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bug#6583: 23.2; cl loop macro with `and' clause


From: Thierry Volpiatto
Subject: bug#6583: 23.2; cl loop macro with `and' clause
Date: Thu, 08 Jul 2010 09:40:22 +0200
User-agent: Gnus/5.110011 (No Gnus v0.11) Emacs/24.0.50 (gnu/linux)

Kevin Ryde <address@hidden> writes:

> Evaluating
>
>     (require 'cl)
>     (loop for elem in '(1 2 3)
>           for k = elem and j = 99
>           do
>           (print k))

IMHO this is not correct, 'and' clauses should be used after conditionals
(e.g if, when etc..)

,----
| ELISP>  (loop for elem in '(1 2 3)
|            for k = elem
|            if (oddp k)
|              collect k and do (print k))
`----

> shows
>
>     1
>     1
>     2

Instead of returning this, emacs should throw an error as SBCL does for
same code.

,----
| CL-USER> (loop for i in '(1 2 3)
|               for k = i and j = 99
|               (print k))
| ; Evaluation aborted.
`----

> where I thought it might be
>
>     1
>     2
>     3
>
> I'm don't know much about the cl loop macro but thought the `for k' step
> would be evaluated after the `for elem' step, "sequential" per the cl
> info manual near the end of "For Clauses"
>
>     If you include several `for' clauses in a row, they are treated
>     sequentially
>
> The 1,2,3 is what you get from pasting the same form into clisp, if that
> suggests what an actual common lisp does or should do.  And in Emacs
> it's had if you omit the "and j",
>
>     (loop for elem in '(1 2 3)
>           for k = elem
>           do
>           (print k))
>     =>
>     1 2 3
>
> Nosing around the macro expansion I wondered if the "step" of k/j gets
> mispositioned if there's an `and', but it's hard to be sure.
>
>
> I struck this when making a loop over an alist where I thought to take
> apart the key and value with an `and' as they didn't need to be
> sequential,
>
>     (loop for elem in my-alist
>           for k = (car elem) and v = (cdr elem)
>           do
>           ...
>
> Alas the effect of the "1 1 2" was to double the first element and omit
> the last.
>
>
> In GNU Emacs 23.2.1 (i486-pc-linux-gnu, GTK+ Version 2.20.0)
>  of 2010-05-16 on raven, modified by Debian
> configured using `configure  '--build' 'i486-linux-gnu' '--build' 
> 'i486-linux-gnu' '--prefix=/usr' '--sharedstatedir=/var/lib' 
> '--libexecdir=/usr/lib' '--localstatedir=/var/lib' 
> '--infodir=/usr/share/info' '--mandir=/usr/share/man' '--with-pop=yes' 
> '--enable-locallisppath=/etc/emacs23:/etc/emacs:/usr/local/share/emacs/23.2/site-lisp:/usr/local/share/emacs/site-lisp:/usr/share/emacs/23.2/site-lisp:/usr/share/emacs/site-lisp:/usr/share/emacs/23.2/leim'
>  '--with-x=yes' '--with-x-toolkit=gtk' '--with-toolkit-scroll-bars' 
> 'build_alias=i486-linux-gnu' 'CFLAGS=-DDEBIAN -g -O2' 'LDFLAGS=-g' 
> 'CPPFLAGS=''
>
> Important settings:
>   value of $LC_ALL: nil
>   value of $LC_COLLATE: nil
>   value of $LC_CTYPE: nil
>   value of $LC_MESSAGES: nil
>   value of $LC_MONETARY: nil
>   value of $LC_NUMERIC: nil
>   value of $LC_TIME: nil
>   value of $LANG: en_AU
>   value of $XMODIFIERS: nil
>   locale-coding-system: iso-latin-1-unix
>   default enable-multibyte-characters: t
>
>
>
>

-- 
Thierry Volpiatto
Gpg key: http://pgp.mit.edu/






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