Re: Always-true predicate?

[Pip Cet <pipcet@gmail.com>]

On Wed, Feb 17, 2021 at 7:19 PM Lars Ingebrigtsen <larsi@gnus.org> wrote:
> Pip Cet <pipcet@gmail.com> 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.