Discrepancy between is.list() and is(x, "list")

I know I said that I had no further comments on object oriented semantics.
However, I found a contradiction in the R documentation.

So, there are implicit classes, but *only when the data object is NOT an

"R object"

In the R Language Definition:

The R specific function typeof returns the type of an R object.
Lists have elements, each of which can contain any type of R object
Symbols refer to R objects.
Unlike most other R objects, environments are not copied

So, according the the R Language Defintion, all objects in R, are R objects.

However, in the help page for UseMethod(), which you've already mentioned:

An R object is a data object which has a class attribute (and this can be

tested by is.object).

So, according to this, an object in R, isn't necessarily an R object.

These are contradictory to each other.
And I believe that the R Language Definition is correct.
So, the help page for UseMethod() should be changed to match the language
definition.

Understanding the distinction between base types and S3 classes
is very important to make this sort of question precise

Note that the R Language Definition does not mention either "base types" or
"S3 classes".
So, should I be understanding *your* distinction between them?

I do agree with Gabe that (in some cases), using
formal (aka "S4") classes is really what one should do

S4 doesn't always do intuitive things, either.

Try the following example:

library (Matrix)
m = Matrix (1:24, 4, 6)

#expected output
print (m)

#not expected output
print (m, quote=FALSE)

However, I still may consider using S4, especially where I would otherwise
use a named list.