Explanation of macros; Haskell macros

[Olaf Klischat]

"Coby Beck" <cbeck at mercury.bc.ca> writes:

> "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))))))))


Just for the record: Is the "append" stuff necessary? Why not write
this as

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

?

Olaf
-- 
Olaf Klischat            | Fraunhofer ISST
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