Topic: Make an argment optional?

[TimSpangler]

How is this done?  I have a routine:

Code: [Select]

(defun FilterList (AList Filter  / TruncString )

(if (not Filter)
(alert "No Filter Set")
(progn
(setq FilterList '())
(foreach Obj Alist
(setq TruncString(substr(nth 0(TGS:StringToList(cdr Obj)";"))3 4))
(if (= (strcase Filter) TruncString)
(setq FilterList (cons Obj FilterList))
)
)
FilterList
)
)
)
that take 2 arguments but I only really need the first one all of the time.  If the second one is supplied then I want to use it.  How do I go about this?

BTW: This routine takes a list and a filter and checks the filter against a certian thing in the list if it matches the filter it adds it to a new list which will be sent to a list box.  The reason for the optional argument is if no filter is suppied I want the whole list sen to the listbox

Thanks

[MP]

Pass but one argument, a list. Need more info than this?

[MP]

Some ideas ... coded blind / not tested, as I don't have one of the functions you're calling.

Code: [Select]

(defun FilterList ( arguments / filter result )

    ;;  first item in arguments is alist
    ;;
    ;;  second item in arguments is filter
   
    (cond
   
        (   (setq filter (cadr arguments))

            (foreach item (car arguments) ;; alist (implied)
           
                (if
                   
                    (eq (strcase filter)
                        (strcase
                            (substr    
                                (car
                                    (TGS:StringToList
                                        (cdr item)
                                        ";"
                                    )
                                )
                                3
                                4
                            )
                        )    
                    )
                   
                    (setq result
                        (cons
                            item
                            result
                        )
                    )
                )
            )
           
            ;;  even though you can have a local variable
            ;;  named the same as the function hosting it
            ;;  I think this is a better tact
           
            result
           
        )
        ((alert "No Filter Set"))
    )
)

;;  formerly you'd call FilterList thusly

(FilterList alist filter)

;;  now like so

(FilterList (list alist filter))

;;  or

(FilterList (list alist))

[CAB]

Here is some reading material...
http://www.theswamp.org/phpBB2/viewtopic.php?t=1922&highlight=optional+variable

http://www.theswamp.org/phpBB2/viewtopic.php?t=1222&highlight=optional+argument