Re: locate-file in Emacs

[Richard Stallman <rms@gnu.org>]

    Based on the information here, I think I'll go ahead and implement
    the functionality on top of `openp' with just a `predicate' argument
    and without backward compatibility for `mode'.

We should support backward compatibility values of MODE such as
`executable' and `writable'.  That is a clean enough interface,
so there is no particular downside to supporting it.

We could allow predicates as alternative values for the same argument,
or we could add another optional argument PREDICATE.

    But I have one question left: should the `file-directory-p' check be enforced
    independently from `predicate' ?

Definitely yes--by default.  The default should be to
return only files, not directories.

There could be an additional optional argument which says "accept
directories too."  Perhaps it could also have a way to specify
that you want directories only.