From mboxrd@z Thu Jan 1 00:00:00 1970 Path: news.gmane.io!.POSTED.blaine.gmane.org!not-for-mail From: Pip Cet Newsgroups: gmane.emacs.devel Subject: Re: Always-true predicate? Date: Wed, 17 Feb 2021 19:31:28 +0000 Message-ID: References: <875z2qoqc6.fsf@gnus.org> <87h7ma25so.fsf@tcd.ie> <8735xu33jy.fsf@gnus.org> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Injection-Info: ciao.gmane.io; posting-host="blaine.gmane.org:116.202.254.214"; logging-data="8946"; mail-complaints-to="usenet@ciao.gmane.io" Cc: "Basil L. 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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" Xref: news.gmane.io gmane.emacs.devel:265059 Archived-At: On Wed, Feb 17, 2021 at 7:19 PM Lars Ingebrigtsen wrote: > Pip Cet writes: > >> > Would it make sense to add a function that's exactly the opposite of > >> > `ignore' (for symmetry and convenience)? > > t > You want to defun t? (Resisting the temptation to answer with the same single-letter response...) Strictly speaking, I only want to special-case it so (funcall t ...) is t. Defuning it would be one way of achieving that, but not the only possible one. (lambda (&rest args) t) is the top element of the lattice of functions in several senses: it's the pointwise logical or of all functions, it has the largest possible codomain, and it's the universal predicate. Such top elements are usually represented as 't'. Note that ignore is the bottom element of only two of those lattices, so there's less of an argument to be made for it. An always-throwing function that accepts no possible argument list would make just as much sense. (apply nil), of course, should continue to crash Emacs.