docs: update atom.mdx

docs/core/atom.mdx

@@ -38,6 +38,10 @@ const writeOnlyAtom = atom(
   (get, set, update) => {
     // `update` is any single value we receive for updating this atom
     set(priceAtom, get(priceAtom) - update.discount)
+    // or we can pass a function as the second parameter
+    // the function will be invoked,
+    //  receiving the atom's current value as its first parameter
+    set(priceAtom, (price) => price - update.discount)
   },
 )
 const readWriteAtom = atom(
@@ -79,24 +83,24 @@ const Component = ({ value }) => {
 function atom<Value>(initialValue: Value): PrimitiveAtom<Value>
 
 // read-only atom
-function atom<Value>(read: (get: Getter) => Value | Promise<Value>): Atom<Value>
+function atom<Value>(read: (get: Getter) => Value): Atom<Value>
 
 // writable derived atom
-function atom<Value, Update>(
-  read: (get: Getter) => Value | Promise<Value>,
-  write: (get: Getter, set: Setter, update: Update) => void | Promise<void>,
-): WritableAtom<Value, Update>
+function atom<Value, Args extends unknown[], Result>(
+  read: (get: Getter) => Value,
+  write: (get: Getter, set: Setter, ...args: Args) => Result,
+): WritableAtom<Value, Args, Result>
 
 // write-only derived atom
-function atom<Value, Update>(
+function atom<Value, Args extends unknown[], Result>(
   read: Value,
-  write: (get: Getter, set: Setter, update: Update) => void | Promise<void>,
-): WritableAtom<Value, Update>
+  write: (get: Getter, set: Setter, ...args: Args) => Result,
+): WritableAtom<Value, Args, Result>
 ```
 
 - `initialValue`: the initial value that the atom will return until its value is changed.
-- `read`: a function that's called on every re-render. The signature of `read` is `(get) => Value | Promise<Value>`, and `get` is a function that takes an atom config and returns its value stored in Provider as described below. Dependency is tracked, so if `get` is used for an atom at least once, the `read` will be reevaluated whenever the atom value is changed.
-- `write`: a function mostly used for mutating atom's values, for a better description; it gets called whenever we call the second value of the returned pair of `useAtom`, the `useAtom()[1]`. The default value of this function in the primitive atom will change the value of that atom. The signature of `write` is `(get, set, update) => void | Promise<void>`. `get` is similar to the one described above, but it doesn't track the dependency. `set` is a function that takes an atom config and a new value which then updates the atom value in Provider. `update` is an arbitrary value that we receive from the updating function returned by `useAtom` described below.
+- `read`: a function that's evaluated whenever the atom is read. The signature of `read` is `(get) => Value`, and `get` is a function that takes an atom config and returns its value stored in Provider as described below. Dependency is tracked, so if `get` is used for an atom at least once, the `read` will be reevaluated whenever the atom value is changed.
+- `write`: a function mostly used for mutating atom's values, for a better description; it gets called whenever we call the second value of the returned pair of `useAtom`, the `useAtom()[1]`. The default value of this function in the primitive atom will change the value of that atom. The signature of `write` is `(get, set, ...args) => Result`. `get` is similar to the one described above, but it doesn't track the dependency. `set` is a function that takes an atom config and a new value which then updates the atom value in Provider. `...args` is the arguments that we receive when we call `useAtom()[1]`. `Result` is the return value of the `write` function.
 
 ```js
 const primitiveAtom = atom(initialValue)
@@ -117,7 +121,10 @@ Note: While, the debug labels don’t have to be unique, it’s generally recomm
 
 The created atom config can have an optional property `onMount`. `onMount` is a function which takes a function `setAtom` and returns `onUnmount` function optionally.
 
-The `onMount` function is called when the atom is first used in a provider, and `onUnmount` is called when it’s no longer used. In some edge cases, an atom can be unmounted and then mounted immediately.
+The `onMount` function is called when the atom is subscribed in the provider in the first time,
+and `onUnmount` is called when it’s no longer subscribed.
+In some cases (like [React strict mode](https://react.dev/reference/react/StrictMode)),
+an atom can be unmounted and then mounted immediately.
 
 ```js
 const anAtom = atom(1)
@@ -126,6 +133,20 @@ anAtom.onMount = (setAtom) => {
   setAtom(c => c + 1) // increment count on mount
   return () => { ... } // return optional onUnmount function
 }
+
+const Component = () => {
+  // `onMount` will be called when the component is mounted in the following cases:
+  useAtom(anAtom)
+  useAtomValue(anAtom)
+
+  // however, in the following cases,
+  //  `onMount` will not be called because the atom is not subscribed:
+  useSetAtom(anAtom)
+  useAtomCallback(
+    useCallback((get) => get(anAtom), []),
+  )
+  // ...
+}
 ```
 
 Calling `setAtom` function will invoke the atom’s `write`. Customizing `write` allows changing the behavior.