Both 'for' and 'next' return TRUE from is.function
is.function('for')
is.function('next')
Not at an R console at the moment but I did check this earlier today. Thinking
of it as different is definitely the way to think about it. (ISTR Bert and I
have had this exchange in the past.)
--
Best
David
Sent from my iPhone
> On Apr 16, 2017, at 9:50 PM, Bert Gunter <bgunter.4...@gmail.com> wrote:
>
> David et. al.:
>
> "this levels is the level where you realize that the `for` function is
> different from most other R functions. It is really a
> side-effect-fucntion. "
>
> for(), while(), if(), next, etc. are *not* functions.
>
> ?for says: "These are the basic control-flow constructs of the R language."
>
> They do not "return" values. They control program flow, whence what
> you call "side effects" are actually expressions that are parsed and
> evaluated
>
> viz.
>
>> if(TRUE)10
> [1] 10
>
> ## but
>
>> if(FALSE) 5
> ## nothing is returned, not even NULL
>> for(i in 1:3) i
> ## Ditto
>
>> z <- NULL
>> z <- for(i in 1:3)i
>> z
> NULL ## still
>
> Cheers,
> Bert
>
>
>
>
> Cheers,
> Bert
>
>
>
>
> Bert Gunter
>
> "The trouble with having an open mind is that people keep coming along
> and sticking things into it."
> -- Opus (aka Berkeley Breathed in his "Bloom County" comic strip )
>
>
>> On Sun, Apr 16, 2017 at 8:12 PM, David Winsemius <dwinsem...@comcast.net>
>> wrote:
>>
>>> On Apr 16, 2017, at 7:26 PM, Ramnik Bansal <ramnik.ban...@gmail.com> wrote:
>>>
>>> In the code below
>>>
>>>
>>> *ff <- function(n){ for(i in 1:n) (i+1)}*
>>>
>>> *n<-3;ff(n)->op;print(op)*
>>>
>>> Why doesnt *print(op) * print 4 and instead prints NULL.
>>> Isnt the last line of code executed is *i+1 * and therefore that should be
>>> returned instead of NULL
>>>
>>> instead if I say
>>> *ff <- function(n){ (n+1) }*
>>>
>>> Then
>>> *n<-3;ff(n)->op;rm(n);print(op)*
>>> gives 4 as output.
>>>
>>> My question is *Which *is considered as the last line in a functoin for the
>>> purpsoe of default return ? And under what conditions ?
>>
>> It's probably a good thing that you are confused. It suggests that you are
>> actually "getting" the R-paradigm. Unfortunately for the new user of R,
>> there are several levels of understanding to pass through. First, you
>> realize that function-results need to be assigned to names in order to
>> persist. Then there is the next level where you discover that there are
>> exceptions to that rule: this levels is the level where you realize that the
>> `for` function is different from most other R functions. It is really a
>> side-effect-fucntion. The assignments made within its body actually persist
>> in the global environment. AND it returns NULL. It shares this anomalous
>> behavior with `while` and `repeat`.n Almost all functions are invoked with a
>> possibly empty argument list. The next and break functions have implicit
>> paired (empty) parentheses.
>>
>> (My personal opinion is that this is not adequately advertised. Perhaps it
>> is an attempt to get people to migrate away from "Fortran-coding" behavior?)
>>
>> --
>> David.
>>
>>
>>>
>>> -Thanks,
>>> Ramnik
>>>
>>> [[alternative HTML version deleted]]
>>>
>>> ______________________________________________
>>> R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see
>>> 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.
>>
>> David Winsemius
>> Alameda, CA, USA
>>
>> ______________________________________________
>> R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see
>> 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.
______________________________________________
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