Re: question about optional arguments

[David Kastrup]

"leo" <halloleo@noospaam.myrealbox.com> writes:

> "David Kastrup" <dak@gnu.org> wrote in message
> x57k03c5rm.fsf@lola.goethe.zz">news:x57k03c5rm.fsf@lola.goethe.zz...
> > "leo" <halloleo@noospaam.myrealbox.com> writes:
> >
> > > i want to call dired-get-marked-files with the specific value 1 for
> > > secend argument arg but without a value for the first argument localp,
> >
> > Is that a trick question?
> 
> no, probably just a stupid question, sorry.
> 
> > (dired-get-marked-files nil 1)
> 
> thanks david, i didn't know that nil is as good as no argument.

Then it would not have done harm to look up argument lists in the
manual:

   A call to the function requires one actual argument for each of the
REQUIRED-VARS.  There may be actual arguments for zero or more of the
OPTIONAL-VARS, and there cannot be any actual arguments beyond that
unless the lambda list uses `&rest'.  In that case, there may be any
number of extra actual arguments.

   If actual arguments for the optional and rest variables are omitted,
then they always default to `nil'.  There is no way for the function to
distinguish between an explicit argument of `nil' and an omitted
argument.  However, the body of the function is free to consider `nil'
an abbreviation for some other meaningful value.  This is what
`substring' does; `nil' as the third argument to `substring' means to
use the length of the string supplied.

-- 
David Kastrup, Kriemhildstr. 15, 44793 Bochum