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From: ccc31807 on 24 Feb 2010 18:08
Learning Lisp is like pulling teeth, except more painful!

Here is a code snippet copied directly from Figure 11.2, page 178, of
Graham's 'ANSI Common Lisp':

(defclass rec ()
(height width))
(defclass cir ()
(radius))
(defmethod area ((x rec))
(* (slot-value x 'height) (slot-value x 'width )))
(defmethod area ((x cir))
(* pi (expt (slot-value x 'radius) 2)))

Here is the error message gives when I try to compile this:

NO-APPLICABLE-METHOD: When calling #<GENERIC-FUNCTION FIND-METHOD>
with arguments (#<COMPILED-CLOSURE
AREA>
NIL (REC) NIL), no method is applicable.
[Condition of type METHOD-CALL-TYPE-ERROR]

I've tried the usual sources of help, including Keene, Lamkins, and
Seibel, and the HyperSpec, but I still can't figure out why this won't
compile.

Like I said, more painful than pulling teeth ... unless somebody notes
that I made a stupid typo that I have overlooked.

CC.
From: Zach Beane on 24 Feb 2010 18:28

> Here is a code snippet copied directly from Figure 11.2, page 178, of
> Graham's 'ANSI Common Lisp':
>
> (defclass rec ()
> (height width))
> (defclass cir ()
> (radius))
> (defmethod area ((x rec))
> (* (slot-value x 'height) (slot-value x 'width )))
> (defmethod area ((x cir))
> (* pi (expt (slot-value x 'radius) 2)))
>
> Here is the error message gives when I try to compile this:

I copied your snippet into a file called "scratch.lisp" and did
(compile-file "scratch.lisp") and didn't get any errors. What kind of
compiling did you do that triggered an error?

Zach
From: refun on 24 Feb 2010 18:41
In article <5bf2d29e-ea74-4c9c-a67d-e10c46b8e14f(a)d27g2000yqf.googlegroups.com>,
cartercc(a)gmail.com says...
>
> Learning Lisp is like pulling teeth, except more painful!
>
> Here is a code snippet copied directly from Figure 11.2, page 178, of
> Graham's 'ANSI Common Lisp':
>
> (defclass rec ()
> (height width))
> (defclass cir ()
> (radius))
> (defmethod area ((x rec))
> (* (slot-value x 'height) (slot-value x 'width )))
> (defmethod area ((x cir))
> (* pi (expt (slot-value x 'radius) 2)))
>
> Here is the error message gives when I try to compile this:
>
> NO-APPLICABLE-METHOD: When calling #<GENERIC-FUNCTION FIND-METHOD>
> with arguments (#<COMPILED-CLOSURE
> AREA>
> NIL (REC) NIL), no method is applicable.
> [Condition of type METHOD-CALL-TYPE-ERROR]
>
> I've tried the usual sources of help, including Keene, Lamkins, and
> Seibel, and the HyperSpec, but I still can't figure out why this won't
> compile.
>
> Like I said, more painful than pulling teeth ... unless somebody notes
> that I made a stupid typo that I have overlooked.
>
> CC.


Your code works fine here (on SBCL). I don't see anything weird with it, except
that you didn't define any accessors or initargs.
Here's some test code:
(let ((rec (make-instance 'rec))
(cir (make-instance 'cir)))
(with-slots (height width) rec
(setf height 10 width 20)
(setf (slot-value cir 'radius) 30)
(values
(area rec)
(area cir)))) ;=>200, 2827.4333882308138d0

Or rewritten with initargs/accessors.

(defclass rectangle ()
((height :initarg :height :accessor height)
(width :initarg :width :accessor width)))

(defclass circle ()
((radius :initarg :radius :accessor radius)))

(defmethod area ((x rectangle))
(* (height x) (width x)))

(defmethod area ((x circle))
(* pi (expt (radius x) 2)))

(let ((rec (make-instance 'rectangle :height 10 :width 20))
(cir (make-instance 'circle :radius 30)))
(values (area rec) (area cir))) ;=>200, 2827.4333882308138d0

From: Tim Bradshaw on 24 Feb 2010 19:26
On 2010-02-24 23:08:02 +0000, ccc31807 said:

> (defclass rec ()
> (height width))
> (defclass cir ()
> (radius))
> (defmethod area ((x rec))
> (* (slot-value x 'height) (slot-value x 'width )))
> (defmethod area ((x cir))
> (* pi (expt (slot-value x 'radius) 2)))
>
> Here is the error message gives when I try to compile this:

What do you mean by "when I try to compile this"? If you put the above
in a file and compile it with COMPILE-FILE I think this should
definitely be fine.

From: Patrick May on 24 Feb 2010 20:12
ccc31807 <cartercc(a)gmail.com> writes:
> (defclass rec ()
> (height width))
> (defclass cir ()
> (radius))
> (defmethod area ((x rec))
> (* (slot-value x 'height) (slot-value x 'width )))
> (defmethod area ((x cir))
> (* pi (expt (slot-value x 'radius) 2)))
>
> Here is the error message gives when I try to compile this:
>
> NO-APPLICABLE-METHOD: When calling #<GENERIC-FUNCTION FIND-METHOD>
> with arguments (#<COMPILED-CLOSURE
> AREA>
> NIL (REC) NIL), no method is applicable.
> [Condition of type METHOD-CALL-TYPE-ERROR]

I cut and pasted that into SBCL on OSX and it was fine. What Lisp
are you using?

Regards,

Patrick

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