Strange elisp byte-compiler warning about unused variables

Question

The following elisp code inserts hello world! 10 times:

-*- lexical-binding: t -*-
(dotimes (i 10) (insert "hello world!\n"))

If I byte-compile that code, I get the following message:

hellos.el:2:1:Warning: Unused lexical variable `i'

This is strange ... i is used to count from 0 to 9, even if it is not used in the repeated code. How am I supposed to loop 10 times ?!

Even stranger, the warning message disappears if I set

-*- lexical-binding: nil -*-

Go figure ...

Is this a bug (admittedly minor) in the emacs compiler? Is there a way to loop 10 times without using a counting variable?

Answer 1

You don't use i and that's what the byte-compiler tells you. To let the byte-compiler know that you're aware of the fact that the variable is unused, give it a name that starts with an underscore. E.g.

(dotimes (_ 10) ...)

or

(dotimes (_i 10) ...)