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) Here the both calls to fib are recursive but only the outer one is tail recursive. See tail recursion optimisation, and, if you aren' t sick of them already, recursion, tail recursion. [Jargon File] (1996-02-22)
