R help - Oct 2016 - strange output of cat function used in recursive function

Hello Dear R-help

I  tried to understand how recursive programming works in R. Bellow is
simple recursive function.

binary1 <- function(n) {
  if(n > 1) {
    binary(as.integer(n/2))
  }
  cat(n %% 2)
}
When I call binary1(10) I get 1010. I believe that cat function stores
value to a buffer appending values as recursion proceeds and at the
end it prints the buffer. Am I right?

I tried to modify the function to get some understanding:

binary2 <- function(n) {
  if(n > 1) {
    binary2(as.integer(n/2))
  }
  cat(n %% 2, sep=",")
}

With call binary2(10) I get also 1010. Why the output is not separated
by commas?

If I use in binary2 function cat(n %% 2, ",") on last line, the output
is separated. Outside recursive function the cat function prints
separated output in both cases e.g. cat(c(1:10), sep=",") and
cat(c(1:10), ",")

Derek

> On Oct 1, 2016, at 8:44 AM, Jan Kacaba <jan.kacaba at gmail.com>
wrote:
> 
> Hello Dear R-help
> 
> I  tried to understand how recursive programming works in R. Bellow is
> simple recursive function.
> 
> binary1 <- function(n) {
>  if(n > 1) {
>    binary(as.integer(n/2))
>  }
>  cat(n %% 2)
> }
Did you mean to type "binary1(as.integer(n)"?
> When I call binary1(10) I get 1010. I believe that cat function stores
> value to a buffer appending values as recursion proceeds and at the
> end it prints the buffer. Am I right?
No. Read the ?cat help page. It returns NULL. The material you see at the
console is a side-effect.
> 
> I tried to modify the function to get some understanding:
> 
> binary2 <- function(n) {
>  if(n > 1) {
>    binary2(as.integer(n/2))
>  }
>  cat(n %% 2, sep=",")
> }
> 
> With call binary2(10) I get also 1010. Why the output is not separated
> by commas?
I think because there is nothing to separate when it prints (since there was no
"buffer".
> 
> If I use in binary2 function cat(n %% 2, ",") on last line, the
output
> is separated. Outside recursive function the cat function prints
> separated output in both cases e.g. cat(c(1:10), sep=",") and
> cat(c(1:10), ",")
> 
> Derek
> 
> ______________________________________________
> R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see
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http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
David Winsemius
Alameda, CA, USA

2016-10-01 18:02 GMT+02:00 David Winsemius <dwinsemius at
comcast.net>:
>
>> On Oct 1, 2016, at 8:44 AM, Jan Kacaba <jan.kacaba at gmail.com>
wrote:
>>
>> Hello Dear R-help
>>
>> I  tried to understand how recursive programming works in R. Bellow is
>> simple recursive function.
>>
>> binary1 <- function(n) {
>>  if(n > 1) {
>>    binary(as.integer(n/2))
>>  }
>>  cat(n %% 2)
>> }
>
> Did you mean to type "binary1(as.integer(n)"?
Yes I meant that.
>> When I call binary1(10) I get 1010. I believe that cat function stores
>> value to a buffer appending values as recursion proceeds and at the
>> end it prints the buffer. Am I right?
>
> No. Read the ?cat help page. It returns NULL. The material you see at the
console is a side-effect.
>>
>> I tried to modify the function to get some understanding:
>>
>> binary2 <- function(n) {
>>  if(n > 1) {
>>    binary2(as.integer(n/2))
>>  }
>>  cat(n %% 2, sep=",")
>> }
>>
>> With call binary2(10) I get also 1010. Why the output is not separated
>> by commas?
>
> I think because there is nothing to separate when it prints (since there
was no "buffer".
If I use function:
binary3 <- function(n) {
if(n > 1) {
   binary3(as.integer(n/2))
  }
   cat(n %% 2, ",")
 }

and call binary3(10) the console output is separated. So there must be
some kind of buffer and also it looks like there is some inconsistency
in how cat function behaves. Probably there is other explanation.