R parser for If-else
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