On PHPMaster.com today there's a new tutorial posted that talks about something that can be a more difficult concept for budding developers to grasp - recursion.

In one of my previous articles I wrote about iterators and how you can use them. Today I’d like to look at the fraternal twin of iteration: recursion. A recursive function is one that calls itself, either directly or in a cycle of function calls. Recursion can also refer to a method of problem solving that first solves a smaller version of the problem and then uses that result plus some other computation to formulate an answer to the original problem.

He starts with an example - one function showing how to calculate a factorial using just looping and the other by having the function call itself. He talks some about the different types of recursion (direct/indirect) and gives a more practical example, a "find in array" function for one with nested subarrays. He also briefly mentions "head" and "tail" recursion, the difference being if it waits for a return value or not. He also offers some general advice when it comes to using recursion and how you have to watch for optimization issues.