Introduction to XML in Flash
       by senocular

Recursive Functions
Ok, so looping my not always be the best idea. And yeah, sometimes you're going to have complicated XML that will go levels and levels deep. Sometimes you can't help this - but also you don't want to have to make for loops to handle all that. Have no fear; there are other solutions. One is using recursive function calls to handle like data no matter how nested it is within your XML structure.

A recursive function is a function that calls itself. This is, itself, a form of looping. If you call a function that calls itself, then, as it runs, it will call itself - a function which, since its the same function, also calling itself... which calls itself and so on and so forth until something prevents the function from calling itself again and all the previous function calls resolve. Its just one big function loop. For example, Math.pow, the function that raises a number to a specific power can be written as a recursive function:

Math.pow = function(num, power){

return (power > 0) ? num*Math.pow(num, power-1) : 1;

}

Math.pow, in this execution, checks to see if pow is greater than 0. If so, it returns the passed number times itself to the power of the power passed minus 1 (by calling itself). Effectively, what this does is counts power down until its 0 returning that many multiplications of the num argument times itself - one for each call of Math.pow. In the end you have num to the power-th power.

Recursive functions help you deal with problems that are compounding or require like actions to be performed repeatedly during a single operation - much like looping. However, unlike looping, the nesting of recursive functions is automatic since each function call already contains another call to itself. This provides for a theoretically infinite number of nested calls, though, in Flash, you're limited to using only 256. Loops only become as nested when you write them out to be. That flexibility and scalability is what make recursive functions useful.

When dealing with XML recursion can be helpful if you are unsure how deep your XML may go - how many levels of children does each element have? Though often you will (should) know exactly how your XML is structured, sometimes you won't. An example would be a dump of all the files and folders (and the files and folders within each folders) that are within a certain directory of choice. This directory could be completely empty or it could have folders upon folders of files and other folders. You really don't know. Using a recursive function to list out each folder's contents would work really well since once you've reached another folder, you just call the function again to list out it's contents, repeating the process until all subdirectories have been listed.