Tail recursive functions are iterative processes and are the functional form of a loop. They are an optimized version of recursive functions, as they allow the function’s stack frame to be reused.

Stacks are data structures which work like a stack of boxes. Each time a function calls itself, it adds another box or stack frame to the stack. When we add too many boxes to our stack, they fall down. In the same way, when a function makes a large number of recursive calls, the stack overflows.

If the last action of a function consists of calling a function (like a tail recursive function), one stack frame would be sufficient for both functions. Using a lesser number of stacks or a lesser number of stack frames will prevent a stack from overflowing.

A Comparison

Let’s look at the evaluation of both a recursive function and a tail recursive function to better understand how they differ.

A Simple Recursive Call

The factorial function we defined in a previous lesson uses a simple recursive call.