[R] fun with S4 method recursion

[Ross Boylan]

Apparently using an existing function as the definition for a method is
a no-no (at least as I'm doing it), producing infinite recursion.
setClass("A",
         representation(model="ANY")
         )
fiddle <- function(self) {
  1
}

setMethod("fiddle",
          signature(self="A"),
          definition = fiddle  ### problem
          )

setClass("B",
         representation(err="ANY"),
         contains="A"
         )

setMethod("fiddle",
          signature(self="B"),
          definition = function(self){
            callNextMethod()
            2
          })

b <- new("B", model=4, err=5)
fiddle(b)

produces
Error: protect(): protection stack overflow

On the other hand, if the line marked ### problem becomes
	definition = function(self) 1
everything works OK.

I think the definition of the generic is ending up as the method for A.
This surprised me, because I thought this was the standard way to
approach setting up a method ("Any ordinary function can be converted
into a generic by simply setting a method for it; ... the initial,
unique method (the body of the function) becomes the default method" pp.
322-323; "a generic function is created automatically by specifying a
method for any existing function.  This is by far the more common
situation" p 348--all pages in the green book).  It also surprised me
because of the note that setMethod makes a local copy of the function
given as the definition argument (bottom of p. 323).

Does the behavior of R differ from that described in the green book when
the name of a function appears in the definition argument of setMethod?
If not, what have I misunderstood?

Aside: my first real attempt didn't have 
	fiddle <- function(self) {1}
using just 
	setMethod("fiddle", "A", function(self) 1)
That produces no existing definition for function 'fiddle'


Given all this, would this be a better model?
fiddle <- function(... # definition for A
# do NOT setMethod for class A signature
setMethod("fiddle", "B", function(self) #operations for B
So when I do the setMethod my original fiddle becomes the default
generic.

Thanks.
Ross