Re: Understanding dotimes skipping by 2

[Eric Abrahamsen]

Marco Wahl <marcowahlsoft@gmail.com> writes:

> Tim Johnson <tim@akwebsoft.com> writes:
>
>> the following code snippet is as follows:
>> (setq l `(1 2 3 4 5 6 7 8 9 0))
>
>> ;; iterate through a list two elements at a time
>> (let ((x 0))
>>   (dotimes (/ (length l) 2)
>>     (progn
>>       (insert (format "%s %s, " (nth x l) (nth (+ x 1) l)))
>>       (setq x (+ x 2)))))
>>
>> ;; and below are the results
>> 1 2, 3 4, 5 6, 7 8, 9 0, nil nil, nil nil, nil nil, nil nil, nil nil, 2
>>
>> I'm confused about the output (nil etc...)which follow the expected numbers. 
>> could someone explain?
>> P.S. I get the same output without the `progn form
>
> Looks like "/" is a variable which gets bound to the values of 0 up to
> (length l) and the result of the loop is 2.
>
> It's in the documentation (C-h f dotimes).

To add to that -- if you want to consume a loop two elements at a time,
you'd be better off using `cl-loop' and its "by" keyword.