[R] Backquote in R syntax

[Prof Brian Ripley]

?Quote tells you all about quotes in R (and so does ?backquote in 
R-devel, but many people call it backtick and that is all 2.3.1 has).

On Mon, 7 Aug 2006, Ted.Harding at nessie.mcc.ac.uk wrote:

> Hi Folks,
> Can someone satisfy my curiosity (well, at least about
> the following query!)
> 
> Reading the draft proofs of an article I've been asked
> to look through, I find the typesetter has set what
> would normally be entered as
> 
>   source("xyz.R")   or   source('xyz.R')
> 
> as
> 
>   source(`xyz.R')
> 
> i.e. it has come out with an opening backquote, then
> xyz.R, then a closing forward quote. I suspect the
> intervention of "intelligent" software (à la Word's
> "clever quotes").
> 
> Well, the cure is clear and I'm not asking about that.
> But I got curious about what role the backquote might
> play in R syntax (if any). As a start I tried typing
> that in as it stands:
> 
>    source(`xyz.R')
> ## and then you get the "continuation +" as if it were
> ##   incomplete, so I tried a closing parenthesis:
> + )
> Error: unprotect_ptr: pointer not found
> 
> So it wasn't a mere syntax error (which would have caused
> an error message saying just that) -- using the backquote
> caused R to try to do something.
> 
> So now I'm wondering what the effect of "`" is, in R.
> 
> Statutory Declaration: I have performed an R Site Search
> for "backquote" obtaining 9 hits none of which seems to
> address this question.
> 
> Best wishes to all,
> Ted.
> 
> --------------------------------------------------------------------
> E-Mail: (Ted Harding) <Ted.Harding at nessie.mcc.ac.uk>
> Fax-to-email: +44 (0)870 094 0861
> Date: 07-Aug-06                                       Time: 10:25:31
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-- 
Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272866 (PA)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595