Class-attribute and method dispatch for the function-class

Hi everyone.

I played with operator overloading for functions and came upon a few
peculiarities. I basically wanted to do something like this:

Ops.function<-function(e1, e2) {
  Op <- getMethod(.Generic)
   if(missing(e2)) return(function(...) Op(e1(...)) )
   if(is.function(e2)) return(function(...) Op(e1(...),e2(...)) )
   function(...) Op(e1(...),e2)
}

I expected to be able to do for example:

f <- function(x) cos(x^2 - 1)
g <- f^2 - f

Of course g will not be very efficient, because it will call f twice
for each evaluation. But the approach is very general and would often
help to avoid anonymous functions.

Now here is the problem: When I do the above, I get
?Error in f^2: non-numeric argument to binary operator?

It appears that R does not do dispatch. I guess this is because f is
not an object

is.object(f)

[1] FALSE

When I explicitly set the class of f to ?function? (i.e. the same as
before) it seems like f becomes an object and everything works:

class(f)<-class(f)
g <- f^2 - f
g

function(...) Op(e1(...),e2(...))
<environment: 0x026f29dc>

Is there any way of getting dispatch to work without explicitly making
functions an object?

In addition I noticed some strange behavior with what I guess is the
treatment of primitives. This might be a question better suited for
r-devel, but since it ties in with the above I?ll still include it
here: Starting with a function and a copy of it

u <- function(x) x+1
v <- u

we have

is.object(u)

[1] FALSE

is.object(v)

[1] FALSE
Now we explicitly set the class of u and it becomes an object, while
the copy remains unchanged.

class(u)<-class(u)
is.object(u)

[1] TRUE

is.object(v)

[1] FALSE

Now instead of u lets use a primitive function like sum and a copy mysum:

mysum <- sum
is.object(sum)

[1] FALSE

is.object(mysum)

[1] FALSE
If we change the class of mysum, the original function sum becomes an
object, too!

class(mysum)<-class(mysum)
is.object(mysum)

[1] TRUE

is.object(sum)

[1] TRUE

Is this intended?

Best regards,
Jonas Rauch