[Rd] possible bug in formals
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
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Josef Leydold | WU (Vienna University of Economics and Business)
| Institute for Statistics and Mathematics
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Augasse 2-6 | Tel. +43 1 31336 4695
A-1090 Vienna | FAX+43 1 31336 774
European Union | email josef.leyd...@wu.ac.at
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Re: [Rd] possible bug in formals
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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Re: [Rd] Is it possible to generate an error when a function is reassigned?
thmsfuller...@gmail.com wrote: Hello All, length() is a function. If I accidentally assign something else to length, it will give me some unexpected results. Although the freedom to redefine any funcion maybe good in sometime, it may be unwanted in many other cases. Is there a way to forbidden such changes on functions? You aren't changing length(), you're creating a new function with the same name that hides the original one. The distinction is important because packages with namespaces will not be affected by your error, it's not really as serious as you might think. The general advice to protect yourself from mistakes like this is to limit how much of your code you keep in the global environment. Keep your code in scripts and source them into an empty environment, or (better) put your code into a package and use a namespace. If you make a mistake and hide an important function you'll still cause local problems, but you may find it easier to fix them. Duncan Murdoch __ R-devel@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-devel
