I actually like the 'recur' better than implicit tail-call optimization. It does what it says on the tin. If you don't use recur, you get unoptimized recursion,

I actually like the 'recur' better than implicit tail-call optimization. It does what it says on the tin. If you don't use recur, you get unoptimized recursion, and more importantly: where you can't make a function tail-recursive, you can't use 'recur', because it is a compiler error.