From e9955e01d60773b96017acc1c6cd3dfae4dfb3e6 Mon Sep 17 00:00:00 2001
From: Aya Morisawa <AyaMorisawa4869@gmail.com>
Date: Wed, 6 Feb 2019 13:42:35 +0900
Subject: Introduce option type (#4150)

* Introduce option type

* Improve test naming
---
 src/prelude/maybe.ts | 20 ++++++++++++++++++++
 1 file changed, 20 insertions(+)
 create mode 100644 src/prelude/maybe.ts

(limited to 'src/prelude')

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,
+	};
+}
-- 
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