Function & Function Calls

Defining new functions is easy, since functions are values, and you can simply assign them to a local or a global variable :

var foo = function() {
	return 0;

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 accept this number of arguments will raise an exception.

You can know the number of arguments needed by a function by using the builtin $nargs. A function that accepts a variable number of arguments returns -1 when used with $nargs. Please also note that builtins can be used as values :

$print($nargs(function(a,b) { return a + b; }); // prints 2
$print($nargs($print)); // prints -1
$print($nargs(0)); // exception

There is one other way of calling a function : builtin $call takes an array of arguments and an object context (see Objects section) as parameters. This builtin can be useful for introspection :

// call the foo function with null context
// and two parameters 3 and 4

Functional languages require partial application (aka currying) : the ability to creates closures by setting a fixed number of arguments of a function, leaving the rest for a later call. The builtin $closure enable to create a closure :

var add = function(x,y) { return x + y };
var plus5 = $closure(add,null,5); // null context and 5 as first argument
$print( plus5(2) ); // 7

The builtin $closure can also be used to fix the this context of a function :

var f = function() { $print(this) };
f = $closure(f,55);
f(); // prints 55

Some languages might want more security about the types of the arguments that are passed to a function, or selecting at runtime different implementations of a function depending on the type of the arguments. There are many ways of doing that in Neko. For example, you might want to add argument checks at the beginning of the function body using runtime type information (RTTI) builtins.

Another useful builtin is $apply which is identical to a direct function call except that if the function requires extra arguments, then its call is delayed until further arguments are used :

var f = function(x,y) { return x + y };
$apply(f,1)(2); // equivalent
$apply(f,1,2); // equivalent

© 2019 Haxe Foundation | Contribute to this page