On 4/27/05, Ali - <saveez@hotmail.com> wrote: 
> 
> 
> 
> > >
> > > Assume we have a function like:
> > >
> > > foo <- function(x, y)
> > >
> > > how is it possible to define a binary indexing operator, denoted by $,
> >so
> > > that
> > >
> > > x$y
> > >
> > > functions the same as
> > >
> > > foo(x, y)
> >
> > Here is an example. Note that $ does not evaluate y so you have
> >to do it yourself:
> >
> >x <- structure(3, class = "myclass")
> >y <- 5
> >foo <- function(x,y) x+y
> >"$.myclass" <- function(x, i) { i <- eval.parent(parse(text=i)); foo(x, 
> i)
> >}
> >x$y # structure(8, class = "myclass")
> 
> what about this approach:
> 
> foo <- function(x, y) x+y
> assign("$", foo)
> 
> would this overwrite $ 

 Yes.
 and make R to forget its definitions in the global
environment?
 Yes.
 Your construct might still be used in a local environment.
 f <- function(x,y) {
 "$" <- function(x,y) x+y
 x$y
}
f(1,2) # 3
 # or
z <- local({ 
 "$" <- function(x,y) x+y
 x <- y <- 3
 x$y
})
z # 6
 works and outside of f and the local, $ works normally.

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