From mboxrd@z Thu Jan 1 00:00:00 1970 Path: news.gmane.io!.POSTED.blaine.gmane.org!not-for-mail From: LdBeth Newsgroups: gmane.emacs.devel Subject: Re: Why shouldn't we have a #if .... #else .... #endif construct in Emacs Lisp? 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List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: emacs-devel-bounces+ged-emacs-devel=m.gmane-mx.org@gnu.org Original-Sender: emacs-devel-bounces+ged-emacs-devel=m.gmane-mx.org@gnu.org Xref: news.gmane.io gmane.emacs.devel:309525 Archived-At: >>>>> In >>>>> Alan Mackenzie wrote: acm> Hello, Emacs. acm> In Emacs Lisp we have no such construct. This is a Bad Thing. acm> More and more, especially recently, irritating warning messages are acm> occurring for, for example, obsolete variables and functions inside acm> conditionals which ensure they aren't used. For example: acm> (when (< emacs-major-version 24) acm> (defadvice .....)) acm> produces the warning about defadvice being obsolete. (I haven't actually acm> tested this example). What we really want here is for the defadvice only acm> to be _compiled_ when (< emacs-major-version 24), rather than compiled acm> unconditionally and not run. acm> I propose a new function, hash-if, which would do what we want. The acm> above example could then be written something like: acm> (hash-if (< emacs-major-version 24) acm> (defadvice .....) acm> (advice-add .....)) Have a look at `static.el' from APEL https://github.com/wanderlust/apel It provides `static-if' and other useful macros. (defmacro static-if (cond then &rest else) "Like `if', but evaluate COND at compile time." (if (eval cond) then `(progn ,@ else)))