> For the complete documentation index, see [llms.txt](https://smllang.gitbook.io/home/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://smllang.gitbook.io/home/basics/functions.md).

# Functions

What function does that function, function?

### Functions

SMLL is said to be a functional programming language, that is to say, functions are first-class citizens in this language. Functions can be created, called, stored, passed to functions and returned from other functions. In this section I am just going to introduce the basic usage and creation of functions in SMLL. 

{% hint style="info" %}
In SMLL all functions have a return type and must always return a value, even unit is a value.
{% endhint %}

{% code lineNumbers="true" %}

```sml
fn main(): Unit => {
    val sum = add(20, 50)
    val result  = "20 + 50 is = " + sum
    display(result)     
    ()
}

fn add(x: Int, y: Int): Int => x + y
fn display(answer: String): Unit => println(name)
```

{% endcode %}

Functions are declared with the fun keyword, followed by a name, arguments and the return type. Then an arrow operator is expected, separating the function header with the body. After the array is a single expression. SMLL functions execute a single expression, even blocks are expressions and blocks can contain more than 1 expressions such that the last one is the return value. Similar to standard compiled programming languages, the entry point of the program is main and functions can be declared anywhere.