
+  option != None
+}
+
+/// Check whether the option is a None value.
+///
+/// ## Examples
+///
+///    > is_none(Some(1))
+///    False
+///
+///    > is_none(None)
+///    True
+///
+pub fn is_none(option: Option(a)) -> Bool {
+  option == None
+}
diff --git a/test/gleam/option_test.gleam b/test/gleam/option_test.gleam
new file mode 100644
index 0000000..2361e32
--- /dev/null
+++ b/test/gleam/option_test.gleam
@@ -0,0 +1,18 @@
+import gleam/should
+import gleam/option.{Some, None}
+
+pub fn is_some_test() {
+  option.is_some(Some(1))
+  |> should.be_true
+
+  option.is_some(None)
+  |> should.be_false
+}
+
+pub fn is_none() {
+  option.is_none(Some(1))
+  |> should.be_false
+
+  option.is_none(None)
+  |> should.be_true
+}