[Rd] new("call") problem (PR#7490)

[Robert.McGehee at geodecapital.com]

I have found a solution to the new("call") problem that I believe
produces the correct behavior for the default call object, and am also
reclassifying this as a bug, as I believe the current behavior to be
incorrect.

Recap, the following error occurs:
> new("call")
Error in print("<undef>"()) : couldn't find function "<undef>"

It looks like the problem is that the default object for new("call") is
the function "<undef>"(), which does not exist. So, the show() and
print() methods correspondingly fail.

If I initialize the "<undef>"() function at the beginning of my code to
an empty function:

> "<undef>" <- new("function")

then new("call") will then reference an existing (yet empty) object that
is coerced into a call, and the show and print methods correctly display
this object as NULL. Furthermore, I am able to extend this empty call
object to other S4 objects without trouble.

Now:
> "<undef>" <- new("function")
> new("call")
NULL

> str(new("call"))
Formal class 'call' [package "methods"] with 0 slots
 list()

This, I believe is the preferred behavior of new("call"), and I would
contend this fix should be included in the R source.

Best,
Robert

-----Original Message-----
From: McGehee, Robert [mailto:Robert.McGehee at geodecapital.com] 
Sent: Saturday, January 08, 2005 6:06 PM
To: r-devel at stat.math.ethz.ch
Subject: [Rd] new("call") problem


The below looks like the show method has trouble with the default call
object (or that there is no default call object). Not sure if this is a
bug, design problem, or a difficulty on my part using and extending the
call class, but it has caused difficulty for when I want to extend the
call class into other S4 classes.

> new("call")
Error in print("<undef>"()) : couldn't find function "<undef>"

This error pops up when I show an object with an empty call slot.
Error in show("<undef>"()) : Unable to find the argument "object" in
selecting a method for function "show"

I'll leave it up to the developers to designate this as a bug or not,
but I would certainly prefer that new() and show() never reports errors
when an empty object is passed as an argument (of any class).

Best,
Robert

Robert McGehee
Geode Capital Management, LLC
53 State Street, 5th Floor | Boston, MA | 02109
Tel: 617/392-8396    Fax:617/476-6389
mailto:robert.mcgehee at geodecapital.com



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