On 07/01/2012 09:27 AM, Eli Barzilay wrote:
There rare cases where it is useful to have a value that means that no argument was passed to a function. In many of these cases there is a plain value that is used as that mark, with the most idiomatic one being #f, but sometimes others are used. IMO, while such uses of #f are idiomatic, they're a hack where an argument's domain is extended only to mark "no argument".
I believe this is why CL lambda lists allow another variable name when specifying optional parameters.
http://www.lispworks.com/documentation/HyperSpec/Body/03_dab.htm http://www.gigamonkeys.com/book/functions.html (defun f (&optional (arg 'default-value arg-supplied?)) (if arg-supplied? 'real-value 'default-value)) Matlab's nargin and nargout are another interesting approach. http://www.mathworks.com/help/techdoc/ref/nargin.html http://www.mathworks.com/help/techdoc/ref/nargout.html A (supplied? arg) special form might also work. - Daniel _________________________ Racket Developers list: http://lists.racket-lang.org/dev
