In chapter 2 of OCaml from the very beginning, I learned the following:

### Naming an expression

- Use the following constructs to define our own
**name**(e.g.,**x**) to stand for the result of evaluating an expression:**let x =**(expression) ;;**let x =**(expression)**in**(another expression) ;;

- OCaml replies to confirm that an expression x is named, and confirm its type and value. E.g., let x = 200 ;; :

* val x : int = 200*

### Naming a function

- Use the following construct to define a
**function**(e.g.**cube**) that takes an**argument**(e.g.**x**), and applies it to the function as defined:**let cube x =**x * x * x ;;

- OCaml replies to confirm that a function cube is named, and confirm the type of the argument(s) it takes, and the type of the value the function evaluates to:

* val cube : int -> int : <fun>*

### Naming a recursive function

- A
**recursive function**is a function which uses itself. That is, when we define such a function, its own function name has to be in the function definition. - Use the following construct to define a recursive function (e.g.
**factorial**) that takes an argument, and applies it to the function as defined:- let
**rec factorial**x =

if x = 1 then 1 else factorial (x – 1) * x ;;

- let
- OCaml replies similarly to when a function is defined, telling us the types of the argument(s) and the value the function evaluates to:

* val factorial : int -> int = <fun>*

- Make sure that any recursive function you define
**terminates**. Check that you have given the recursive function a way to terminate in all cases of the appropriate type of the argument(s). - OCaml has a built-in function named
**not**. not takes an argument of type bool and returns a value of type bool. That is, when you type ‘not’ in OCaml, it replies with:

* – : bool -> bool = <fun>*