Re: optional arguments in CLush functions?

Allowing null pointers to be tested like this in C-lush
would be horribly unsafe.

Thankfully, there is a simple solution to your problem
by using macros (thank you lisp.gods):

================================================================
(dm my-plus (dummy a b . cl)
  (if cl
      `(do-stuff ,a ,b ,(car cl))
    `(let ((c (clone-array ,a))) (do-stuff ,a ,b c))))

(printf "with 2 arguments:\n")
(pretty (macro-expand (my-plus x y)))

(printf "\nwith 3 arguments:\n")
(pretty (macro-expand (my-plus x y z)))
================================================================

Loading the above code produces this:

with 2 arguments:
(let ((c (clone-array x)))
  (do-stuff x y c) )

with 3 arguments:
(do-stuff x y z)


  -- Yann


On Tuesday 15 November 2005 07:56 pm, Ralf Juengling wrote:
> Hi,
>
> When I write C functions where the arguments are objects
> (pointers) and want to make some of the arguments optional,
> an easy way to do so is by the convention that NULL pointers
> indicate absent arguments.
>
> I'd like to do something similar with CLush. For the sake
> of an example, say I might want to write my own vector copying
> routine and if three args are provided, then the last arg is
> taken to be the storage for the result.
>
> (defun my-plus (a b c)
>    ((-idx1- (-double-)) a b c)
>
>    (if (= (to-gptr c) ())
>        (let ((c (clone-array a)))
>          ;; do stuff
>          c)
>      ;; do other stuff and use input c
>      c))
>
> With two args the invocation would look like
>
> (my-plus u v NULL)  ;; NULL some new symbol
>
> with three args it would look like
>
> (my-plus u v w)
>
>
> Of course, it doesn't work currently--at least not the
> way I tried. There are a number of questions here:
>
> 1. Is there any way, currently, to do what I want to do?
>
> 2. When you try to create a NULL ptr (a gptr object with
>     value NULL) in lush, the result is nil. When the CLush
>     compiler encounters a nil, it considers it a boolean
>     value rather than a NULL pointer.
>     Maybe we need to add a new symbol for this purpose to
>     lush/CLush, |NULL| say?
>
> 3. Would it be possible to change the CLush compiler to
>     make it accept a NULL ptr as arguments where the
>     corresponding formal parameter is an object?
>
> Any comments appreciated.
> Thanks,
> Ralf
>
>
>
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