Some of them.<p>If you have exponential run times, I don&#x27;t think tail call optimization would help you.<p>Of course, that claim with the exponential run time in the first place is ludicrous: sure, you&#x27;ll have a hard time implementing the Ackermann function with loops.  But that&#x27;s a problem with loops, not with function calls.<p>I say function calls here, because recursion in function is just a special case of function calls.  You gotta have functions in a modern language in any case, so recursion comes for free.  No need to introduce another concept like loops and clutter up your language.