Re: Should nil COLLECTION element mean a "nil" candidate for completing-read? Alist doc.

[bojohan+news@dd.chalmers.se (Johan Bockgård)]

Stefan Monnier <monnier@iro.umontreal.ca> writes:

>> (completing-read "ff: " '(nil ("a") ("b)))
>
> A nil there is simply an error.  We don't signal an error, but the
> none of the behaviors you may see is considered as a feature.

     If COLLECTION is an alist (*note Association Lists::), the
     permissible completions are the elements of the alist that are
     either strings, symbols, or conses whose CAR is a string or symbol.
     Symbols are converted to strings using `symbol-name'.  Other
     elements of the alist are ignored. (Remember that in Emacs Lisp,
     the elements of alists do not _have_ to be conses.)  In
     particular, a list of strings or symbols is allowed, even though
     we usually do not think of such lists as alists.

     -- (info "(elisp) Basic Completion")


(But this is not really true--the first element can't be a symbol other
than nil (or lambda).)