# Function

## Function

Functions are first class objects like Int or String and can be stored in local variables (even in Lists or Maps), passed as function parameters or returned by a function. Functions can be implemented in Gravity or in a native language with calling conventions compatible with ANSI C.

Functions are called by value. This means that foo(1) calls the function which is the value of the variable foo. Calling a value that is not a function (or does not implement the exec method) will raise a runtime error.

``````    func main() {
var a = 10;
var b = 20;
return a + b;
}``````
``````    func f1() {
return 10;
}

func f2() {
return f1;
}

func main() {
// a is now function f2
var a = f2;

// b is now the return value of f2 which is function f1
var b = a();

// return value is f1() which is 10
return b();

// above code is equivalent to
return f2()();
}``````

### Function parameters

Functions aren’t very useful if you can’t pass values to them so you can provide a parameter list in the function declaration. Gravity performs no check on the number of parameters so you can call a function providing more or less parameters.

``````    func sum(a, b) {
return a + b;
}

// execute the sum function
// and returns 30 as result
sum(10,20);``````

If a function is called with missing arguments (less than declared), the missing values are set to undefined.

``````    // sum modified to take in account missing arguments
func sum(a, b) {
// equivalent to if (a == undefined) a = 30;
if (!a) a = 30;

// equivalent to if (b == undefined) b = 50;
if (!b) b = 50;

return a + b;
}

// execute the sum function without any argument
// a has a 30 default value and b has a 50 default value
// return value is 80
sum();``````

If a function is called with more arguments (more than declared), the additional arguments can be accessed using the _args array.

``````    // sum modified to accept a variable number of arguments
func sum() {
var tot = 0;
for (var i in 0..<_args.count) {
tot += _args[i];
}
}

// execute the sum function with a variable number
// of arguments returns 550 as result
sum(10,20,30,40,50,60,70,80,90,100);``````

### Recursion

Function recursion is fully supported in Gravity (current function can be accessed using the _func reserved keyword):

``````    func fibonacci (n) {
if (n<2) return n;
// could be written as return _func(n-2) + _func(n-1)
return fibonacci(n-2) + fibonacci(n-1);
}

func main() {
return fibonacci(20);
}``````

### Returning values

A function without a return statement returns null by default. You can explicitly return a value using a return statement.