Re: Insert one of the flags automatically with tab completion.

[Emanuel Berg via Users list for the GNU Emacs text editor <help-gnu-emacs@gnu.org>]

Hongyi Zhao wrote:

>> Note that interactive and non-interactive use are not
>> identical in one aspect ...
>
> Interactive is interacting with user as a command.
> Non-interactive is called from within lisp code.

Yes, interactive is a command, M-x CMD RET, or a keybinding.

Non-interactive is from Lisp ...

(`call-interactively' is the exception that proves the rule,
and it should only be used when ... there is a reason to :))

But that's not what I refered to actually, if you study the
code you see the "nil t" that you asked about in the
other thread -

(defun atomic-position (flag)
  (interactive
   (list
    (completing-read
     "flag: " '("alat" "angstrom" "bohr" "crystal" "crystal_sg") nil t) ))
  (insert (format "Atomic position: %s\n" flag)) )

- and if you take a look at the docstring of `completion-read'
you see that these arguments are for the

  &optional PREDICATE REQUIRE-MATCH

so the first nil says PREDICATE should be nil, it is already
nil by default but we want to say that REQUIRE-MATCH should be
t, so we say that PREDICATE is nil just to get to
REQUIRE-MATCH if you follow, then we say it is t.

And this is the difference from non-interactive use, because
there is no such thing in the non-interactive part of the
function. You can send any "flag" argument from Lisp and it
will be processed.

(atomic-position "darn")

But M-x atomic-position RET darn RET ... try it.

Read (or look at) the docstrings, especially the
interface/prototype part, to all functions you use ...

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