[Rd] Why is srcref of length 6 and not 4 ?

[Romain Francois]

Duncan Murdoch wrote:
> On 12/02/2009 7:01 AM, Romain Francois wrote:
>> Hello,
>>
>> Consider this file (/tmp/test.R) :
>>
>> <file>
>> f <- function( x, y = 2 ){
>>    z <- x + y
>>    print( z )
>> }
>> </file>
>>
>> I get this in R 2.7.2 :
>>
>>  > p <- parse( "/tmp/test.R" )
>>  > str( attr( p, "srcref" ) )
>> List of 1
>> $ :Class 'srcref'  atomic [1:4] 1 1 4 1
>>  .. ..- attr(*, "srcfile")=Class 'srcfile' length 4 <environment>
>>
>> and this in R-devel :
>>
>>  > p <- parse( "/tmp/test.R" )
>>  > str( attr(p, "srcref") )
>> List of 1
>> $ :Class 'srcref'  atomic [1:6] 1 1 4 1 1 1
>>  .. ..- attr(*, "srcfile")=Class 'srcfile' <environment: 0x946b944>
>>
>> What are the two last numbers ?
>
> The original design for srcref gave 4 entries: start line, start byte, 
> stop line, stop byte. However, in multibyte strings, bytes don't 
> correspond to columns, so error messages could often report the wrong 
> location according to what a user sees in an editor.  To support the 
> more useful error messages in R-devel, I added two more values: start 
> column and stop column.  With pure ASCII text these will be the same 
> as start byte and stop byte; with UTF-8 text and non-ASCII characters 
> they will be be different.  Other multibyte encodings are only 
> supported if the platform can convert them to UTF-8 (and are not well 
> tested; error reports would be welcome, if there's a way to improve 
> the performance.)
>
> If you are using these for error reports, I recommend using the two 
> new values.  If you are trying to retrieve the text from the source 
> file, use the originals.
>
> Duncan Murdoch
>
>
Thank you Duncan,

I am using this to massage the output of "parse" into a data frame to 
represent it as a tree
(see http://addictedtor.free.fr/misc/sidekick.png)

 > cat( readLines( "/tmp/test.R" ), sep = "\n" )
f <- function( x, y = 2 ){
        z <- x + y
        g <- function( x ){
          print( x )
          xx <- x + 1
        }
        g( x )
}
 >
 > sidekick( "/tmp/test.R", encoding = "utf-8" )
  id parent     mode srcref1 srcref2 srcref3 srcref4               
description
1  1      0 function       1       1       8       1 f <- function(x, y 
= 2) {
2  2      1     name       1      26       1      
26                         {
3  3      1     call       2       2       2      11                z <- 
x + y
4  4      1 function       3       2       6       2        g <- 
function(x) {
5  5      1     call       7       2       7       
7                      g(x)
6  6      4     name       3      20       3      
20                         {
7  7      4     call       4       4       4      13                  
print(x)
8  8      4     call       5       4       5      14               xx <- 
x + 1



-- 
Romain Francois
Independent R Consultant
+33(0) 6 28 91 30 30
http://romainfrancois.blog.free.fr