Mailing List Archive: Re: vargs function (or "r-expression)

[REBOL] Re: vargs function (or "r-expression)

From: santilli::gabriele::gmail::com at: 7-May-2007 12:52


2007/5/6, Tim Johnson <tim-johnsons-web.com>:

> I have a need for an "r-expression", that is - a class of functions that
> will be evaluated by 'do as part of a block and can have 0 or more
> arguments.
> example:
>  do [vargs "two" 3]
>  do [vargs "two" 3 "four"]
>  do [vargs "two" 3 none "four"]
>  do[vargs]

You can also just call it with:

   (vargs "two" 3)
   (vargs "two" 3 "four")
   (vargs)

etc. (More Lispy. ;)

However, I don't think this is a great idea when you have many
arguments, and it'll cause problems if you forget the parens. If you
need variable nuber of arguments, the best way is:

  vargs: func [args [block!] /local a b c] [
      set [a b c] reduce args
      ?? a ?? b ?? c
  ]

>> vargs []
a: none
b: none
c: none
== none
>> vargs [1 2]
a: 1
b: 2
c: none
== none
>> vargs [2 + 2 3]
a: 4
b: 3
c: none
== none

This is the starting point to make your ARGS block a dialect. :)

HTH,
    Gabriele.