Re: Why shouldn't we have a #if .... #else .... #endif construct in Emacs Lisp?

[Ulrich Mueller]

>>>>> On Mon, 28 Aug 2023, Alan Mackenzie wrote:

>> Sorry, I should have been clearer. The full construct would look like
>> this:

>> (when (eval-when-compile (< emacs-major-version 24))
>> (defadvice .....))

> Ah!  So the eval-when-compile gets compiled to a constant nil or t, and
> the byte compiler optimises the test of this out, either compiling or
> not compiling the (defadvice .....).  Thanks!  I hadn't been aware of
> that little detail.

>> So only the test would be evaluated at compile time, the defadvice
>> itself would be compiled normally (or not, if the test fails).

I've just tested with current master. Byte-compiling this:

   (static-if (> emacs-major-version 24)
       (message "new emacs")
     (message "old emacs"))

and this:

   (if (eval-when-compile (> emacs-major-version 24))
       (message "new emacs")
     (message "old emacs"))

results in identical byte code.

> However, when evaluating the containing defun/defmacro rather than byte
> compiling it, the irritating warning message will appear with the e-w-c
> strategem, but not with hash-if.  ;-)

Sorry, I cannot reproduce this problem. Could you give an example?