R devel - Aug 2015 - Multi-line comments in R

On Wed, Aug 19, 2015 at 5:16 AM, Nathan Esau <nesau at sfu.ca>
wrote:
> I was wondering why the decision was made long ago to never implement
> multi-line comments in R. I feel there are several argument to be made for
> why the R language should have multi-line comments.
>
> 1. Many programming languages (including some which are commonly used for
> statistics, such as python, matlab and SAS) have this feature.
 Python doesn't have a multi-line comment.

 You can use triple-quoted strings in Python to quote a large chunk of
text, which won't generate any bytecode and so has no executable
effect:

def foo(x)
 y = x * 2
 """
 well what now
 lets have a comment
 """
 return(y)

A similar thing is possible in R:

 foo = function(x){
    "this is a test.
where
you can comment"
    return(x*2)
}

However I don't know if this causes any executable effect - its
possible R evaluates the string in some way.... Anyone want to test.

Yes, you have to escape any string quote marks in your comment, but in
python you have to escape any triple-quote marks.

Barry

On Thu, Aug 20, 2015 at 8:23 AM, Barry Rowlingson <
b.rowlingson at lancaster.ac.uk> wrote:
> On Wed, Aug 19, 2015 at 5:16 AM, Nathan Esau <nesau at sfu.ca> wrote:
> > I was wondering why the decision was made long ago to never implement
> > multi-line comments in R. I feel there are several argument to be made
> for
> > why the R language should have multi-line comments.
> >
> > 1. Many programming languages (including some which are commonly used
for
> > statistics, such as python, matlab and SAS) have this feature.
>
>  Python doesn't have a multi-line comment.
>
>  You can use triple-quoted strings in Python to quote a large chunk of
> text, which won't generate any bytecode and so has no executable
> effect:
>
> def foo(x)
>  y = x * 2
>  """
>  well what now
>  lets have a comment
>  """
>  return(y)
>
> A similar thing is possible in R:
>
>  foo = function(x){
>     "this is a test.
> where
> you can comment"
>     return(x*2)
> }
>
> However I don't know if this causes any executable effect - its
> possible R evaluates the string in some way.... Anyone want to test.
>
>
Well, my guess is that the string, when created, would be interned in the
global string cache. That's unlikely to have any real bearing on anything R
is doing, but it is technically an effect.

Also, in the script case/top-level-expression it would affect .Last.value,
I think, though not in the particular case you posted.

~G

> Yes, you have to escape any string quote marks in your comment, but in
> python you have to escape any triple-quote marks.
>
> Barry
>
> ______________________________________________
> R-devel at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-devel
>


-- 
Gabriel Becker, PhD
Computational Biologist
Bioinformatics and Computational Biology
Genentech, Inc.

	[[alternative HTML version deleted]]