[Rd] Re: backtick notation

[Gabor Grothendieck]

> > assign and as.name are fairly limited.  For example, if you have a list or
> > data frame whose name is syntactically invalid it is quite difficult to
> > access or modify its columns.
>
> Yes. `weight in kg`[101]<-55 is pretty difficult to do with get() and
> assign() and lm(`weight in kg`~I(`height in m`^2)) is tricky too. The
> use is sort of similar to the single quotes in shell programming (but
> not quite). The choice of the backtick as quoting delimiter was mostly
> because that was the only one available....

Good point about the difficulty of using assign and get.

This leads to additional questions:

- is it desirable to make it easy to work with non-synactic names?

- if the previous point is yes, then is this use sufficiently 
  important to warrant a new syntactic element, viz. backquote?  
  For example, extending perhaps as.name could be extended so that
  it can be used on the left hand side of an assignment like this:
  as.name("height in m2")^2 or as.name("weight in kg")[101]<-55

- how far can this feature be pushed?   For example, backtick quoted
  names might be usable in string literals as in perl:
  print("variable x is `x` and variable y is `y`")  or
  download.file("http://www.xyz.com?a=`a`&b=`b`")

I am not sure what the answers to these questions should be 
but in order to combat excessive growth of the syntax a new 
syntax addition usually is made to climb a higher barrier than 
a feature which does not.