Re: `list-of' macro snippet [regarding Comprehensions]

From	"Pascal J. Bourguignon" <pjb@informatimago.com>
Newsgroups	gnu.emacs.sources, gnu.emacs.help, comp.emacs, comp.lang.lisp, comp.lang.functional
Subject	Re: `list-of' macro snippet [regarding Comprehensions]
Date	2012-11-07 23:30 +0100
Organization	Informatimago
Message-ID	<87r4o56o6j.fsf@informatimago.com> (permalink)
References	(2 earlier) <f9dfcdb2-9d1c-4307-8d1b-588760466ed3@b12g2000vbg.googlegroups.com> <d909bf45-a8b5-4974-8135-a101af3531d6@y6g2000vbb.googlegroups.com> <87pq3vmlg5.fsf@informatimago.com> <556673a6-b350-49cc-905d-0662222ca071@g8g2000yqp.googlegroups.com> <3445356f-5bb8-4dcd-bd45-d98a4e103a2a@g18g2000vbf.googlegroups.com>

Cross-posted to 5 groups.

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Rivka Miller <rivkaumiller@gmail.com> writes:

> I still need someone to help me get the common-lisp comprehension code
> working on emacs.

Require cl and use defmacro* instead of defmacro:


(require 'cl)
(defmacro* comp ((e &rest qs) l2)
  (if (null qs) `(cons ,e ,l2)    ; rule A
      (let ((q1 (car qs))
            (q (cdr qs)))
        (if (not(eq (cadr q1) '<-)) ; a generator?
            `(if ,q1 (comp (,e ,@q),l2) ,l2) ; rule B
            (let ((v (car q1))      ; rule C
                  (l1 (third q1))
                  (h (gentemp "H-"))
                  (us (gentemp "US-"))
                  (us1 (gentemp "US1-")))
              `(labels ((,h (,us)     ; corresponds to a letrec
                          (if (null ,us) ,l2
                              (let ((,v (car ,us))
                                    (,us1 (cdr ,us)))
                                (comp (,e ,@q) (,h ,us1))))))
                 (,h ,l1)))))))

(macroexpand '(comp (e (< 1 2)) l2))
--> (if (< 1 2) (comp (e) l2) l2)
(macroexpand '(comp (e) l2))
--> (cons e l2)

-- 
__Pascal Bourguignon__
http://www.informatimago.com

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Re: `list-of' macro snippet [regarding Comprehensions] Rivka Miller <rivkaumiller@gmail.com> - 2012-10-28 17:49 -0700
  Re: `list-of' macro snippet [regarding Comprehensions] Rivka Miller <rivkaumiller@gmail.com> - 2012-10-28 19:20 -0700
    Re: `list-of' macro snippet [regarding Comprehensions] Rivka Miller <rivkaumiller@gmail.com> - 2012-11-02 19:06 -0700
      Re: `list-of' macro snippet [regarding Comprehensions] "Pascal J. Bourguignon" <pjb@informatimago.com> - 2012-11-03 04:09 +0100
        Re: `list-of' macro snippet [regarding Comprehensions] Rivka Miller <rivkaumiller@gmail.com> - 2012-11-03 14:57 -0700
          Re: `list-of' macro snippet [regarding Comprehensions] Rivka Miller <rivkaumiller@gmail.com> - 2012-11-07 09:08 -0800
            Re: `list-of' macro snippet [regarding Comprehensions] "Pascal J. Bourguignon" <pjb@informatimago.com> - 2012-11-07 23:30 +0100

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