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

[Mark van der Loo]

Having some line-breaking character for string literals would have benefits
as string literals can then be constructed parse-time rather than run-time.
I have run into this myself a few times as well. One way to at least
emulate something like that is the following.

`%+%` <- function(x,y) paste0(x,y)

"hello" %+%
  " pretty" %+%
  " world"


-Mark



Op wo 14 jun. 2017 om 13:53 schreef Andreas Kersting <r-devel at akersting.de>:

> 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.
>
> 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
> > >
>
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