Throw the cat among the pigeons

[Paul Moore]

On Sunday, 3 May 2015 16:23:59 UTC+1, Cecil Westerhof  wrote:
> > By the way: I think that even if the recursion does not go further
> > as 500, it is still a good idea to use tail recursion. Why use stack
> > space when it is not necessary?
> 
> I pushed the example to GitHub:
>     https://github.com/CecilWesterhof/PythonLibrary/blob/master/mathDecebal.py

You already know this, as your code shows, but tail call recursion elimination is only possible when you have a *direct* tail call (one with the result of the tail call returned immediately to the caller). Even the standard trivial factorial example doesn't have a direct tail call, without rewriting to use an accumulator variable. Which is a non-intuitive transformation to anyone who's not familiar with recursive functional languages and their idioms.

If you're rewriting your recursive function *anyway*, it's not that much harder in many (most?) cases to rewrite it iteratively.

An example of a function that naturally uses direct tail call recursion, but which doesn't have a simple iterative rewrite, would be more compelling. Not particularly compelling (to me, anyway) even so, but still better than factorial or fibonnaci examples.

Paul