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Re: Differences between Elisp and Lisp
From: |
Friedrich Dominicus |
Subject: |
Re: Differences between Elisp and Lisp |
Date: |
01 May 2003 07:41:54 +0200 |
User-agent: |
Gnus/5.0808 (Gnus v5.8.8) XEmacs/21.4 (Native Windows TTY Support) |
Lars Magne Ingebrigtsen <lmi@gnus.org> writes:
> "Stefan Monnier" <monnier+gnu.emacs.help/news/@flint.cs.yale.edu> writes:
>
> >>>>>> "Lars" == Lars Magne Ingebrigtsen <lmi@gnus.org> writes:
> >> and dispatching functions based on type would be nice.
> >
> > Never heard that one. What exactly would you like to see ?
>
> The Common Lisp `defmethod' thingie. Which is a part of CLOS, I
> guess, but wouldn't have to be. But one would need a type system.
>
> (defmethod do-stuff ((arg string))
> ... do stuff with a string)
>
> (defmethod do-stuff ((arg number))
> ... do stuff with a number)
What you have missed you can have dispatch on multiple parameters
(that does not work with eieio)
(defmethod (do-stuff ((arg-1 string) (arg-2 string) ....
>
> And then one could just say (do-stuff whatever) here and there.
>
> This is really just syntactical sugar on the "pattern"
Not fully.
>
> Perhaps eieio already provides this?
Partly, it just allows the first parameter to be constrained.
Here and example
;;; eieio-example.el --- Example for defmethod in eieio
(require 'eieio)
(defclass some-num ()
((val :accessor val :initarg :val)))
(defclass some-string ()
((val :accessor val :initarg :val)))
(defmethod g+ ((val some-num) val-2)
(+ (val val) val-2))
(defmethod g+ ((val some-string) val-2)
(concatenate 'string (val val) val-2))
usage:
(g+ (make-instance 'some-num :val 10) 10) -> 20
(g+ (make-instance 'some-string :val "foo") "bar" -> "foobar"
Not that this is a good example, but it shows how that stuff works
Regards
Friedrich