Introduce option type (#4150)

* Introduce option type

* Improve test naming

1 files changed, 20 insertions, 0 deletions

diff --git a/src/prelude/maybe.ts b/src/prelude/maybe.ts
new file mode 100644
index 0000000000..f9ac95c0b5
--- /dev/null
+++ b/src/prelude/maybe.ts
@@ -0,0 +1,20 @@
+export interface Maybe<T> {
+	isJust(): this is Just<T>;
+}
+
+export type Just<T> = Maybe<T> & {
+	get(): T
+};
+
+export function just<T>(value: T): Just<T> {
+	return {
+		isJust: () => true,
+		get: () => value
+	};
+}
+
+export function nothing<T>(): Maybe<T> {
+	return {
+		isJust: () => false,
+	};
+}