(non)-evaluation of an optional argument

["Patrick Joseph" <patrick_nospam@hotmail.com>]

Hi,

I have a question about the evaluation of an optional argument of a 
function. Let:
myfct _ function(a,...) {
        dots <- match.call(expand.dots = F)$...
        print(dots)
        if(!is.null(dots$b))
                return(a + dots$b)
        else return(a)
}

When I do the call myfct(10), obviously it prints "list()" and returns 10.
When I do the call myfct(10,b=9), it prints "list(b = 9)" and returns 19. 
Ok.
Now if I define tmp<-9 and do the call myfct(10,b=tmp), it prints "list(b = 
tmp)" and returns the error message: "Error in a + dots$b: Non-numeric 
second operand".
Is it possible to force the evaluation of tmp when calling the function?

Thank you for any hint,
Patrick

(I'm using S-Plus 4.5 on Windows 2000)

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