Re: Detect if Emacs is running in -nw mode

[Rupert Swarbrick <rswarbrick@gmail.com>]

On Sun, 30 Mar 2008 16:45:57 +0200, Lennart Borgman (gmail) wrote:
> The documentation should be exact enough to show that. If not then it is
> a documentation bug.
> 
> In this case it says "body forms", not "body form". A form is something
> inside a pair of (). So it is ok with several functions here.
> 
> If it was not you could have used progn for example.

I'm not sure and if I'm wrong, Christian, please correct me, but:

I think the problem is that Christian doesn't know what "body" means. In 
lisp, a function is defined using something called a lambda list, so I 
might define a function foo like:

(defun foo (arg1 arg2 arg3) (do-some-stuff))

In this case arg1, arg2 and arg3 are three different arguments, so we'd 
call foo like this

(foo 1 2 3)

Great. However, if you want to write a useful unless function/macro, you 
want to allow any number of elements in the list - a bit like varargs do 
in C, if you know about that.

Anyhow, you write something like

(defun bar (arg1 &rest others) (do-some-stuff))
or (pretty much equivalently)
(defun bar (arg1 &body others) (do-some-stuff))

For bar, arg1 is just a normal argument. But others is a bit magic:

(bar 1 2 3 4 5 6)

sets arg1 to 1 and others to (2 3 4 5 6)   (a list). Now, unless is 
actually a macro and the bit it does next depends on a whole new can of 
worms based on macro expansion and ,@ but I'm not going to go into that. 
The main point however is that the documentation says:

> -- 
> |unless is a Lisp macro in `subr'.
> |(unless COND &rest BODY)
>                                           |
> |If COND yields nil, do BODY, else return nil.
> -- 

So the &rest bit means that body can contain as much as you like. FWIW, 
unless executes BODY in a progn, so for example

(unless (function-returning-nil) 1 2 3)

evaluates to 3. Not that that matters in this situation.

Phew. That was more than I intended to write! Hope it makes things a 
little clearer.

Rupert