From 738b9043a5d16f504cbd1de480e5cecceb12e9dd Mon Sep 17 00:00:00 2001
From: Ignatius Bagus <ignatius.mbs@gmail.com>
Date: Mon, 13 Feb 2023 14:19:44 +0800
Subject: [PATCH 1/3] feat: add `memory` function

---
 src/core/standard/index.ts | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/src/core/standard/index.ts b/src/core/standard/index.ts
index 917de479..1eaf7a1c 100644
--- a/src/core/standard/index.ts
+++ b/src/core/standard/index.ts
@@ -52,6 +52,14 @@ export function inverse<Function extends AnyFunction>(fn: Function) {
 	return (...parameters: Reversed): Returned => fn(...parameters.reverse());
 }
 
+export function memory<T>(initial: T, fn: AnyFunction<[previous: T], void>) {
+	let check = initial;
+	return (updated: T) => {
+		if (identical(check, updated)) return;
+		fn(check), (check = updated);
+	};
+}
+
 /**
  * regexp - implementation of global RegExp constructor with escaped pattern
  * @param pattern passed in the form of string literal

From 5d8e76e9d2e9990d2b5de1498224fa922a387fbf Mon Sep 17 00:00:00 2001
From: Ignatius Bagus <ignatius.mbs@gmail.com>
Date: Wed, 1 Mar 2023 14:45:11 +0800
Subject: [PATCH 2/3] make it an identity function

---
 src/core/standard/index.ts | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/src/core/standard/index.ts b/src/core/standard/index.ts
index c106013d..65e97d10 100644
--- a/src/core/standard/index.ts
+++ b/src/core/standard/index.ts
@@ -53,10 +53,12 @@ export function inverse<Function extends AnyFunction>(fn: Function) {
 }
 
 export function memory<T>(initial: T, fn: AnyFunction<[previous: T], void>) {
-	let check = initial;
+	let previous = initial;
 	return (updated: T) => {
-		if (identical(check, updated)) return;
-		fn(check), (check = updated);
+		if (!identical(previous, updated)) {
+			fn(previous), (previous = updated);
+		}
+		return updated;
 	};
 }
 

From edf9b0b3da824a26afe389c757b156c72f812b88 Mon Sep 17 00:00:00 2001
From: Ignatius Bagus <ignatius.mbs@gmail.com>
Date: Wed, 1 Mar 2023 14:49:54 +0800
Subject: [PATCH 3/3] update changelog and docs

---
 CHANGELOG.md       | 1 +
 src/core/README.md | 8 ++++++++
 2 files changed, 9 insertions(+)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 1c2f9129..480d0f8c 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -3,6 +3,7 @@
 ## Unreleased
 
 - ([#211](https://github.com/alchemauss/mauss/pull/211)) fix `ntv.keys` and `ntv.entries` always returns `string`
+- ([#207](https://github.com/alchemauss/mauss/pull/207)) add `memory` function
 - ([#205](https://github.com/alchemauss/mauss/pull/205)) add `size` function to `ntv` namespace
 - ([#204](https://github.com/alchemauss/mauss/pull/204)) add `scope` function
 - ([#202](https://github.com/alchemauss/mauss/pull/202)) add `create` function to `ntv` namespace
diff --git a/src/core/README.md b/src/core/README.md
index 0ae77dbb..708538a0 100644
--- a/src/core/README.md
+++ b/src/core/README.md
@@ -157,6 +157,14 @@ A function to check for values equality between two variables. This will work fo
 
 A function that accepts a function and returns the same function with the order of parameters reversed. This can be used in conjunction with `compare` methods to sort the items in ascending values.
 
+## `memory`
+
+```typescript
+export function memory<T>(initial: T, fn: (previous: T) => void): (updated: T) => T;
+```
+
+A higher-order function that runs a callback function only when the `initial`/previous and `updated` are different.
+
 ## `pipe`
 
 A type-safe higher-order function that accepts any number of arguments, it returns a function with the parameters of the first function passed and a return type/value of the last function.