Tail recursion in Python
The hackyness/speed issues aside:<p>When compiling/transpiling/whatever between languages, I have found that relying on regular procedure calls and TCO is generally a lot simpler than having to force the looping facility of one language into the semantics of another language.<p>The only one I can actually imagine porting other loops to is the common lisp loop macro, but that is probably the most flexible looping facility known to man.<p>Edit: and oh, cool thing: racket and guile has expanding stacks and doesn't have a recursion limit other than the whole memory of the computer. This is pretty handy when implementing something like map, since you can write a non-tail-recursive procedure so that you don't have to reverse the list at the end.