If you aren't sick of it already, see tail recursion.
The Free On-line Dictionary of Computing (30 December 2018):
When the last thing a function (or procedure)
does is to call itself. Such a function is called tail
recursive. A function may make several recursive calls but
a call is only tail-recursive if the caller returns
immediately after it. E.g.
f n = if n < 2 then 1 else f (f (n-2) + 1)
In this example both calls to f are recursive but only the
outer one is tail recursive.
Tail recursion is a useful property because it enables tail
If you aren't sick of them already, see recursion and tail