Exceptions

Exceptions are often referred to as "nonlocal jumps". It's a very good way for handling errors than can happen at several calls between the function that yield an error and the handler that will take care of it. Raising an exception is done using the $throw builtin, and catching it is done using the try...catch syntax. Please note that any value can be an exception, it's up to you to decide which structure you want to use :

var foo = function() {
	$throw("failure");
}
try
	foo()
catch e {
	$print(e); // prints "failure"
}

Every time an exception is caught, the exception stack is stored and can be retrieved using the builtin $excstack(). It contains the filenames and positions of the different calls between the try and the place the exception was raised.

try
	foo()
catch e {
	$print(e," raised from : ",$excstack());
}

In some cases, you want to filter exceptions and catch only some of them. You then need to catch all the exceptions, check if the exception is filtered, and raise it again if not. However, in order to lose the exception stack by throwing a new exception, you can use the $rethrow builtin which will add the two stacks together (the current one and the one to the next catch).

try
	foo()
catch e {
	if( $typeof(e) == $tint )
		$print("catched !")
	else
		$rethrow(e);
}

Please note that you can rethrow another exception, so it's easier to rewrap some Neko libraries exceptions with your own format.

It is also possible to get the current call stack at any point of a Neko program using the $callstack() builtin.