R help - Feb 2009 - R parser for If-else

Hi list,

I don't know if somebody has spent a lot of time debugging strange
problems with if else positioning - the parser seems to recognize only
the syntax bellow - this is the only way of making these pieces of
code to work.

As far as i'm concerned, no examples were available (it would be so
awesome to have them in the introductory manual!)

#Try to change the placement of the keywords and you are dead! 4 examples
Ex1:
if (1==1){
?print('if')
?print('if again')
?}else
?print('else')

Ex2:
if (2==2) print('if') else print('else')

Ex3:
if (2==2){
?print('if')
?print('if again')
?}else
?{
?print('else')
?print('else2')
?}

Ex4:
if (2==2){
?print('if')
?print('if again')
}else print('else')



cheers,
-------------------------------------
Daniela

>>>>> "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.