feat: Add monoid and monad for Promise

src/promise.ts

@@ -0,0 +1,23 @@
+import type { Monad1 } from "./type-class/monad";
+import type { Monoid } from "./type-class/monoid";
+
+declare const promiseNominal: unique symbol;
+export type PromiseHktKey = typeof promiseNominal;
+
+declare module "./hkt" {
+    interface HktDictA1<A1> {
+        [promiseNominal]: Promise<A1>;
+    }
+}
+
+export const monoid = <T>(identity: T): Monoid<Promise<T>> => ({
+    combine: (l, r) => l.then(() => r),
+    identity: Promise.resolve(identity),
+});
+
+export const monad: Monad1<PromiseHktKey> = {
+    pure: Promise.resolve,
+    map: (f) => (t) => t.then(f),
+    flatMap: (f) => (t) => t.then(f),
+    apply: (f) => (t) => t.then((value) => f.then((func) => func(value))),
+};