possible bug in formals

Dear Brian and Uwe,

Thanks a lot for the clarification.
I made the naive assumption that numeric constants in R are similar to
those in C. 

Two questions still remain:

(1) when I have a function 

    f<- function(a=1,b=-1) { a+b }

    is it safe to use 

    val <- as.character(deparse(formals(f)$b))

    to obtain a string that contains the default value for
    argument "b". (Does is also work for other arguments with some 
    default of arbitrary class?)

(2) I have seen that packages like gWidget (in function ggenericwidget)
    use a statement like

    switch(class(formals(f)$b),
	numeric = { .... },
        character = { .... },
        class = { .... }, ....

    for automatically processing function arguments.
    in the case of "b=-1" this procedure obviously fails.
    (I found this behavior of 'formals' while playing around with 
    packages "gWidgets" and "fgui" from CRAN).

    Is there a safe workaround for this problem?

    That is, is there a safe function that returns class
    "numeric" for an exresion like "-1" or "-Inf"?

Josef

Documented too: from ?NumericConstants

      Note that a leading plus or minus is not regarded by the parser as
      part of a numeric constant but as a unary operator applied to the
      constant.



On Sun, 23 May 2010, Uwe Ligges wrote:

On 23.05.2010 16:14, Josef Leydold wrote:

Hi,

I am a little bit surprised by the following output of
'formals'. Is this the intended behavior?

f<- function(a=1,b=-1) { a+b }
class(formals(f)$a)

[1] "numeric"

class(formals(f)$b)

[1] "call"


Josef

Yes, the arguments have not yet been evaluated, hence -1 is still a language 
object.

Try to write
f<- function(a= +1, b= -1) { a+b }
and you will find that this is a fascinating feature.

Uwe Ligges

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