No No! The parent environment is **not necessarily** the enclosing
environment. The difference is crucial. R looks for free variables in the
enclosing, **not** the parent environment (although they are often the
same). Please read about lexical scoping in R in the "R language
definition" manual, or in online resources. That will explain why R (and
other functional programming languages) do things this way. There is a lot
that you do not understand.
Bill's clever solutions and cautions may also not make sense until you do
your homework.
Cheers,
Bert
On Thu, Sep 12, 2013 at 2:36 PM, Gang Peng <michael.gang.p...@gmail.com>wrote:
> Hi Bert,
>
> Thanks for the explanation.
>
> In R, it first search the local environment and then the parent
> environment until the root environment (empty environment). I have a
> concern, when I write a function, I may write a variable name wrong by
> typo. But by coincidence, this variable name is defined in the parent's
> or the grandparent's environment, it is very hard to find this bug (It took
> me almost a day to find out it). Just don't know why R do it like this.
>
> Thanks,
> Michael
>
>
>
> 2013/9/12 Bert Gunter <gunter.ber...@gene.com>
>
>> Michael and Sarah:
>>
>> 1. Actually the original claim -- that R will search the global
>> environment if it does not find a free variable in the function environment
>> -- is not strictly true. It will search the function's enclosure and then
>> on up the tree of enclosures. In this case, the enclosure was the global
>> environment, but that is not always the case.
>>
>> 2. Sarah has answered one interpretation of your question. Another might
>> be -- how can you do things to throw an error when free variables are
>> encountered in a function. A qualified answer -- qualified, because there
>> are probably some clever ways to set this up that I can't and won't try to
>> think of -- is that you can't: you are defeating R's functional programming
>> paradigm by requesting such behavior. Or to put it another way: don't
>> do/expect this. Follow Sarah's recommendation instead.
>>
>> Cheers,
>> Bert
>>
>>
>> On Thu, Sep 12, 2013 at 2:08 PM, Sarah Goslee <sarah.gos...@gmail.com>wrote:
>>
>>> Hi,
>>>
>>> You need to specify that a is an argument to the function:
>>>
>>> On Thu, Sep 12, 2013 at 3:56 PM, Gang Peng <michael.gang.p...@gmail.com>
>>> wrote:
>>> > For example:
>>> >
>>> > a <- 1
>>> >
>>> > f <- function(b){
>>> > return(a+b)
>>> > }
>>> >
>>>
>>> f <- function(b, a) {
>>> return(a+b)
>>> }
>>>
>>> > when we call function f(2), r will search the local environment first,
>>> if
>>> > it cannot find a, it will search global environment, and return 3. How
>>> to
>>> > avoid r searching the global environment and return an error when we
>>> call
>>> > this function?
>>>
>>> The function will now give an error if a is not specified.
>>>
>>> Sarah
>>>
>>> --
>>> Sarah Goslee
>>> http://www.functionaldiversity.org
>>>
>>> ______________________________________________
>>> R-help@r-project.org mailing list
>>> https://stat.ethz.ch/mailman/listinfo/r-help
>>> PLEASE do read the posting guide
>>> http://www.R-project.org/posting-guide.html
>>> and provide commented, minimal, self-contained, reproducible code.
>>>
>>
>>
>>
>> --
>>
>> Bert Gunter
>> Genentech Nonclinical Biostatistics
>>
>> Internal Contact Info:
>> Phone: 467-7374
>> Website:
>>
>> http://pharmadevelopment.roche.com/index/pdb/pdb-functional-groups/pdb-biostatistics/pdb-ncb-home.htm
>>
>>
>
>
--
Bert Gunter
Genentech Nonclinical Biostatistics
Internal Contact Info:
Phone: 467-7374
Website:
http://pharmadevelopment.roche.com/index/pdb/pdb-functional-groups/pdb-biostatistics/pdb-ncb-home.htm
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