I see. Thanks a lot for your help.
M.
2013/9/12 Bert Gunter <gunter.ber...@gene.com>
> 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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