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A function is a self-contained block of code that is defined once and used many times and that performs a specific task. You can give the function a name that identifies what it does and you can use this name to "call" the function to perform its task when needed

Define a function

To define a function it is possible to use the keyword func followed by the name of the function and one or more parameters:

func my_func() {

func hello(name) {
io.print("Hello", name)

In Argon, if a function does not accept any parameters, it is possible to omit the parentheses that normally follow the function name:

func my_func {

If you wish it is also possible to create inline functions using the arrow operator, in this case the function is not associated with any name and should be used immediately or saved in a variable so that it can be used later:

var hello = (name) => {
io.print("Hello", name)

In an inline function it is not possible to omit the parentheses if the function takes no arguments.

At this point you may be wondering how to call a function, in Argon there are two different syntaxes for invoking a function:

  • Call operator ()
  • Pipeline operator |>

The common way is to use the call operator by following the function name with an open and a closed parenthesis. Inside the parentheses, one or more arguments can be passed in the same order as they were defined in the function definition:


hello("John William Strutt") # Output: Hello John William Strutt

The pipeline operator is extremely convenient and elegant for calling several functions in cascade and can be used on functions that take at least one argument. This operator allows you to pass the first parameter of a function outside the parentheses. If the function accepts multiple arguments, the arguments following the first must be passed as usual.

"John William Strutt" |> hello # Output: Hello John William Strutt

N.B. If the function accepts only one argument it is possible to omit the call operator (the round brackets following the function name)

Function parameters

Argon functions are extremely flexible in terms of accepted parameters. It is possible to define functions with zero or more parameters, but also functions that take a variable number of arguments and associative parameters that take arguments of the form key=value.

Function without parameters

Functions that don't take input parameters are the simplest, here's an example of a function that doesn't take input parameters. (Remember: In this case the function name may not be followed by the parentheses):

func hello_world {
return "Hello world!"

hello_world |> io.print

Function with multiple parameters

Functions can have several input parameters, these parameters are written inside the function parentheses separated by a comma:

func hello(name, already_greeted) {
if already_Greeted {
io.print("Hello", name)
} else {
"Hello again," |> io.print(name)

hello("Bob", false)

Function with variadic parameters

It is possible to construct functions that accept an arbitrary number of parameters (an example of this function is io.print) to do this it is sufficient to prepend the symbol ... to the name of the last parameter:

func variadic(...names) {
var name
for name in names {
io.print("Hello", name)

variadic("Alice", "Bob", "Charlie", "Dave", "Eve")

# OR

var names = ["Alice", "Bob", "Charlie", "Dave", "Eve"]


Function with associative parameters

It is possible to construct functions with associative parameters (an example is again the function io.print), to do this you can proceed in two ways:

1) It is possible to create an associative parameter by placing an = after the name of the parameter (with this method you can also define the default value associated with the parameter, as in the example below).

2) It is possible to prepend the symbol & to the name of the last parameter.

func hello(name, start="", &kwargs) {
var end = kwargs?.contains("end") ? kwargs["end"] : "!"

"%sHello %s%s" % (start, name, end) |> io.print

hello("Alice") # Output: Hello Alice!

hello("Alice", start="!", end="$") # Output: !Hello Bob$

NB: &kwargs is a dictionary that contains all the associative arguments passed as arguments to the called function, while postfix parameters with = will contain the value passed as an argument, if any, otherwise the default value.

Mixing together

It is possible to combine the various types of parameter definition together, however it is necessary to respect a precise order: first go the normal parameters (if present), then the parameter that allows transforming the function into a variadic function and finally the associative parameter:

[parameters,] [...args,] [param=[default value],] [&kwargs]

Return value

Argon functions always return nil by default, however it is possible to return any kind of value via the return keyword:

func concat_ns(name, surname) {
return "%s %s" % (name, surname)

concat_ns("Alice", "Rossi") |> io.print

Nested function

All the functions encountered so far are examples of global functions since they are defined in the global scope.

Nested functions are hidden from the outside world, but can be called and used by the functions that nest them. Furthermore, a nested function can be returned by the function that closes it, allowing its use in another scope.

Finally, nested functions enjoy a special property, but we will see it in the chapter dedicated to Closures!

func inc_or_dec(backward) {
return backward ? (number) => {
return number - 1
} : (number) => {
return number + 1

var num = 0

inc_or_dec(false)(num) |> io.print