Explanation of macros; Haskell macros

[Coby Beck]

"Pascal Costanza" <costanza at web.de> wrote in message
news:bnscfb$p1k$1 at newsreader2.netcologne.de...
>
> The essence of this is as follows:
>
> (defmacro my-cond (&body body)
>    `(cond ,@(append body '(t (handle-the-default-case))))
>

Just to provide a more apparently general (and working ;) version, analogous
to CL's ECASE:

CL-USER 90 >
(defmacro econd (&body body)
  `(cond ,@(append body
                   `((t (error (format nil
                                       "fell through ECOND form.  could not
satisfy any of the following: ~{~%~A~}~%"
                                       (mapcar #'(lambda (cond)
                                                   (car cond))
                                               ',body))))))))
ECOND

CL-USER 91 > (econd
                ((= 3 4) "foo")
                ((= 4 4) "bar"))
"bar"

CL-USER 92 > (econd
                ((= 3 4) "foo")
                ((= 4 5) "bar"))

Error: fell through ECOND form.  could not satisfy any of the following:
(= 3 4)
(= 4 5)

  1 (abort) Return to level 0.
  2 Return to top loop level 0.

Type :b for backtrace, :c <option number> to proceed,  or :? for other
options


-- 
Coby Beck
(remove #\Space "coby 101 @ big pond . com")