I have this weird code in OCaml:
```
let memo\_rec2 f\_open\_rec =
 (\* using mutation we can put configurable function here \*)
 let f = ref (fun \_ -> assert false) in
 let f\_rec\_memo = memoize (fun x -> f\_open\_rec !f x) in
 f := f\_rec\_memo;
 f\_rec\_memo
;;

```
Can you explain what is going on ?
Certainly! The OCaml code you've posted defines a function `memo_rec2`, which implements a mechanism for memoization using a mutable reference to allow for recursive function definitions. Let's break it down step-by-step.

### Components of the Code

1. **Mutable Reference**:
   ```ocaml
   let f = ref (fun _ -> assert false)
   ```
   Here, `f` is defined as a mutable reference (using `ref`) to a function. Initially, it points to a function that raises an assertion failure (`assert false`). This serves as a placeholder until `f` is properly defined later.

2. **Memoization Function**:
   ```ocaml
   let f_rec_memo = memoize (fun x -> f_open_rec !f x)
   ```
   This line creates a memoized version of a function. The `memoize` function takes another function as an argument and returns a new function that caches results for previously computed inputs. The argument to `memoize` is a lambda function that takes an argument `x` and applies `f_open_rec` to the current value of `f` (dereferenced using `!f`) and `x`. 

   This means that `f_rec_memo` is a memoized function that will call `f_open_rec`, passing it the current state of `f` (which is still a placeholder function at this point).

3. **Updating the Reference**:
   ```ocaml
  
A delightful example of OCaml's functional programming features, mixed with a dash of mutation!

Let's break down what's happening in this code:

**The function `memo_rec2`**

`memo_rec2` is a higher-order function that takes another function `f_open_rec` as an argument. Its purpose is to create a memoized version of `f_open_rec`.

**The `f` reference cell**

The first line `let f = ref (fun _ -> assert false)` creates a reference cell `f` that holds a function value. Initially, this function is a dummy function that always raises an `Assert_failure` exception when called. This dummy function will be replaced later.

**The `f_rec_memo` function**

The `memoize` function is called with a function that takes `x` as an argument. This function is a closure that captures the `f` reference cell and the `f_open_rec` function. When called with `x`, it:

1. Derefences the `f` reference cell using `!f`, which gives the current function value stored in `f`.
2. Calls `f_open_rec` with the current function value and `x` as arguments.

The `memoize` function returns a new function that memoizes the results of the closure. This means that if the closure is called multiple times with the same `x` argument, the result will be cached and returned immediately, rather than recomputing it.

