[Rd] [WISH / PATCH] possibility to split string literals across multiple lines

[Duncan Murdoch]

On 14/06/2017 6:45 AM, Andreas Kersting wrote:
> On Wed, 14 Jun 2017 06:12:09 -0500, Duncan Murdoch <murdoch.duncan at gmail.com> wrote:
>
>> On 14/06/2017 5:58 AM, Andreas Kersting wrote:
>>> Hi,
>>>
>>> I would really like to have a way to split long string literals across
>>> multiple lines in R.
>>
>> I don't understand why you require the string to be a literal.  Why not
>> construct the long string in an expression like
>>
>>   paste0("aaa",
>>          "bbb")
>>
>> ?  Surely the execution time of the paste0 call is negligible.
>>
>> Duncan Murdoch
>
> Actually "execution time" is precisely one of the reasons why I would like to see this feature as - depending on the context (e.g. in a tight loop) - the execution time of paste0 (or probably also glue, thanks Gabor) is not necessarily insignificant.

You also need to consider implementation time.  This is not just changes 
to R itself; trailing backslashes *are* used in some packages (e.g. 
geoparser), so those packages would need to be identified and modified 
and resubmitted to CRAN.

Core changes to existing behaviour need really strong arguments, and I'm 
just not seeing those here.

Duncan Murdoch

> The other reason is style: I think it is cleaner if we can construct such a long string literal without the need for a function call.
>
> Andreas
>
>>>
>>> Currently, if a string literal spans multiple lines, there is no way to
>>> inhibit the introduction of newline characters:
>>>
>>>  > "aaa
>>> + bbb"
>>> [1] "aaa\nbbb"
>>>
>>>
>>> If a line ends with a backslash, it is just ignored:
>>>
>>>  > "aaa\
>>> + bbb"
>>> [1] "aaa\nbbb"
>>>
>>>
>>> We could use this fact to implement string splitting in a fairly
>>> backward-compatible way, since currently such trailing backslashes
>>> should hardly be used as they do not have any effect. The attached patch
>>> makes the parser ignore a newline character directly following a backslash:
>>>
>>>  > "aaa\
>>> + bbb"
>>> [1] "aaabbb"
>>>
>>>
>>> I personally would also prefer if leading blanks (spaces and tabs) in
>>> the second line are ignored to allow for proper indentation:
>>>
>>>  >   "aaa \
>>> +    bbb"
>>> [1] "aaa bbb"
>>>
>>>  >   "aaa\
>>> +    \ bbb"
>>> [1] "aaa bbb"
>>>
>>> This is also implemented by this patch.
>>>
>>>
>>> An alternative approach could be to have something like
>>>
>>> ("aaa "
>>> "bbb")
>>>
>>> or
>>>
>>> ("aaa ",
>>> "bbb")
>>>
>>> be interpreted as "aaa bbb".
>>>
>>> I don't know the ins and outs of the parser of R (hence: please very
>>> carefully review the attached patch), but I guess this would be more
>>> work to implement!?
>>>
>>>
>>> What do you think? Is there anybody else who is missing this feature in
>>> the first place?
>>>
>>> Regards,
>>> Andreas
>>>
>>>
>>>
>>> ______________________________________________
>>> R-devel at r-project.org mailing list
>>> https://stat.ethz.ch/mailman/listinfo/r-devel
>>>
>
>