[R] [FORGED] Re: Block comment?

Rolf Turner r.turner at auckland.ac.nz
Sun Sep 3 06:49:04 CEST 2017

On 03/09/17 12:29, Duncan Murdoch wrote:

> On 02/09/2017 6:57 PM, Rolf Turner wrote:
>> On 03/09/17 03:56, William Dunlap via R-help wrote:
>>> Is the reason you want a block comment containing code (as opposed to
>>> arbitrary text) that you want to be able to easily run the commented out
>>> code?  If so the 'if()' construct has the advantage that you only 
>>> need to
>>> change code at the start of the comment, not at both ends.
>>> The if(FALSE) could be if(isTRUE(getOption("DEBUG_ISSUE_XYZ"))) so you
>>> would not even have to change code to re-enable the debugging code, just
>>> call options(DEBUG_ISSUE_XYX=TRUE)).
>> (a) The foregoing is getting too subtle for my feeble brain.
>> (b) A fundamental problem with the
>>      if(FALSE) {
>>         ...
>>      }
>> paradigm is that the enclosed code must be syntactically valid, and
>> there are certainly situations in which one might wish to comment out
>> sections of code that are *not* syntactically valid.  E.g. one might
>> wish to comment out *part* of a piece of syntactically valid code for
>> the purpose of experimenting with an alternative approach.
> If the code is not syntactically valid, why would you expect the block 
> comment to be syntactically valid?

I thought I had made that clear.  One might wish to comment out a 
*piece* of syntactically valid code (with a view to replacing it).
The piece commented out might not be syntactically valid simply because 
it is *just a piece* and might thereby be incomplete.

> The proposal at the start of this 
> thread was that #{ would open the block and would be matched by }# to 
> close the block.  What if the closing sequence occurred within the block 
> unintentionally?  Then the poor feeble programmer would be even more 
> confused.

Do not the same considerations essentially apply to the well established
/* .... */ convention used in C?  Well maybe you simply *can't* get the 
"*/" string within a block of C code, but still ....

If "#{....}#" runs this risk, then some other construction which doesn't 
run the risk could be used.

> I like the current rule: 

De gustibus non disputandum.

> any line starting with # is a comment. 
> (Actually the rule is a bit more subtle than that, but it's close.)
> If I want to comment out a block, I can spend a long time typing # at 
> the start of every line, or I can ask my editor to do it.  I don't need 
> to worry if something in the block unintentionally closes it, because 
> that's impossible.  If the first line is a comment, all the rest are too.

I don't follow the foregoing, but no matter.  I'm slow.

This issue is quite obviously No Big Deal.  Block comments are a 
convenience that it would be nice to have, but obviously one can live 
without them and not suffer unduly.



Technical Editor ANZJS
Department of Statistics
University of Auckland
Phone: +64-9-373-7599 ext. 88276

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