Like mathematical functions, Sidef's functions can be recursive, take arguments and return values.
func hello (name) {
say "Hello, #{name}!"
The special __FUNC__ keyword refers to the current function:
func factorial (n) {
if (n > 1) {
return (n * __FUNC__(n - 1))
return 1
say factorial(5) # prints: 120


In Sidef, all functions are first-class objects which can be passed around like any other object. Additionally, all functions (including methods) are lexical closures.
func curry(f, *args1) {
func (*args2) {
f(args1..., args2...)
func add(a, b) {
a + b
var adder = curry(add, 1)
say adder(3) #=> 4

Caching functions

By specifying the cached trait in a function (or method) declaration, Sidef will automatically cache it for you.
func fib(n) is cached {
return n if (n <= 1)
fib(n-1) + fib(n-2)
say fib(100) #=> 354224848179261915075

Optional arguments

The parameters of a function can also be declared with a default value, which provides support for optional arguments.
func hello (name="Sidef") {
say "Hello, #{name}!"
hello() # prints: "Hello, Sidef!"
hello("World") # prints: "Hello, World!"
The default value of a parameter is evaluated only when an argument is not provided for that particular parameter, and it can be any arbitrary expression:
func foo (a = 1.25.sqrt, b = 1/2) {
a + b
say foo() # prints the result of: sqrt(1.25) + 1/2
say foo(21, 21) # prints: 42

Named parameters

This is a very nice feature borrowed from Perl 6 which allows a function to be called with named parameters, giving us the flexibility to put the arguments in no specific order:
func divide(a, b) {
a / b
say divide(b: 5, a: 35) # prints: 7

Variadic functions

A slurpy variable in the form of *name can be used as a function parameter to collect the remaining arguments inside an array:
func f(*args) {
say args #=> [1, 2, 3]
f(1, 2, 3)
Alternatively, by using a named variable in the form of :name, the arguments are collected inside an hash:
func f(:pairs) {
say pairs #=> Hash(a=>1, b=>2)
f(a => 1, b => 2)

Typed parameters

A function can be declared with typed parameters, which are checked at run-time.
func concat(String a, String b) {
a + b
Now, the function can only be called with strings as arguments:
say concat("o", "k") # ok
say concat(1, 2) # runtime error
The typed parameters require a specific type of object, but they do not default to anything when no value is provided. This means that all typed-parameters are mandatory, unless a default value is provided:
func concat(String a="foo", String b="bar") {
a + b
say concat() # prints: "foobar"
say concat("mini") # prints: "minibar"
say concat(1, 2) # this is still a run-time error
Last modified 2yr ago