diff --git a/TODO.md b/TODO.md
index d328984..6a93fd5 100644
--- a/TODO.md
+++ b/TODO.md
@@ -1,9 +1,11 @@
+monads/nothing-monad
+用 generic 函数定义 lift -- 删除 `skipIncompleteInputs`
+monads/supported-monad -- 删除 `maybeUnwrapSupported`
+
 > propagator 支持 dependencies for provenance
 >
 > - https://github.com/cicada-lang/propagator/issues/2
 
-fix `maybeUnwrapSupported` -- learn from `nary-unpacking`
-
 `barometer` -- 的测试带上 `promises` -- 用论文中讲故事的方式来写测试
 
 fix `isContradiction` for `Supported`
diff --git a/src/monad/index.ts b/src/monad/index.ts
new file mode 100644
index 0000000..52927c5
--- /dev/null
+++ b/src/monad/index.ts
@@ -0,0 +1,5 @@
+import { defineGeneric } from "../generic/index.js"
+
+export const fmap = defineGeneric({ default: (f, mx) => f(mx) })
+export const join = defineGeneric({ default: (mmx) => mmx })
+export const bind = (mx: any, f: (x: any) => any) => join(fmap(f, mx))