[R] R parser for If-else

[Robin Hankin]

I too have had many problems with if-else.

My solution is to always always always
use the line

"} else {"

in any if-else construction.  This guarantees that
there won't be problems of the sort discussed here.

HTH

rksh



Martin Maechler wrote:
>>>>>> "D" == Dani  <danicyber at gmail.com>
>>>>>>     on Tue, 24 Feb 2009 14:09:36 -0800 writes:
>>>>>>             
>
>     D> Hi list,
>     D> I don't know if somebody has spent a lot of time debugging strange
>     D> problems with if else positioning - the parser seems to recognize only
>     D> the syntax bellow - this is the only way of making these pieces of
>     D> code to work.
>
>     D> As far as i'm concerned, no examples were available (it would be so
>     D> awesome to have them in the introductory manual!)
>
>     D> #Try to change the placement of the keywords and you are dead! 
> ["dead"?] 
>
> Oh dear... 
> Note this has nothing to do with   if( ) .. else ..
> but indeed with how things are parsed.
>
> I think this is FAQ (or should become one):
>
> ?if [the help page you really should read before spending too
>      much time or even post to R-help]  
> has the following section
>
>  >      Note that it is a common mistake to forget to put braces ('{ .. }')
>  >      around your statements, e.g., after 'if(..)' or 'for(....)'.
>  >      In particular, you should not have a newline between '}' and 
>  >      'else' to avoid a syntax error in entering a 'if ... else'
>  >      construct at the keyboard or via 'source'. For that reason, one
>  >      (somewhat extreme) attitude of defensive programming is to always
>  >      use braces, e.g., for 'if' clauses.
>
> Regards,
> Martin Maechler, ETH Zurich
>
>
>     D> Ex1:
>     D> if (1==1){
>     D>  print('if')
>     D>  print('if again')
>     D>  }else
>     D>  print('else')
>
>     D> Ex2:
>     D> if (2==2) print('if') else print('else')
>
>     D> Ex3:
>     D> if (2==2){
>     D>  print('if')
>     D>  print('if again')
>     D>  }else
>     D>  {
>     D>  print('else')
>     D>  print('else2')
>     D>  }
>
>     D> Ex4:
>     D> if (2==2){
>     D>  print('if')
>     D>  print('if again')
>     D> }else print('else')
>
>
>
>     D> cheers,
>     D> -------------------------------------
>     D> Daniela
>
>     D> ______________________________________________
>     D> R-help at r-project.org mailing list
>     D> https://stat.ethz.ch/mailman/listinfo/r-help
>     D> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
>     D> and provide commented, minimal, self-contained, reproducible code.
>
> ______________________________________________
> R-help at 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.
>   


-- 
Robin K. S. Hankin
Uncertainty Analyst
University of Cambridge
19 Silver Street
Cambridge CB3 9EP
01223-764877