[Rd] syntax confusion with function/non-function objects (PR#694)

[J.C.Rougier@durham.ac.uk]

On Fri, 13 Oct 2000, Luke Tierney wrote:

> > In general you can have any expression evaluating to the function
> > to be called. If you do f(x)(3), f(x) may or may not be a function
> > and you can only detect whether it is one at runtime.

> I agree--I'd call this a type error in evaluation, not a syntax error.
> 
> One thing to keep in mind is that R expressions can be used for things
> other that evaluation, for example in representing aspects of models.
> Someone might want at some point to attach meaning to something like
> 
> 	y ~ 2(x)+z
> 
> That would be impossible (or at least very dificult) if the expression
> were made syntactically invalid.
> 
> It would be possible to have a semantic checking tool for R that walks
> over the code and warns when it sees such an expression, but it should
> not be considered an error since it could be legitimate.

I see the point.  It might be helpful to change the R error message in
line with Splus so that the source of the error is easy to identify.

Jonathan.

Jonathan Rougier                       Science Laboratories
Department of Mathematical Sciences    South Road
University of Durham                   Durham DH1 3LE
http://www.maths.dur.ac.uk/stats/people/jcr/jcr.html


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