From 4895420ff3300c84f5fe3ec3b97aab7a64710092 Mon Sep 17 00:00:00 2001
From: Xie Yuheng <xyheme@gmail.com>
Date: Mon, 24 Jun 2024 06:33:06 +0800
Subject: [PATCH] monads/nothing-monad

---
 TODO.md                     | 1 -
 src/monads/nothing-monad.ts | 7 +++++++
 src/utils/isFunction.ts     | 3 +++
 3 files changed, 10 insertions(+), 1 deletion(-)
 create mode 100644 src/monads/nothing-monad.ts
 create mode 100644 src/utils/isFunction.ts

diff --git a/TODO.md b/TODO.md
index 6a93fd5..dc51c32 100644
--- a/TODO.md
+++ b/TODO.md
@@ -1,4 +1,3 @@
-monads/nothing-monad
 用 generic 函数定义 lift -- 删除 `skipIncompleteInputs`
 monads/supported-monad -- 删除 `maybeUnwrapSupported`
 
diff --git a/src/monads/nothing-monad.ts b/src/monads/nothing-monad.ts
new file mode 100644
index 0000000..42415fd
--- /dev/null
+++ b/src/monads/nothing-monad.ts
@@ -0,0 +1,7 @@
+import { isNothing, nothing } from "../cell/Nothing.js"
+import { defineHandler } from "../generic/index.js"
+import { fmap, join } from "../monad/index.js"
+import { isFunction } from "../utils/isFunction.js"
+
+defineHandler(fmap, [isFunction, isNothing], (f, mx) => nothing)
+defineHandler(join, [isNothing], (mmx) => nothing)
diff --git a/src/utils/isFunction.ts b/src/utils/isFunction.ts
new file mode 100644
index 0000000..c9fcf05
--- /dev/null
+++ b/src/utils/isFunction.ts
@@ -0,0 +1,3 @@
+export function isFunction(x: any): x is Function {
+  return typeof x === "function"
+}