I think I'm beginning to understand. Tail call elimination is necessary to cope with a system of programming that has deliberately excluded certain other options (eg mutables, in pure functional languages),
Tail recursion is the functional way to write a while loop. To put is another way, a while loop is within stackframe recursion. Ditto for for loops, which are specialized while loops.
Recursion, first (or car), rest (or cdr), and linked lists (non-mutational stacks with the top at the front) work together as a tightly coordinated system. (rest ll) is equivalent to ll[1:] except that rest does not mutate anything. When Python's ll.pop(0) (or ll.pop() removes and returns (first ll), it does mutate ll. Since ll becomes what was previously (rest ll), there is no need for a separate list.rest method.
Python's next(it) is also does the job of both first + rest. As with pop(0), it removes the first item of it, mutates it so it represents the rest of the items in the collection it represents, and then returns the initial item. Again, there is no need for a separate rest(it) funciton. The fundamental computational idea in both systems, beneath the differing syntax and religious wars, is that we can process a collection by processing one item at a time.
-- Terry Jan Reedy -- https://mail.python.org/mailman/listinfo/python-list
