Are lambda functions CLOS objects?

Question

When I do this:

(defparameter thing #'(lambda () (+ 1 1)))

The returned value for thing is

#<FUNCTION (LAMBDA ()) {53A11BEB}>

This print out looks a lot like the print-object for a CLOS.

So, I thought id like to see the actual function detail in the print-object.

I cannot seem to find out the name of the function object to use in my list-class-slots function:

(defun list-class-slots (class)
  (mapcar #'sb-mop::slot-definition-name
     (sb-mop::class-direct-slots (class-of (make-instance class)))))

I tried sb-mop::funcallable-standard-class but this returns nil. I also tried function and the error told me to use the funcallable-standard-class.

Am I wrong here? is the original lambda printout NOT related to CLOS at all? if not, what is the source of the function printout?

Answer 1

A function created with lambda is an object, yes. It's an instance of the system class function:

* (class-of thing)
#<SB-PCL:SYSTEM-CLASS COMMON-LISP:FUNCTION>

Functions are printed in an implementation-dependent manner, in practice often in the convention for an unreadable value (#<...>). It appears that SBCL has a specialization of the print-object generic method for functions.

* (find-method #'print-object '() (mapcar #'find-class '(function t)))
#<STANDARD-METHOD COMMON-LISP:PRINT-OBJECT #'T {100042B4C3}>

Indeed, here it is. You can poke around in it to see how it works.

Answer 2

In such a printed representation #<FUNCTION (LAMBDA ()) {53A11BEB}>, the first thing usually (by convention) is the type of the thing. Thus it is of type FUNCTION. See the standard.

CLOS also has a feature to define function objects which are both CLOS objects and callable functions. The use of those is rarely seen.

cannot seem to find out the name of the function object

The function object does not have a name.