RE: [External] : Re: Always-true predicate?

[Drew Adams]

> > But my main gripe is about options whose values can only be
> > functions, and nothing else.  No one will convince me that
> > Emacs developers cannot come up with meaningful values that
> > aren't functions for some option.
> 
> Yeah, that's true.  Having nil/t values is often handy.
> I guess the only reason for not adding those is laziness.

I generally agree with where I think you're both
heading (converging).

I'll add this to what Eli said about there being
a difference between having an option whose only
possible values are functions and one that allows
a function value but also allows some other values
(with which I agree):

The typical case for a function-only option is for
the default value to be a named function.  Eli's
point is that if you want to change the option
value then you need to provide a function name or
a lambda form.  Error prone (for lambda) and can
require some Elisp knowledge (for lambda).

But it's also possible for more than one named
function to be predefined and mentioned in the
doc string.  In that case, picking one of _those_
names is not very different from the defcustom
providing a `choice' that includes values that
correspond to those names (as well as a catch-all
arbitrary function choice).